Analysis of Heat Waves and Urban Heat Island Effects in Central European Cities and Implications for Urban Planning The International Bank for Reconstruction and Development/ The World Bank 1818 H Street, N.W. Washington, D.C. 20433, U.S.A April 2020 Disclaimer This document is the product of work performed by World Bank staff and consultants. The findings, interpretations, and conclusions expressed in this document do not necessarily reflect the views of the Executive Directors of the World Bank or the governments they represent. The World Bank does not guarantee the accuracy of the data included in this work. The boundaries, colors, denomination, and other information shown in any map in this work do not imply any judgment on the part of The World Bank concerning the legal status of any territory or the endorsement or acceptance of such boundaries. Rights and Permissions The material in this work is subject to copyright. The World Bank encourages dissemination of its knowledge, this work may be reproduced, in whole or in part, for noncommercial purposes as long as full attribution to this work is given. Any queries on rights and licenses, including subsidiary rights, should be addressed to the Office of the Publisher, The World Bank, 1818 H Street NW, Washington, DC 20433, USA; fax: 202-522-2422; e-mail: pubrights@worldbank.org. Suggested citation: World Bank. 2020. Analysis of Heat Waves and Urban Heat Island Effects in Central European Cities and Implications for Urban Planning. Washington, D.C.: World Bank. Acknowledgements This report was prepared as part of regional technical assistance titled “Strategies and Options for Scaling Up Disaster Risk Management in ECA Countries,” supported by a grant from the Global Facility for Disaster Reduction and Recovery. The World Bank team was led by Zuzana Stanton-Geddes, Alanna Simpson, Anita Ellmauer-Klambauer, and Solene Dengler. The analysis was prepared by a team of experts from the Zentralanstalt für Meteorologie und Geodynamik (ZAMG), led by Michael Staudinger, Maja Zuvela-Aloise, Rosmarie de Wit, and Brigitta Hollósi, with contributions from Astrid Kainz, Sandro Oswald, Claudia Hahn, Robert Goler, and international experts Anita Bokwa from the Jagiellonian University in Kraków, Ivana Herceg Bulic from the University of Zagreb, and Melita Percec Tadic and Irena Nimac from the Croatian Meteorological and Hydrological Service. The team would like to thank David Sislen for overall guidance, and the peer reviewers Xueman Wang, Carli Bunding-Venter, Yann Kerblat, and Debashree Poddar. The report was edited by Anne Himmelfarb and designed by Brigitta Hollósi. About this report This report provides an overview of the urban heat island (UHI) effect in Central European cities and its implications for sustainable development. Directed at policy makers, practitioners, and the wider public, the report explains the UHI effect and its drivers, as well as potential risk management and adaptation measures to address them. One of the report’s key messages is that in the context of cities and changing climate, policy and investment decisions can be facilitated by scientific approaches that provide information on current and future climate, and that increase understanding of measures to reduce UHI effects. Along with potential adaptation measures, this report also highlights the need to increase public awareness of, and emergency preparedness for, urban heat impacts on people and societies. The report also includes a number of city examples and case studies, selected based on availability of information, and relevance for other cities in the region. In introducing adaptive and preparedness policy options, this report also promotes the integration of disaster risk management approaches in the urban context. This integration is illustrated through a roadmap for increased resilience to urban heat. This roadmap highlights the key steps that cities can take to better understand the scope of UHI effects and in turn integrate this information into broader resilience or urban development plans and strategies. In the process of planning and implementing specific adaptation measures for urban heat, cities would have to consider a range of aspects, including technical, institutional, regulatory, social, environmental, financial, and many others, which go beyond the scope of this report. A glossary of key terms used, along with further references, is provided at the front and at the back of this report respectively. 1 GLOSSARY EARLY WARNING SYSTEM ADAPTATION The set of capacities needed to Actions taken to manage climate generate and disseminate timely IMPACTS risk to an acceptable level, and meaningful warning Effects on natural and human systems. In taking advantage of any positive information to enable individuals, this report, the term “impacts” is used to opportunities that may arise. communities, and organizations refer to the effects of physical events and Adaptation options are possible threatened by a hazard to prepare climate change on natural and human measures and actions that can and to act appropriately and in systems. be implemented to improve sufficient time to reduce the adaptation to climate change. possibility of harm or loss. IMPERVIOUS SURFACE Surface covered by water-resistant ALBEDO materials such as asphalt, concrete, or The fraction of solar radiation ENSEMBLE stone, resulting in reduced evaporation and reflected by a surface or object, A group of parallel model hence higher heat loads and increased often expressed as a percentage. simulations used for climate storm-water runoff. projections. Variation in the results across the ensemble members ANTHROPOGENIC gives an estimate of uncertainty. INVERSION Made by people or resulting Multi-model ensembles that An increase of air temperature with height. from human beings or activities. include simulations by several models also include the impact of model differences. AbCd efgH iJklMn MITIGATION LOCAL CIRCULATION SYSTEM CITIZEN WEATHER STATION A weather Wind flow patterns typical for a The lessening of the station set up by an amateur observer, for local area, usually on a spatial potential adverse impacts of example located in the owner’s garden. The physical hazards (including scale between 10 and 100km. owners can submit their observations to human-induced impacts) online platforms, making data available for through actions that reduce various applications. LONGWAVE RADIATION This radiation originates by thermal hazard, exposure, and emission from the Earth's surface vulnerability; in terms of CLIMATE and its atmosphere out to space. climate change, a human intervention to reduce the Climate is usually defined as the average weather, or more rigorously, as the sources or enhance the sinks statistical description in terms of the mean of greenhouse gases. and variability of relevant quantities over a HAZARD period of time ranging from months to The potential occurrence of a natural or human-induced thousands or millions of years. Variability physical event that may cause loss of life, injury, or other may be due to natural internal processes health impacts, as well as damage and loss to property, within the climate system (internal infrastructure, livelihoods, service provision, and variability), or to variations in natural or environmental resources. anthropogenic external forcing (external variability). HEAT STORAGE The residual term in the surface energy balance wherein a CLIMATE SCENARIO layer or volume has a gain of heat resulting in a temperature A plausible and often simplified increase depending on the heat capacity of the material. representation of the future climate, based on an internally consistent set of HEAT WAVE climatological relationships that has been A period of abnormally hot weather. Heat waves and warm constructed for explicit use in investigating spells have various and, in some cases, overlapping the potential consequences of definitions. A detailed description is provided in Chapter 6. anthropogenic climate change, often serving as input to impact models. 2 GLOSSARY UNCERTAINTY An expression of the degree to which a value or relationship is unknown. Uncertainty may originate from many sources, such as quantifiable errors in RESILIENCE THERMAL STABILITY the data, ambiguously defined concepts or terminology, or uncertain The ability of a system and its The most stable projections of human behavior. Uncertainty can therefore be represented by component parts to anticipate, conditions in the quantitative measures (e.g., a range of values calculated by various models) absorb, accommodate, or recover atmosphere occur during or by qualitative statements reflecting the judgment of a team of experts. from the effects of a hazardous a temperature inversion. event in a timely and efficient URBAN CANYON manner, including through Defined as the space above the streets and between the buildings. ensuring the preservation, THERMAL STRESS restoration, or improvement of its A condition when URBAN ENERGY BALANCE essential basic structures and temperature becomes too The exchange of surface energy fluxes, primarily heat, in urban areas. functions. extreme for the body to manage. URBAN HEAT ISLAND The relative warmth of a city compared with surrounding rural areas, RISK associated with changes in runoff, the heat retention, changes in surface The potential for consequences THERMOREGULATION albedo, and so on. The full definition is provided in Chapter 1. where something of value is at A process that allows the stake and where the outcome is living body to maintain its URBAN HEAT LOAD uncertain, recognizing the core internal temperature. Excessive heat conditions in urban areas. The term „heat load” is diversity of values. Risk is often sometimes used in literature as a synonym for „heat stress”, which is represented as probability of related to human thermal comfort. occurrence of hazardous events or TROPICAL NIGHTS trends multiplied by the impacts if Days where the URBAN MICROCLIMATE these events or trends occur. Risk minimum of air A local set of atmospheric conditions in a relatively small area (typically results from the interaction of temperature does not up to 100 m) that differ from those in the surrounding areas. vulnerability, exposure, and fall below 20.0°C. hazard. URBAN-RURAL GRADIENTS op Qr Stu VWxYz The difference in temperature between the urban and surrounding rural regions. PARAMETRIZATION In climate models, the technique of SCENARIO WASTE HEAT representing processes that cannot A plausible and often simplified It is the unused heat produced by be explicitly resolved at the spatial or description of how the future machines, objects (such as automobiles or temporal resolution of the model may develop based on a air conditioning) or processes (industry) (sub-grid-scale processes) by coherent and internally transferred to the surrounding relationships between model- consistent set of assumptions environment, contributing to the UHI resolved larger-scale flow and the about driving forces and key effect. area- or time-averaged effect of such relationships. sub-grid-scale processes. SKY VIEW FACTOR VULNERABILITY A geometric ratio that The propensity or predisposition to be adversely PREPAREDNESS affected. Vulnerability encompasses a variety of expresses the fraction of the Capacity of entities to anticipate, concepts, including sensitivity or susceptibility to radiation output from one cope and recover from the negative harm and lack of capacity to cope and adapt. surface that is intercepted by impacts from disasters and another. emergencies. SOIL SEALING PROJECTION A process for changing the A potential future evolution of a nature of the soil and covering quantity or set of quantities, often it by impervious materials, such computed with the aid of a model. as concrete, metal, and tarmac. Projections are distinguished from predictions in order to emphasize SUMMER DAYS that projections involve Days where the maximum of assumptions—for example, about air temperature is equal or future socioeconomic and higher than 25.0°C. technological developments that may or may not be realized—and are therefore subject to substantial uncertainty. 3 Table of Contents Chapter 4: Data sources Chapter 3: Impact of urbanization 24 p. and anthropo- Chapter 2: genic heat Chapter 1: Future scenarios 20 16 p. Cities in changing p. climate 10 p. Executive summary p.6 4 Chapter 5: Urban climate Chapter 6: analysis and Heat wave tools 28 impacts and warning systems Chapter 7: 32 p. Climate adaptation p. measures 38 p. Roadmap for increased resilience to urban heat p.44 References 48 p. 5 EXECUTIVE SUMMARY Executive summary Heat waves and extreme temperatures are an increasing concern for many cities across Europe and globally. Extreme temperatures are among the deadliest hazards in Europe. Between 1980 and 2017, heat waves—extended periods of unusually high atmosphere-related heat stress— accounted for 68 percent of natural hazard–related fatalities among the European Economic Area countries and five percent of economic losses. Direct health impacts of heat are high among vulnerable populations, including children, the sick, and the elderly. Indirect impacts of heat include productivity loss, risk of fires, impact on water resources and agriculture, and power cuts. The increase in the intensity and frequency of heat events is linked to global climate change, which poses a serious challenge for urban areas in Europe.i The UHI effect is a typical feature associated with urban climate that enhances the excessive heat in cities during heat waves, and has negative impacts on people’s health and city functions. The UHI effect results from the interaction of different physical processes. Temperatures are higher in densely built urban areas than in surrounding areas, due to extensive sealed-surface coverage and small share of vegetation. With more than 50 percent of the global population currently living in urban areas, urban land use changes impact local climate and urban air temperatures, and these impacts are enhanced by anthropogenic (industrial and socioeconomic) activities. Reduced air circulation and limited cooling at night contribute to cities being warmer and more prone to excess heat during heat waves than, rural areas, while building materials used in cities facilitate the absorption of solar radiation and thus exacerbate heating. 6 EXECUTIVE SUMMARY Sustainable urban development and climate-resilient spatial planning play an important role for climate change adaptation in urban areas. The intensity of the UHI effect depends on many factors, such as the size and structure of the city; heat emissions from buildings, industry, and vehicles; topography; and climate and meteorological conditions, including airflow. Anthropogenic heat emissions alone, such as waste heat from cooling systems, can locally increase air temperature by an additional 1–3°C. Understanding how land use and climate trends lead to changes to the local climate is critical for future development plans and climate adaptation strategies, and can help decision makers find optimally cost- effective, evidence-based, and consistent solutions for sustainable cities. Many complementary tools are available to help integrate climate information into policy-making and urban planning. Modeling can help us understand urban climate processes for given urban areas and surfaces, and can focus on different spatial scales and terrains. Building-scale models help to inform architectural and engineering design. Micro-scale models are used in construction projects for large building blocks or districts, or open (green) space designs, while city-scale models provide information for strategic urban planning and climate adaptation actions. Simulations can identify critical zones with increased environmental risks, such as hot spots, and can serve to support efforts to mitigate the UHI effect and improve urban climate, through such means as ventilation, greening, air pollution monitoring, and water and energy management. Finally, given that urbanization can lead to environmental changes beyond the local scale, regional-scale models are used to understand processes on different spatial scales and interactions within the climate system. Cities seeking guidance on managing heat waves and the UHI effect can make use of a vast range of data for in-depth analysis. Urban climate analysis can use extensive meteorological observation networks and data sources from remote sensing as well as from so-called citizen weather stations (CWS), set up by citizens or private companies. Crowdsourced data have gained in importance in past years. This trend is expected to continue in the future, as ownership of weather stations connected to the Internet of Things will increase. After quality control, meteorological data measured by CWS can provide results complementary to those of stations belonging to national meteorological services networks. Supported by these tools and data, cities have access to many solutions to mitigate the increasing risk of heat waves and its enhancement by the UHI effect. Adaptation measures broadly fall into two categories: nature-based and technological solutions. Nature-based solutions refer to green city approaches, which increase the coverage of vegetation to provide better cooling and shading, and blue city approaches, which use water for cooling effects. Technological solutions include white city approaches, which use “cool” materials to enhance reflection and reduce the absorption of solar radiation. The success of specific measures depends on local conditions; and in many cases, combining these measures may be most appropriate and bring the highest benefits. Many of these measures also provide multiple benefits, such as space for recreation, increased energy efficiency, and human comfort. Urban climate models can be used to quantify the effect of different adaption options while considering local climate conditions and urban structure. Simulations and scenarios can help identify critical zones in the city in current and future climate and thus support the prioritization of adaptation plans. Furthermore, they can also help evaluate the effectiveness of urban planning measures to reduce the heat load before construction, and support communication and consensus-building among different stakeholders, both of which are critical for the success and sustainability of specific preventive and adaptive measures. 7 EXECUTIVE SUMMARY In parallel to climate adaptation at the city level, improved preparedness and awareness are needed to tackle the risks of heat waves. Heat health warning systems and heat health action plans help to address, Linz manage, and reduce health-related risks. Warning systems include threshold values for issuing warnings, a system of graded alerts, and the communication of the alerts to the general public or target groups. Following recent heat waves, many national and local governments in Europe have implemented heat health prevention plans, which have contributed to saving lives and reducing damage. This report concludes with a roadmap with actions for à p. 29 increased resilience to urban heat. The roadmap focuses 205,613 (2018) on the critical steps that can help decision makers m² 96 km² understand the drivers of heat waves and UHI effects in their city, the scope of risk (including people and assets 8.8 °C exposed), as well as the impacts of heat waves on specific 754 mm areas or population groups. In parallel to other considerations, this critical risk information can form the basis for identifying the most effective use (or combination) of solutions, including green, blue, or white city measures, and for developing and implementing an action plan with agreed actions, investments, and monitoring and evaluation to improve urban planning and preparedness. Klagenfurt Available urban climate analytics and modeling tools can support the overall process for better results. This framework is part of a risk management approach applicable to multiple hazards (such as earthquakes, floods and storms) faced by municipalities. The integration of these concepts can help to minimize climate change and other hazard–related loss to public, private, and combined investments, leading to more sustainable urban à pp. 40; 41 development and planning, and, ultimately, more resilient economies and societies. 100,851 (2018) m² 120 km² Abbreviations 8.2 °C CWS citizen weather stations 885 mm DHMZ Croatian Meteorological and Hydrological Service EEA European Environment Agency HHAP heat health action plan HHWS heat health warning system RCP representative concentration pathway UHI urban heat island WHO World Health Organization WMO World Meteorological Organization ZAMG Zentralanstalt für Meteorologie und Geodynamik (Austrian National Weather Service) 8 EXECUTIVE SUMMARY Kraków Vienna à pp 12; 17 à pp. 19; 25 771,069 (2018) 1,893,779 (2018) m² 327 km² m² 414 km² 7.6 °C 10.2°C 669 mm 620 mm Cluj-Napoca Zagreb Graz à p. 24 322,572 (2016) m² 180 km² 8.3°C 566 mm à p. 39 à p. 12 287,995 (2018) 806,341 (2018) m² 128 km² m² 641 km² 8.7 °C 11.7 °C 838 mm 856 mm Geographic and demographic factors, and climate information for a sample of Central Population European cities. Urban areas are characterized by high imperviousness. Credit: m² Area ZAMG/Kainz based on data for Imperviousness Density 2015 from Copernicus Land Mean annual temperature Monitoring Services (https://land.copernicus.eu/pan-european/high-resolution- Mean annual rainfall layers/imperviousness/status-maps/2015), CRU TS4.01 and ZAMG climatological data for the period 1971—2000 (Harris and Jones 2017; https://climatecharts.net) and city population data (see References). 9 1 CITIES IN CHANGING CLIMATE Urban areas experience more excessive heat than their rural surroundings due to the urban heat island (UHI) effect. Understanding the processes and evaluating possible changes occurring in the local climate is important as the first step for sustainable urban development and climate-sensitive urban planning. Along with key definitions and an overview of the impacts of UHI effects, this chapter provides examples from Zagreb and Kraków focusing on understanding the importance of UHI effects for urban development. CITIES IN CHANGING CLIMATE building materials store solar heat and release it at night anthropogenic heat sources (waste heat from buildings, factories, and vehicles) dark surfaces have higher absorption of increase the heat island effect solar radiation lack of vegetation means less paved surfaces heat up faster and cooling from evaporation prevent intake of rain water in the soil and plant transpiration long-wave radiation is trapped Temperature in street canyons Figure 1. Schematic illustration of the urban heat island effect and factors that contribute to higher temperatures in urban areas. The heat load is typically lower in the rural surroundings than in dense built-up areas. The graphic also illustrates parks, water surfaces, forests, and open spaces that can create cooler areas within the city. Credit: ZAMG/Hollósi. THE DRIVERS OF THE UHI EFFECT in terms of land cover and land vehicles; topography; climate changes—as well as the zone; and meteorological Climate change is one of the additional release of conditions (Oke 1982). In cities most significant environmental anthropogenic heat combined with flat relief, land cover and and societal challenges that the with less vegetation, reduced land use play an important role world is facing today. Cities, air circulation, and reduced in determining spatial along with urban populations nocturnal cooling—contribute temperature differences. concentrated in densely built- to cities being warmer than Analyzing UHI in cities located up areas, are highly vulnerable their surroundings and more in a valley, on a slope, or on a to climate change impacts, such prone to excess heat (Oke hilltop requires more attention as negative consequences of 1978). Urban building materials due to different processes extreme heat events often have high heat capacity caused by complex terrain. (Rosenzweig et al. 2011). In and thermal conductivity, Topography affects the local addition to an observed enabling a greater absorption wind conditions and has an warming trend, the so-called of solar radiation. Retained impact on temperature UHI effect is a typical feature heat is then released during the inversion in height. Therefore, associated with urban climate, night as long-wave radiation, the UHI can either be which further enhances the but the cooling is slowed due to weakened or strengthened. excessive heat in cities. The UHI urban structures. The intensity Additionally, the UHI has effect results from the of the UHI depends on many strong temporal variations interaction of different physical factors: the size and structure dependent on climate processes (Figure 1). The of the city; anthropogenic conditions and human modifications of energy balance emissions related to waste heat activities. Studies in Central in the built-up environment from buildings, industry and Europe show that maximum 11 CITIES IN CHANGING CLIMATE UHI values developed at night partly because of the land higher-vulnerability groups. and do not show a relationship cover. On a hot summer day, Overheating of buildings to the city size (Santamouris dry urban surfaces placed in during prolonged heat waves 2007). Maximum UHI intensity direct sunlight can be up to and associated negative varies between 1–12°C and the 25–50°C hotter than the air impact on residents have been highest values correspond to (Berdahl & Bretz 1997), while identified as a public health anticyclonic periods of the temperatures of shaded or issue (Figure 2), as extreme weather, while much larger moist surfaces remain similar temperatures are considered variations (more than to that of the air. The UHI can among the deadliest hazards in 10–15°C) are rarely observed have secondary impact on Europe (WMO 2014). Cities in due to local wind circulation local meteorology, including particular are susceptible to reinforcement that mixes air the modification of local wind heat-related health impacts and limits the extent of UHI. patterns; and due to because of the high density of Weather factors that have the convection provided by extra population, with many people largest influence on the UHI heat, additional shower and exposed to high temperatures intensity are wind speed and thunderstorm activity can be over a long period. The UHI cloudiness. If incoming solar greater than usual (Shepherd effect during heat waves leads radiation is decreased by 2005). The influence of UHI on to a low recovery potential, clouds, temperature ecosystems has been observed particularly due to high differences and therefore UHI as well, e.g., extension of the nighttime temperatures and intensity are also subsequently growing season (about 15 insufficient cooling. Direct decreased. Such weather additional days) in urban areas impacts of heat on human conditions help to improve compared to the surroundings health can range from fatigue human thermal comfort both in (Dallimer et al. 2016). and discomfort to heat the city and in surroundings. cramps, heat exhaustion, Humidity plays an important HEAT-RELATED RISKS AND IMPACTS heatstroke, and death. The role as well. Cities in regions effort of the human body to with variable wet and dry Urban residents are exposed release heat and keep the seasons have larger to high heat-related risks in a body temperature around temperature differences during changing climate. Besides 37°C puts an extra strain on the dry period. Due to their experiencing the effects of the cardiovascular system small share of vegetation, built- global temperature rise, they (Havenith 2005), which can up areas also have less water experience local temperature aggravate existing health evaporation, which contributes increase due to the UHI effect. conditions. Apart from these to increased surface and air In order to determine long- direct impacts, indirect temperatures. The UHI term changes in heat load, impacts are also possible: e.g., phenomenon refers either to many factors need to be an increase in accidents, labor differences in air temperature considered, such as historical productivity losses, increased at two-meter height development, modification in risks of forest fires, impacts on (atmospheric UHI) or to surface urban structure, increase in water resources, transport temperatures (surface UHI). population, and related restrictions, agricultural losses, Surface temperatures vary anthropogenic heat and power cuts (UNEP 2004). more than air temperatures production or changes in Regarding the health effect of during the daytime and tend to weather patterns. Given that heat waves, particularly be greater when the sun is global and regional warming vulnerable groups include the shining. Due to seasonal are leading to more frequent elderly (Fouillet et al. 2006), variations in the solar radiation, and more intense extreme hot due to changes in their the magnitude of surface UHI periods, heat can already be thermoregulatory system shows greater intensity in the considered as a severe hazard (Kovats & Hajat 2008; WHO summer period, for people in 2011), as well as infants, 12 CITIES IN CHANGING CLIMATE whose thermoregulation is still since the living space cannot numbers of deaths due to heat immature and whose be kept cool. Social isolation waves can be expected to dependency level is high (WHO may lead to a delay when help increase if no measures are 2011). In addition, workers or medical care is needed taken. who might be exposed to (Casanueva et al. 2019). Loose extreme heat all day, as well as social contacts and a large PREVENTING HEAT IMPACTS pregnant women, people with number of single and lone- chronic diseases, and sick and pensioner households in cities Early warning systems, poor people, are at high risk constitute an additional risk. awareness and appropriate during heat waves. Housing As climate change makes heat spatial planning can reduce conditions and social isolation waves more frequent and negative impacts of heat are additional risk factors. intense, as cities grow, and as events. For more information, Living in a poorly insulated the population in many see Chapter 6 on heat warning building or on the top floor can countries ages appreciably systems and Chapter 7 on aggravate the situation and over the next 50 years climate adaptation measures. poses additional risk factors, (Confalonieri et al. 2007), the DIRECT AND INDIRECT IMPACTS VULNERABLE POPULATION GROUPS Heat illness - Dehydration - Heat cramps and stroke Accelerated death from: The less abled, pregnant, Children and - Respiratory, cardiovascular, or or already infirm the elderly other chronic diseases Hospitalization: - Respiratory and renal disease - Stroke and diabetes mellitus The poor, displaced, Outdoor Athletes - Mental health conditions and homeless workers Health services: - Increased ambulance call-outs - Slower response times - Increase in hospital admissions Potential disruption of infrastructure - Power, water, transport, productivity Increased risk of accidents: - Drowning - Work-related accidents - Injuries and poisonings Environmental impacts: - Air pollution - Ecosystem (plants, animals, microorganisms) - Drought - Forest fires Figure 2. Direct and indirect health effects and the population groups most vulnerable to extreme heat. The extent and form of the impacts depend on (among other things) the timing, intensity, and duration of the extreme heat event; the level of adaptability of the population; and possible actions taken to prevent negative effects of heat. Credit: ZAMG/ Hahn and Hollósi, based on WHO, “Information and Public Health Advice: Heat and Health”, https://www.who.int/globalchange/publications/heat-and-health/en/. 13 CITIES IN CHANGING CLIMATE Example from Zagreb Zagreb is the capital and largest city of Croatia, as well as popular tourist controlled by the city’s topography (Nitis et al. 2010) and morphology destination especially in the resulting in intense summertime summer months. Zagreb’s climate is land surface temperatures (Kovacic continental with maritime 2014). Atmospheric circulation influence. The 20th century has (particularly upslope and seen a warming trend with an downslope wind patterns forming increase in mean annual at the slopes of the nearby temperature of +0.07°C per decade. mountain Medvednica during the The warming of Zagreb has become summer anticyclonic conditions) more pronounced in the last can alter thermal stress and air decades (MZOIP 2010). Between quality in urban areas (Klaic et al. 1901 and 2008, the majority of 2002). The local UHI-induced warm temperature indices (e.g. circulation directed toward the city summer days, warm nights) had an center can be strengthened in the upward trend, while a majority of late afternoon due to the increased cold temperature indices (e.g. frost urban-rural temperature difference. days) had a downward trend. The This local circulation effects the 806,341 641 km2 observed trend in heat load can be downslope thermal circulation by (2018) attributed to regional climate enhancing the upward air warming, but also to urbanization movements on the southern and the associated UHI effect. The hillsides, and further contributing to 79.4 15.6 tropical nights UHI formation in Zagreb is generated thermal stress. summer days Example from Kraków Kraków, Poland, is located in the valley of the Vistula river with in vegetation and weather conditions. Despite relatively small diversified relief and land cover. height differences (about 100 m), Like many cities in Central Europe, relief is an important factor Kraków developed around the influencing urban climate in historical center, and its Kraków, as it forces the formation infrastructure has gone through of a cold air lake in the valley floor intensive spatial development in (outside densely urbanized areas) the second half of the 20th century. and air temperature inversions Land surface temperature, mapped (Bokwa et al. 2015). The cluster through satellite imagery, indicates analysis of air temperature that hot locations are mainly in the measurements, conducted between city center, along the main 2009 and 2013 in 21 urban and rural transport arteries and industrial locations across various landforms, zones (Walawender et al. 2014), shows several types of nighttime while cold locations include forests, thermal structures, including city parks, and water reservoirs. elements that display the formation Although highly dependent on land of the inversion layer, cold air cover types, the thermal structure is reservoir, and the UHI peak zone. 771,069 327 km2 influenced by additional factors, (2018) such as emission of anthropogenic heat, insolation of the surfaces 56.4 0.6 depending on land relief and shape summer days tropical nights of buildings, and seasonal changes 14 CITIES IN CHANGING CLIMATE 120 105 1968 Heat load in the city of Zagreb Annual number of 90 summer days 75 shows a warming trend, 60 especially for nighttime 45 30 temperatures in the city center, 15 as well as expansion of areas 0 with excessive heat caused by urbanization (Figure 3). Expected 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Punt ij ar ka G ric Maks imir Pleso regional warming together with 50 2012 potential expansion of the city could contribute to the Annual number of 40 tropical nights 30 intensification of UHI, increased thermal stress, and air pollution 20 in Zagreb, making UHI a serious 10 environmental problem. 0 Sustainable urban planning and development is needed for 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Punt ij ar ka G ric Maks imir Pleso Tmax Zagreb, building on an 24 25 26 27 28 29 30 31 32 33 understanding the parameters and processes contributing to Figure 3. Left: Time series of climate indices in Zagreb (summer days, Tmax ≥25°C; UHI intensity and possible tropical nights, Tmin ≥20°C) showing a warming trend. Source: DHMZ, https://meteo.hr. Right: Spatial variability in daily maximum temperature (Tmax ) based on the urban mitigation strategies. climate model and land use data from the year 1968 (top) and 2012 (bottom). Note expansion of areas with excessive heat caused by urbanization. Source: CroClimGoGreen Project, Zagreb, Croatia, https://www.pmf.unizg.hr/geof/znanost/klimatologija/ccgg. The atmospheric UHI of cities located on variable landforms with diverse land cover is characterized by a complex thermal structure, which results from the interaction of urban energy balance and processes induced by the relief. The terrain-induced processes may also include upward or downward wind flows or air temperature inversions. Krakow is one of the cities which displays such characteristics. Figure 4 shows hot and cool areas in Kraków. The air temperature changes rapidly during the day and the UHI is one of the urban Figure 4. Thermal stability (SD) based on surface temperature in the agglomeration climate elements contributing to of Kraków (shaded relief in the background). Characteristic cold and hot spots: (A) temperature variations. water reservoirs of former gravel excavation sites in Przylasek Rusiecki, (B) Wolski Forest, (C) Rakowicki Cemetery, (D) “Krokus” Shopping Center, (E) Kraków Old Town, (F) steelworks in Nowa Huta, and (G) slag heap in Pleszow. Source: Walawender et al. 2014. 15 2 FUTURE SCENARIOS A key step in understanding UHI effects is to consider future scenarios. Global temperatures are projected to increase by 3–6 °C by the end of the century if greenhouse gas emissions continue to rise. Depending on the emissions and global climate development, the heat load in urban areas is expected to increase further. This chapter highlights key projections, and provides an example of future projections for Kraków. FUTURE SCENARIOS Figure 5. Stylized global mean temperature anomalies from 1860 until 2200. The future development depends on the climate action scenario: decisive climate policy reducing greenhouse gas emissions limits warming, whereas temperatures will continue to rise under the worst-case scenario RCP8.5. Credit: Hawkins and Radtke. GLOBAL CLIMATE PROJECTIONS Intermediate scenarios, increase further in the future RCP4.5 (Thomson et al. 2011) (Stocker et al. 2013). Toward The Earth’s future climate and RCP6.5 (Masui et al. the middle of the century, the depends strongly on the 2011), are consistent temperature’s increase development of greenhouse (respectively) with emissions compared to 1986–2005 is gas emissions. Several peaking in 2030 under an estimated to be 1.4°C under scenarios describing future active climate change scenario RCP4.5; the estimate emissions consistent with mitigation scenario, and in for the worst-case scenario is various socioeconomic 2070 under a limited climate 2.0°C. For the end of the assumptions are available, change mitigation scenario. century, these numbers are describing a range of climate These assumed climate 1.8°C and 3.7°C respectively. outcomes (Figure 5). These so- scenarios form the basis of Except under RCP2.6, warming called representative climate projections. Such will continue beyond 2100. concentration pathways projections are based on However, the climate does not (RCPs) extend from RCP2.6 numerical simulations change uniformly around the (van Vuuren et al. 2011), performed using climate globe. Indeed, the annual consistent with decreasing models and describe the average land temperature over greenhouse gas emissions Earth’s climate in future Europe is projected to increase after 2020 (decisive climate decades. Since the late 19th more than the global mean action), to RCP8.5 (Riahi et al. century, global mean surface (Collins et al. 2013). To study 2011), in which greenhouse temperatures have been regional climate in more detail gas emissions continue to observed to increase; and for and at a finer scale, regional increase under a worst-case all scenarios, global mean climate models are used to scenario. temperatures are projected to 17 FUTURE SCENARIOS Figure 6. Global – regional – local: A chain of different climate models is used to downscale coarse global results to urban scales, increasing the spatial resolution from 100 km to 100 m in order to capture the increase in the number of the summer days on a finer scale. Credits: ZAMG/de Wit and Kainz. downscale results from make it possible to study the scenarios can be projected. general circulation models implications of climate The following example shows representing the global scale change for the heat load at the development of the urban (Figure 6). For Europe, the city scale, they also help heat load in Kraków, Poland, EURO-CORDEX initiative (Jacob identify the spatial distribution under RCP4.5 (intermediate et al. 2014) provides a suite of of the heat load under current scenario) and RCP8.5 (worst- regional climate projections climatic conditions, thus case scenario). Using the with a spatial resolution of 12 revealing potential hot spots. To ensembles of regional climate km. These simulations, in turn, define the spatial pattern of simulations from EURO- form the basis for urban heat load at urban scales, CORDEX as a base, the heat climate simulations at even climate indices such as mean load expressed by the mean higher resolution. annual number of summer annual number of summer days (days with maximum days is determined for the FUTURE URBAN CLIMATE temperatures exceeding 25°C) reference period (1971–2000), can be used. Using specific the near future (2021–2050), Urban climate models, such as methods (e.g. the cuboid and the end of the century MUKLIMO_3 (Sievers 2016), method from Früh et al. 2011), (2071–2100). can be used for a wide range the long-term aspects of urban of applications. They not only heat load for different climate 18 FUTURE SCENARIOS In Kraków, between 1971 and 2000, scenario (for the period 1971–2000 the mean annual number of it was 17.6 days). For the period Example fr om Kraków summer days was about 60 2071–2100, the mean values vary (between 1981 and 2010, it was 66) from 36 days for RCP4.5 to 57 days in the most densely urbanized for RCP8.5). For both future climate areas, whereas it was below five periods, the spatial pattern shows the impact of land use/land cover as .5 P8 days in forested areas located RC within the city borders (Figure 7). In well as relief on the thermal rural areas, large differences are conditions. The highest heat load is also seen between valleys and in densely built-up areas located in nearby hilltops. The heat load in the the valley floor, and in urban areas valleys is significantly higher than in located close to Kraków’s borders. the elevated areas (Bokwa et al. Green urban areas located between 2018). The climate change scenarios heavily urbanized city parts show a for the near future (2021–2050) smaller number of summer days 5 show a slight increase in the heat than in the built-up areas. RCP4. load. The mean annual number of summer days is expected to increase by about 10 days, reaching a total of about 30 days for the whole domain, regardless of the RCP2.6 “Worst-case” climate change scenario (RCP8.5) “Active mitigation” climate change scenario (RCP4.5) 1971–2000 2021–2050 2071–2100 Figure 7. Mean annual number of summer days in Kraków for 1971–2000 (left) and future climate projections for the time period 2021–2050 (center) and 2071–2100 (right) using the model simulations for the RCP4.5 (bottom) and RCP8.5 (top) scenarios. Source: Adapted from Bokwa et al. 2018. 2.5M – 2.0M – 1.5M – 3 1.0M – 0.5M – IMPACT OF URBANIZATION AND ANTHROPOGENIC HEAT This chapter focuses on demonstrating how urbanization and anthropogenic heat contribute to UHI effects. Greater built-up of urban areas leads to more energy consumption and can negatively affect the local climate. In light of climate change, sustainable urban development and reduction of anthropo- genic emissions are required, as shown with an example from Vienna. IMPACT OF URBANIZATION AND ANTHROPOGENIC HEAT Example fr om Vienna URBAN SPRAWL Figure 8. Degree of imperviousness in SOIL SEALING Vienna (left) and effect of urbanization on temperature extremes. Two examples with sealing of all open spaces in existing urban environment (bottom) and urbanization based on a new city development plan (top) show an increase in daily maximum air temperature on a hot day by 2°C due to urban construction and reduction of vegetation. Source: Green.Resilient.City; Kainz et al. 2019a. UHI EFFECT AND CITY GROWTH heat load, which in the future strategies and facilitate is expected to superimpose on selection and implementation Modification and changes in regional climate warming of climate adaptation options. land use and land cover play (Guerreiro et al. 2018; Smid et an important role in al. 2019). To understand the URBANIZATION IN VIENNA determining local climate role of long-term land use characteristics (Oke 1973; changes in cities and help The city of Vienna is projected Landsberg 1981). They affect estimate changes in thermal to grow, with a total increase new developing areas as well conditions resulting from in population of 289 thousands as the existing urban regional climate change and (+15.5 percent) during the environment, where building urbanization, it is useful to period 2018–2048 (Bauer et al. construction and increasing combine high-resolution urban 2018). The city is urbanizing soil sealing can lead to climate model simulations rapidly and this is evident in intensification of the UHI using historical and future land the densification of the effect. Based on observational use data with climate existing built-up areas and time series data from the 20th information. Modeling the sprawl of the city toward the century, an obvious warming effects of new buildings and northeast and southeast trend due to urbanization was level of imperviousness on (Figure 8). The following already recorded in many urban temperature provides examples show the effect of cities (Chrysanthou et al. useful information regarding urbanization on the spatial 2014). City growth—both in future urban plans and may distribution of heat load, both terms of densi-fication and serve as a scientific basis to historically and relative to urban sprawl—induces higher optimize spatial development 21 19 IMPACT OF URBANIZATION AND ANTHROPOGENIC HEAT 18TH CENTURY TODAY HYPOTHETICAL CITY GROWTH 4cyerge_ts US 51 02 52 03 53 04 54 05 55 06 56 07 57 08 58 09 Figure 9. Building distribution in Vienna (top) and modeled mean annual number of summer days (Tmax ≥ 25°C) in Vienna (bottom). The bottom maps use climatological data for the period 1981–2010 based on historical maps of the First Military Mapping Survey of the Austrian Empire, from the period 1764–1787 (left), a current land use survey provided by the Vienna city administration (center), and hypothetical city growth in the northeast and southeast (right). Adapted from Zuvela-Aloise et al. 2013, 2014. future development plans. be attributed to the city (i) the new developing area of The relationship between growth and is comparable to Aspern Seestadt in the east long-term modification in observational data from to the and (ii) further soil sealing in urban climate and large-scale period prior to year 1850. the densely built-up area south urbanization was investigated These results illustrate the of the city center. The by modeling the spatial long-term consequences of modeling results show that in distribution of heat load urbanization. In the future, if case no greening is planned in based on current urban the city were to follow a new construction or all green structure and land use data similar rate of urbanization, and open spaces are paved in reconstructed from the the urban heat load could be the existing urban geographical maps of the expected to be largely spread environment, the maximum air period 1764–1787; see Figure on the surrounding rural temperature on a hot day will 9 (Zuvela-Aloise et al. 2014). environment. Due to the inter- be higher (Reinwald et al. The modeling results indicate action of land use and local 2019). Aspern Seestadt is one that the intensity of the UHI in wind conditions, neighboring of the largest urban the historical city center might city areas might experience development projects in have been similar to today’s more extreme heat as well Europe, and therefore the values due to the high-density (Zuvela-Aloise et al. 2013). On planning process is putting built-up construction with a short time scale, which special emphasis on sustain- fortification walls. The spatial considers many building able and green building, and structure shows a complex projects in planning, avoiding energy efficiency. It can thus thermal pattern as a response worst-case scenarios is of serve as a role model for to exerted land use crucial importance. This is future sustainable urban modification and reveals illustrated by two case studies development (www.aspern- expansion of areas with of future city development: seestadt.at). excessive heat load; this can 22 01 AIR CONDITIONER USAGE IN CITIES INCREASES Due to rising temperatures and prolonged heat wave events, high demand for cooling of indoor spaces has arisen. ANTHROPOGENIC HEAT 03 02 The formation of UHIs is not ENERGY DEMAND only due to a city’s fabric and INCREASE OF CLIMATE INCREASES geometry. Heat emitted by CHANGE AND UHI EFFECT The growing use of air human activities—such as Air conditioning systems conditioners in homes and further add to the UHI effect offices around the world is cooling or heating of buildings, as the waste heat generated expected to be one of the industrial processes, and by these systems increases top drivers of global transportation—also plays a local temperatures in electricity demand built-up areas. over the next three key role (Figure 10). These decades. anthropogenic heat emissions can increase air temperatures Figure 10. Anthropogenic heat feedback by approximately 1–3°C (Ma et cycle. Credits: ZAMG/Hollósi and de Wit. al. 2017). Although during times of peak energy anthropogenic heat emission is consumption, and thus puts generally larger in winter, the additional strain on the power negative impact is strongest in grid, making it more summer during heat waves, vulnerable to power outages when already high or blackouts (Steininger et al. temperatures are being 2015). Furthermore, if this increased even further. One of increased energy need is the summer sources of covered by electricity anthropogenic heat emissions generated by the burning of is air conditioning systems. fossil fuels, then it contributes Although they improve indoor directly to climate change conditions through cooling, air through the increased conditioning systems can emission of greenhouse gases. negatively influence the To adapt to increased outdoor urban microclimate temperatures in a sustainable due to their emission of waste way, it is important to consider heat in the urban canyon. cooling solutions that do not Modeling studies have shown lead to further greenhouse gas that during prolonged heat emissions (Matthies et al. periods, air conditioning usage 2008) and to limit the can increase urban air anthropogenic heating of the temperatures up to 3°C locally urban fabric while at the same (de Munck et al. 2013). Sales time guaranteeing indoor of air conditioners have thermal comfort. Improved increased dramatically over building insulation or the use the last few years (Davis et al. of smart shading solutions can 2015). This increase, primarily help reduce solar gain, thereby driven by sales in middle- keeping buildings cool and income countries, is explained decreasing cooling needs. Cool by rising temperatures as well roofs, green roofs, and vertical as income growth. In addition gardens have also been shown to adversely affecting the to reduce indoor air urban microclimate, this rise in temperatures. An additional air conditioning adoption advantage of these measures results in increased energy is their positive cooling effect need, especially on hot days on the urban microclimate. 4 DATA SOURCES Having considered climate change projections, urbanization and anthropogenic heat, this chapter highlights some of the data which can help cities better analyze UHI effects. Extensive meteorological observational networks and different data sources from remote sensing and citizen weather stations can be used for urban climate analysis. Examples of the use of various data sources include Cluj-Napoca and Vienna. DATA SOURCES meteorological parameters such as radiative components or air turbulence and can be adjusted to record data in shorter time intervals. These alternative observational sources have higher spatial density than traditional monitoring networks, but are more limited in duration of measurements than traditional networks, which are operational at all times. REMOTE SENSING DATA Among data sources that may be used to visualize relative Figure 11. Satellite image and tree cadastre, building footprints, and height layers (using hot and cold surface spots are photogrammetry) in the area of the Viennese public park Prater. Source: City of Vienna. satellite data. Surface UHI studies based on remote MONITORING NETWORKS variations, dense monitoring sensing data have been station networks are needed. conducted for several decades Urban climate effects are However, the establishment of (e.g., Pongrácz et al. 2010). generally investigated by an appropriate operational Examples include observations examining the differences in monitoring system with high- with the MODIS instrument meteorological elements quality equipment is often aboard the Terra and Aqua measured and observed in very cost-intensive, and other satellites, which provides land rural and urban areas. Long- sources of information can be surface temperature term monitoring records, for helpful to fill the data gaps. observations with a spatial several decades or more, are Recent trends show that resolution of one km, or particularly important in utilizing alternative networks Landsat EMT+ data with a 60 climate analysis in order to of citizen weather stations m resolution (e.g., LANDSAT- appropriately capture (CWS) can provide promising 8). Even higher spatial temporal variability. National supplemental information for resolutions can be obtained weather services operate urban climate analysis with airborne thermal imaging monitoring networks and (Chapman et al. 2017). In using aircrafts or automated provide essential order to evaluate specific flying devices. The remote meteorological data (e.g., on aspects of urban climate, sensing data provide many air temperature, wind, observations can also be made important insights into the humidity, precipitation), which within the scope of spatial structure of UHI, are also available on European measurement campaigns especially in areas with low- scale (van Engelen 2008). Due using fixed or mobile stations, density monitoring networks. to the diversified urban fabric, like temperature sensors Beyond meteorological simple urban-rural gradients attached to transport vehicles observations, diverse satellite- are often not sufficient to (Brandsma & Wolters 2012; based products that provide evaluate the urban climate and Yokobori & Ohta 2009). Such imagery of urban structures, microclimatic differences measurements can be land cover, and biophysical found within the city area. For designed to investigate characteristics are extremely the investigation of small-scale additional 25 DATA SOURCES important in understanding processes, such as the relationship between vegetation and surface Example from Cluj-Napoca temperature (Guha et al. 2018). Ongoing developments in technology have led to several projects and programs that aim to overcome the weaknesses of existing land cover and land use data sets and offer improved spatial and thematic services on regional, national, and European scales. Products of Copernicus Land Monitoring Services, (https://land.copernicus.eu) 322,572 180 km2 the European Environmental (2016) Agency, etc. can support cities with harmonized information 64.2 0.2 in order to make them more summer days tropical nights resilient and sustainable. In recent years, through their The thermal conditions in Cluj- open data policies, several Napoca, Romania’s second-most populous city, have been analyzed cities have made high-quality based on satellite imagery (Herbel 3D information accessible et al. 2018). The highest surface to the public; see Figure 11 temperatures are found in urban for the example of Vienna. areas and are related to local land Despite the many advantages use characteristics. Satellite data of remote sensing on land use and land cover, such as products provided by Copernicus observations, which enable Land Monitoring Services, can investigation of cities’ spatial provide complimentary Legende Imperviousness (%) patterns and thermal information to guide sustainable <10 10 20 30 40 50 60 70 80 90 characteristics, researchers urban planning (Figure 12). still face challenges in using satellite data for urban climate analysis (e.g., limitations in case of cloudiness, as well as in spatial resolution or temporal availability). It is important to note that satellite-derived thermal data obtain surface Tree cover density (%) temperatures instead of air Grassy and non-woody vegetation Water <10 10 20 30 40 50 60 70 80 90 temperatures; these can be Tree cover density (%) Grassy and non-woody vegetation Water <10 10 20 30 40 50 60 70 80 90 markedly different, so the Figure 12. Cluj-Napoca spatial data available from Pan-European data sets: interpretation of the results Urban Atlas 2012 (bottom left), Tree Cover Density 2015 with green and water must be done carefully areas (bottom right), and Imperviousness Degree 2015 (top right) of EEA and (Tomlinson et al. 2011). Copernicus Land Monitoring Services, available at: https://land.copernicus.eu/pan-european. 26 DATA SOURCES ALTERNATIVE DATA SOURCES Example from Vienna Although the UHI intensity may be determined by comparing urban and rural air temperature measurements, for a detailed investigation of the spatial heat load pattern more observations are necessary. However, even in cities with a relatively dense observational network, additional data sources are needed for high-resolution urban heat load studies. Urban climate models are among the available tools to obtain high- 1,893,779 414 km2 resolution information; (2018) however, they need to be 64.1 4.0 validated, and various obser- summer days tropical nights vational data sources may be used as an alternative to non-CWS reference stations. In traditional meteorological Quality-controlled, crowdsourced CWS air temperature observations Vienna, 1,357 unique stations were observational networks. One were used to study the temperature available during the study period, of example is the use of crowd- distribution in Vienna, Austria, for which 1,083 stations passed the full sourced data from CWS (Figure an 11-day high-temperature period quality control procedure. This 13). The unknown quality of in August 2018 (Feichtinger et al. represents a major improvement in these measurements is 2020). The statistical quality control the spatial resolution of available was based on the procedure temperature data compared to the compensated for by the large developed in a previous study currently available operational number of available obser- (Napoly et al. 2018), further network. The quality-controlled vations, which impose a optimized by incorporating two CWS are comparable to the urban stringent statistical quality additional steps to address the climate models simulations and control. Crowdsourced data specific issue of radiative errors provide a valuable data source for have recently gained importan- using solar radiation data from further studies. ce in urban climate research (Meier et al. 2017), and this trend is expected to continue, as ownership of weather stations connected to the Internet of Things is expected to increase. After application of the quality control, CWS meteorological data provide results comparable to those of national meteorological service networks, and discrepancies Figure 13. Spatial distribution of air temperature in Vienna, on August 17, 2018, between these data sets could at 00:00 UTC, based on MUKLIMO_3 model simulation (left) and be explained by differences in CWS measurements (right) based on Feichtinger et al. 2020. station location relative to the urban structure. 27 5 URBAN CLIMATE ANALYSIS AND TOOLS Building on the information about various sources of data available to improve UHI analyses, this chapter presents the key numerical models and tools that can be used to analyze urban climate and to support integration of climate information in urban planning. Advanced modeling approaches for the city of Linz are included as an example. URBAN CLIMATE ANALYSIS AND TOOLS Research studies on UHI are architectural and engineering City-scale models enable the characterized by a large variety design (e.g., Reinhart & Davila analysis of atmospheric and of methodological approaches 2016). However, these models surface processes covering the depending on the focus of can be applied only to an area of an entire city. They can interest. Investigations aim to isolated building volume and thus meet specific needs for understand the neglect the influence of strategic urban planning and comprehensive processes of neighboring areas and development of climate the UHI phenomenon both in surroundings on building adaptation strategies on a space and time. performance. higher regulatory level than individual urban projects (e.g., MODELING APPROACHES Micro-scale models are widely Sievers 2016). Simulations employed to represent the carried out by city-scale Numerical modeling is a interaction of resolved models can help to identify fundamental tool for buildings with their critical zones in the city with understanding urban climate surrounding environment. In increased environmental risks, processes, such as the most applications, the impacts such as hot spots, and can exchanges of energy, mass, of different parameters—such serve to support urban-scale and momentum within the as building orientation, surface UHI mitigation policies. These urban boundary layer or at the materials, vegetation and tree include evaluation of urban urban surface. Urban climate planting scenarios, human climate for protection of model simulations allow an comfort, and urban ventilation pathways, greening analysis of urban climate ventilation—are investigated. plans, air pollution monitoring, under future urban and/or These models are especially and water and energy climate development useful for the planning of management. scenarios, and can help urban building construction projects planners to find optimally cost- or the design of open spaces. Regional-scale models in effective and science-based They are, however, limited in recent years have solutions for sustainable and spatial extent, covering areas implemented higher spatial future-oriented cities. There is ranging from several building resolutions and can be used to a wide spectrum of models in blocks to a whole district (e.g., investigate urban climate on terms of spatial scales and Bruse & Fleer 1998; Matzarakis short and long temporal applicability to various et al. 2007). Larger-scale scales, including variations in problems (e.g., Grimmond et applications often involve climate forcing and land use al. 2010, 2011). extensive computational costs. changes. These models parameterize urban processes Building-scale models can to include the provide insight on the energy balance of construction materials and anthropogenic heat fluxes for buildings. They are commonly used in URBAN CLIMATE ANALYSIS AND TOOLS modifications in energy balance SPATIAL-TEMPORAL BEHAVIOUR significantly related to building (Masson 2000; Salamanca et al. characteristics, imperviousness, 2010) and due to these It is well documented that the and green surface fractions. simplifications are often less UHI effect can significantly vary Green and water areas can suitable for the evaluation of in space and time (Oke 1995; effectively reduce the intensity specific urban development Oke et al. 2017). Temperature of UHI and amplitude of daily plans. However, they provide heterogeneity of urban areas variations due to shadowing exceptional opportunity to can be explained by the and thermal inertia. However, understand processes on heterogeneity of surface water surface might have different spatial scales and variations, morphology, or reverse effect if they are interactions within the climate human activities (Chapter 1). warmer than the environment. system, such as feedbacks The meteorological situation During the daytime, the intra- between the atmosphere, soil, (e.g., cloudy and windy condi- urban variability can mainly be water bodies, wind circulation tions) has an immediate impact determined by the absorption patterns, and anthropogenic on UHI development, while of solar radiation by various emissions. some features (e.g., effect of urban surfaces, differences in In seeking to fully understand solar radiation) can be delayed wind velocity, and shadowing and describe the UHI due to inertial effects (Figure effects. At night, open spaces phenomenon, it is important to 14). Several studies analyze cool faster, whereas dense understand that no single variations of both air and building areas and urban method is sufficient for all surface UHI in the context of canyons cool more slowly due applications, and that these changes in land use and land to the aggregated heat load techniques and tools have to be cover characteristics. In evalu- and the trapping of outgoing considered as complementary ating spatial behavior, the long-wave radiation through approaches (Mirzaei 2015). intra-urban variability in UHI is the small sky view factor. Figure 14. Spatial and temporal variability of the UHI in Vienna on the hottest day of the heat wave of 2015 (August 12) at 100 m horizontal resolution (clocks show Central European Summer Time). Adapted from Bokwa et al. 2019. 30 URBAN CLIMATE ANALYSIS AND TOOLS AIRFLOW (UHI circulation) are of windward side can be blocked particular importance, as they due to buildings. Therefore, it The heat exchange between create a country-to-city is of crucial importance to buildings and air can change gradient with increased fresh consider ventilation zones for the intensity and patterns of air supply and provide a better long-term urban planning. airflow in urban areas. Wind air quality, especially in Apart from its UHI mitigating patterns are also affected by densely built-up areas. In effect, wind can generate canyon-like structures as well addition, orography or other discomfort and safety issues as by high-density built-up topographic configurations, for pedestrians. In recent areas, where the surface such as coastal areas or river years, human wind comfort roughness is relatively high. valleys, play a significant role became an important factor in These phenomena lead to in inducing local wind systems planning and creating more reduced airflow in urban areas (Figure 15). Different comfortable and functional that can strengthen the UHI topographic settings can buildings (e.g., Janssen et al. effect. Prevailing wind and reduce but also magnify the 2013). High building local air circulation are intensity of the UHI circulation constructions and complex considered important factors in as well, regulating the effects forms as well as funnel-like the mitigation of the negative on air temperature and the gaps between buildings or effects of UHI. In atmospheric dispersal of pollutants parallel rows of smooth-faced conditions characterized by positively or negatively in buildings can increase high temperatures and low urban areas. If a city is located gustiness at pedestrian level wind speed, thermally induced at the base of a slope, for and produce problems of wind local circulation systems example, the cool air on the discomfort around buildings. Example from Linz Relief plays a significant role in the development of local wind systems, as illustrated in the city of Linz, Austria. Figure 15 shows the formation of a nocturnal cold airflow along a valley to the north of the city as a consequence of its terrain structure. The so-called Haselgrabenwind (drainage flow from the Haselgraben valley) has been studied in detail (Mursch- Radlgruber 2003). It shows a specific airflow and wind behavior, with high peaks of wind speed during the first half of the night supporting fresh air movement in the urban area. 205,613 96 km2 (2018) Figure 15. Formation of a nocturnal cold airflow along a 55.8 0.5 valley to the north of the city of Linz based on a model summer days tropical nights simulation using the urban climate model MUKLIMO_3. Adapted from Kainz et al. 2019b. 31 6 HEAT WAVE IMPACTS AND WARNING SYSTEMS Heat waves can have severe impacts on human health. A better understanding of UHI also considers the preparedness and response aspects to excess heat. With various examples across Europe, this chapter provides an overview for heat health warning systems and heat health action plans, both of which can help cities to address, manage, and reduce the health-related risks. HEAT WAVE IMPACTS AND WARNING SYSTEMS HEAT WAVE sweat (Havenith 2005; Figure vapor pressure, and short- and 16). When the air temperature long-wave radiant fluxes on A heat wave is an extended is high, the main way to lose human physiology (Di Napoli et period of unusually high heat is through sweat al. 2019). Other indicators, atmosphere-related heat production and evaporation. such as physiological stress, which may have This cooling effect is equivalent temperature (PET) adverse health consequences compromised in humid and perceived temperature for the population. Heat is not conditions (WHO 2004). (PT) or apparent temperature, only important during the Therefore, indices to describe can be used to evaluate daytime, but also during the thermal comfort usually consist human comfort as well night, as it can lead to a of combinations of dry-bulb (Matzarakis & Amelung 2008). cumulative build-up of heat temperature and different load with little respite during measures for humidity, wind, Figure 16. The parameters that effect the night. Currently, there is no and/or radiation. outdoor thermal comfort. universally accepted definition Credit: ZAMG/ Hollósi; adapted from Havenith 2005. of heat waves (Perkins & CLIMATE INDICATORS Alexander 2013; Robinson 2001), but in general they are The thermal health hazard can periods of at least two or three be assessed using the Universal days with unusually hot Thermal Climate Index (UTCI). weather, which can adversely This index represents the affect human and natural human body’s discomfort to systems (WMO & WHO 2015). thermal stress. It is elaborated Air temperature alone with as an equivalent temperature reference to maximum and via an advanced model of minimum temperature may be human thermoregulation that, reflected diffuse sufficient to define heat waves, coupled with a clothing insula- radiation radiation but it is generally not a tion model, estimates the effect representative indicator of the of wind speed, water human thermal environment. direct HUMAN COMFORT FACTORS radiation sweat Human thermoregulation, and evaporation in particular the ability to keep temperature the body temperature around respiration 37°C, is affected not only by air humidity temperature but also by infra-red meteorological variables like radiation air’s moisture content, wind clothing speed, and radiation levels airflow (Havenith 2005). Heat, which is produced as a result of metabolic activity plus external potential other heat gains (e.g., convection work through solar radiation), can be infra-red released through convection, radiation conduction conduction, respiration, radiation, and evaporation of 33 HEAT WAVE IMPACTS AND WARNING SYSTEMS RECENT HEAT WAVE EVENTS extreme heat (Zaninovic & of Cluj-Napoca in Romania in Matzarakis 2013). A proportion 2015 also shows economic European countries are of the deaths during heat waves losses related to heat waves. strongly affected by heat can be attributed to very ill The estimated potential loss waves (Figure 17; this natural people, who might have lived reached more than €2.5 hazard causes more deaths in longer without the heat stress million for each heat wave day, Europe than any other (Figure situation (Confaloniere et al. totaling more than €38 million 18). Recent examples of heat 2007). A study of three heat for the three cases considered waves include the record- wave events affecting the city in Cluj (Herbel et al. 2018). breaking heat wave in Europe in 2003 and the Russia heat wave in 2010, which caused unprecedented heat-related death tolls (Schär & Jendritzky 2004; Russo et al. 2015). The August 2003 heat wave caused more than 14,800 deaths in France, while Belgium, the Czech Republic, Germany, Italy, the Netherlands, Portugal, Spain, Switzerland, and the United Kingdom all reported high excess mortality rates (Confaloniere et al. 2007). In total, the 2003 heat wave caused more than 70 thousands deaths in Europe (Robine et al. 2008). European countries were also affected by heat waves during the summer of 2015 and 2019, when record maximum temperatures were recorded Figure 17. Annually averaged frequency of heat waves with durations of six days or greater exceeding the 90th percentile of daily maximum temperature in the (NOAA 2015; WMO 2019). months April through September, based on 1971–2000 E-OBS data. Southern and southeastern Source: E-OBS ECA&D (van Engelen et al. 2008). Europe was greatly affected by the heat wave of 2017 (Kew et al. 2018). Analysis of the impact of extreme thermal conditions on mortality in Croatia showed that mortality 77,637 13,818 during warm events is more FATALITIES CAUSED BY STORMS, FLOODS, pronounced than during cold FATALITIES CAUSED BY HEAT MASS MOVEMENTS, COLD WAVES, events (Zaninovic 2011). It was WAVE EVENTS DROUGHTS, FOREST FIRES, EARTHQUAKES, also shown that the prolonged VOLCANOES, TSUNAMIS effect of high temperatures can significantly increase Figure 18. Of all the natural hazards affecting the EEA member states mortality, which was the in the period 1980–2017, heat waves account for some 68 percent of the highest during the first three fatalities and about five percent of total economic losses. Source: EEA 2019. to five days of 34 HEAT WAVE IMPACTS AND WARNING SYSTEMS HEAT HEALTH WARNING SYSTEMS specific target groups (WMO & Casanueva et al. (2019) WHO 2015; Casanueva provides an overview of 16 Heat health warning systems et al. 2019). Ideally, a existing HHWSs in Europe. (HHWSs) and heat health combination of weather While before 2001 only one action plans (HHAPs) constitute elements related to the human operational HHWS was in place the means to address, manage, sensation of heat should be in Europe (in Lisbon), most and counteract the health- used as a risk indicator. European countries started to related risks of heat waves. Appropriate thresholds must be implement a HHWS after the HHWSs, which are often part of established for that combina- 2003 heat wave. The variables a wider HHAP, were developed tion, considering both daytime and thresholds used in Europe in many regions to better high and overnight low values, to issue warnings are very inform people about upcoming and being related to the diverse (Table 1). In most hot weather conditions and climatic variability common to countries, warnings are thus to reduce the negative the area. The effect of duration triggered based on maximum impacts of heat waves on should also be included. The or mean temperature only. human health. Guidance on thresholds may represent Some countries also consider how to develop HHWSs has absolute values (e.g., maximum minimum temperature when been issued jointly by the temperature exceeding 30°C) issuing a warning, and a few World Meteorological that are specific for a particular countries include other Organization and the World region. Alternatively, the climatic factors, like humidity. Health Organization (WMO & thresholds may be relative (e.g., Thresholds are often defined WHO 2015). A HHWS usually temperature exceeding the based on epidemiological comprises weather forecasts, a 98th percentile of the studies, where climatic method to assess the heat- maximum temperature) and variables are set in relation health relationship, the apply to all regions. The benefit to mortality (most countries) determination of threshold of this latter approach is that or to heat stress levels (e.g., values to issue warnings, a heat wave health assessments Austria, Germany); or they system of graded alerts, and would be similar across are based on climatological the communication of the alerts communities for relative extremes for the specific to the general public or temperature effects. region (e.g., high percentiles). Table 1. Heat warning system characteristics for different countries. PT: perceived temperature; Tmin, Tmax, Tmean: minimum, maximum, and mean temperature respectively. Source: Casanueva et al. 2019; DHMZ. Country Heat index Criteria for warning Target groups Hospitals and health resorts, childcare PT > 35°C for at least three days and Tmin ≥ 20°C Austria PT and Tmin facilities, mobile nursing services, (subject to modifications) medical and emergency organizations Yellow: Tmin > 20.2 or Tmax > 33.7 Croatia Orange: Tmin > 21.3 or Tmax > 35.1 Tmin and Tmax Public (Zagreb) Red: Tmin > 22.9 or Tmax > 37.1 If both conditions satisfied, higher category is applied. North Monthly thresholds for each of the four phases for 13 Retirement homes, general Tmax Macedonia cities in six regions from May to Sep. practitioners, workers Alert: Tmax: 35-38°C, Romania Tmax - Maximum response: Tmax: 35-40°C Yellow: Tmax > 31°C Public (genera), civil defense Slovenia Tmean and Tmax Orange: Tmax > 34°C and/or Tmean > 26°C in case of orange or Red: Tmax > 37°C and/or Tmean > 28°C red warning 35 HEAT WAVE IMPACTS AND WARNING SYSTEMS THE ROLE OF METEOROLOGICAL SERVICES Experience, historical Heat event National meteorological definition data services provide weather forecasts, usually monitor the country-specific risk indicators, and inform the public about the exceedance of threshold values. In some countries they Weather Warning are also mandated to provide heat wave advisories, while in forecast criteria other countries the local public Criteria health agencies are responsible fulfilled? for issuing warnings (WMO & WHO 2015). Thresholds to issue warnings NO YES are in most cases defined at country scale; however, some countries have defined region- specific thresholds (Casanueva EDUCATION AND INFORMATION et al. 2019). In many countries, WARNING heat health warning systems COMMUNICATION SEASONAL are established as part of the AWARENESS national heat health action plan (simplified example in Figure 19). At European scale, TARGET COMMUNICATION Specific Meteoalarm (Figure 20) is the interventions GROUPS official website providing alerts on extreme weather. It receives information from the national weather services. Figure 19. Simplified illustration on how to implement a HHWS as part of a wider HHAP (elements in the red box). Adapted from WMO & WHO 2015. HEAT HEALTH ACTION PLAN identification of vulnerable (like recommendations for Apart from alerting the public population groups (to make urban planners), and the when a heat wave is predicted sure that they are being definition of evaluation (through HHWSs), it is crucial to reached during an extreme procedures. In 2004, the inform people up front about event), the set-up of French authorities the devastating effects heat intervention plans and implemented local and can have on their health and communication strategies (to national action plans that about the appropriate ensure that warnings are included HHWSs, health and measures to take. Therefore, issued and communicated to environmental surveillance, raising awareness and the right people and that all reevaluation of the care of knowledge building in general involved partners and the elderly, and structural are important aspects of HHAPs organizations are informed and improvements to residential beyond warnings. HHAPs prepared), the determination institutions. Across Europe, usually also comprise the of medium- and long-term many other governments mitigation measures (local and national) 36 HEAT WAVE IMPACTS AND WARNING SYSTEMS The federal states inform predefined institutions and groups, such as hospitals, care homes, childcare institutions, care givers, and the Red Cross. Guidelines on how to behave during a heat wave are available on the website of the Ministry of Health. In case of extreme events, the Ministry of Health and the Austrian Agency for Health and Food Safety (AGES) jointly set up a phone hotline to provide advice for the general public. The positive effect of such awareness strategies is evident, as shown by a study by Fouillet et al. (2008). By modeling the expected number of heat wave deaths in the period 1975–2003 in France and extrapolating the expected number of deaths for the 2006 heat wave, the study showed that the actual excess mortality was markedly lower than that predicted by the model. This reduced death toll could be attributed Figure 20. Meteoalarm, which provides relevant information needed to prepare for in part to increased awareness extreme weather expected to occur in Europe, issued the highest grade (red) of the risk related to extreme warning for heat on August 4, 2017, for several countries, as displayed temperatures, preventive on the Meteoalarm website. Source: www.meteoalarm.eu. measures, and the set-up of the warning system. have implemented heat health national heat protection plan prevention plans (Casanueva specifies the warning Besides implementing and et al. 2019). In Croatia, one of procedure at national level, strengthening warning and the priority measures was the while at local level, HHAPs communication systems to implementation of the (such as the one for Vienna) prepare people for upcoming “Protocol on Treatment and define in more detail different heat waves and thus reduce Recommendations for actions that are to be taken health effects through raised Protection against Heat.” This before the warm season, awareness and better important protocol allows during the warm season, and preparedness, HHAPs can coordination of several during a heat event. As soon as and should also comprise national and city services, heat stress is predicted, ZAMG long-term strategies to with the DHMZ providing sends an alert to the Ministry alleviate the future impacts weather forecasts and of Health and other relevant of heat events. warnings. In Austria, the federal institutions. 37 7 CLIMATE ADAPTATION MEASURES Appropriate adaptation measures can reduce urban heat load and bring further benefits for the city. In light of climate change, both climate adaptation and climate mitigation strategies need to be included in urban action plans. Building on the information across the previous sections, this chapter introduces the concept of green, blue or white city agenda, along with examples from Graz and Klagenfurt am Wörthersee of how this can be applied in practice. CLIMATE ADAPTATION MEASURES “GREEN CITY” Vegetation, such as trees or parks, provide cooling through the effect of shading as well as evapotranspiration. Green roofs or vertical gardens, where a layer of vegetation grows on a rooftop or along a wall, also cool through this principle. Implementation: Parks, unsealing of soil, and creation of more permeable surfaces, green roofs, living walls, vertical gardens, green tracks, etc. Cooling through: Shading effect, evaporative cooling, insolation Co-benefits: Stormwater retention, energy savings, aesthetic value, recreation, biodiversity, ground water recharge, reduced subsidence “BLUE CITY” Water bodies such as ponds, lakes, or rivers can cool by evaporation, heat absorption, and heat transport. Water spray from fountains, for example, can locally have an even greater cooling effect because of the large contact surface between the water and air, stimulating cooling through evaporation. Implementation: Ponds, lakes, fountains, canals, re-naturalization, etc. Cooling through: Evaporative cooling, increased ventilation Co-benefits: Recreation, biodiversity “WHITE CITY” Causes of the UHI include high absorption of solar radiation as well as heat storage of paved surfaces or built-up areas. These can be counteracted by the use of „cool materials” that are generally lighter or reflect more solar radiation than traditional darker materials. Implementation: Bright (reflective) materials Cooling through: Reduced heat absorption through the reflection of solar radiation Co-benefit: Building energy savings, easy implementation 39 CLIMATE ADAPTATION MEASURES Buildings Sealed surfaces Low vegetation Water Unsealed surfaces Figure 21. Illustration of different climate adaptation measures. Increasing the fraction of vegetation in urban areas, implementing green or white roofs, and adding water bodies can reduce urban heat load, contribute to health and well-being, and bring further benefits for the city. Credit: ZAMG/Kainz and Hollósi. There are various options to on the climate conditions recreation. Green roofs can be counteract the UHI effect locally. In arid areas, measures used for urban gardening and through nature-based and requiring high water help maintain biodiversity in technological solutions consumption, such as intensive the urban area. Cool roofs, (Figure 21). These adaptation greening, may not be which reflect more solar measures broadly fall into sustainable. Moreover, the radiation than ordinary roofs, three categories, related to effectiveness in terms of UHI transfer less heat to the increasing the ratio of plants reduction depends strongly on building interior. In this way, and trees in a city (green city), the local climatological human comfort is increased by implementing the smart use of conditions and urban reducing indoor temperatures. water (blue city), and reducing geometry. Certain measures, In case air conditioning is the absorption of solar radiati- e.g., green roofs, can be installed, such roofs help save on by increasing its reflection applied only where the energy needed for cooling and (white city). “Cool” materials building construction allows it. increase energy efficiency. for roofs or pavements are Local wind circulation can Green roofs have a similar generally brighter, hence the enhance the propagation of insulation effect, while term “white city.” Such sur- cool air, however blocking of additionally supporting faces stay cooler in the sun airflow can also weaken the stormwater runoff and help reduce the UHI cooling effect. Therefore, management by soaking up effect, as less heat is careful planning of adaptation rain. These and other manifold transferred to the surrounding measures is needed to provide advantages of adaptation air (e.g., Akbari et al. 2001; the best solutions for cities. measures are often sufficient Santamouris 2014). The green to justify the initial costs and and water areas provide CO-BENEFITS technical difficulties in cooling through implementation. evapotranspiration, and trees’ Measures to counter the UHI shading effects also keep the effect are very often at the EVIDENCE-BASED surfaces cool (e.g., Gill et al. same time measures to ADAPTATION PLANNING 2007; Rizwan et al. 2008; improve the quality of life in Berardi et al. 2014). The cities. Parks, ponds, and Urban climate models can be success of these adaptation fountains provide room for used to quantify the effect of measures is clearly dependent different adaptation options 40 CLIMATE ADAPTATION MEASURES Example from Graz In the densely built Jakomini district in the center of Graz, Austria, urban climate model simulations were used to evaluate the potential for local cooling considering using different adaptation measures. The modeling simulations show that a strong cooling effect can be achieved by applying materials with high reflectivity on buildings’ walls and roofs, reducing area of sealed off surfaces (pavement), and increasing the number of trees on st_diff_016 streets and in open spaces (Figure 22). < -10 -10 - -9 -9 - -8 -8 - -7 -7 - -6 -6 - -5 -5 - -4 -4 - -3 -3 - -2 -2 - -1 -1 - 0 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9 - 10 Figure 22. Simulations of effectiveness of climate adaptation measures for the 287,995 128 km2 Jakomini district in Graz. The difference in mean annual number of summer days (2018) is shown in comparison to reference simulation in case of reduction of pavement by 50 percent (left), 30 thousands new trees of 10 m height on streets and 63.0 1.2 open spaces (center), and increase in roof albedo (0.7) (right). summer days tropical nights Adapted from Zuvela-Aloise et al. 2017. while considering local climate proportions of green and water Unsealing of paved areas is an conditions and urban areas. The major adaptation important adaptation structure. Using urban climate pathways in climate models are measure, not necessarily simulations, enables translated into modification in because of its direct cooling identification of critical zones land use and urban structure effect, but rather through in the city with increased characteristics, from which indirect effects of water environmental risks and in this alternative urban heat load retention in the soil. way support the prioritization simulations can be calculated Simulation of new green areas of adaptation plans. It is also and compared. The white city with urban climate models can possible to evaluate the scenarios consider enhanced help quantify the amount of effectiveness of urban sunlight reflectivity of sealed vegetation necessary to planning measures to reduce areas, i.e., roofs, walls, and provide a substantial cooling the heat load before the actual streets/sidewalks, which can effect for a specific area of the implementation. Examining be applied to individual city. The blue city scenarios, climate “what if” scenarios surfaces in different parts of where water areas are the with and without the the city. The green city focus of climate adaptation, implementation of adaption scenarios include various provide insight into how the measures can show the extent options for increasing cooling effect of water bodies, to which heat load is reduced vegetation, mainly the addition such as rivers, lakes, or ponds, by optimizing thermal of trees, bushes, or grass along can be enhanced through properties of buildings and streets and in open spaces, but spatial planning, e.g., by open spaces through increased also on building structures planning of free corridors for (either roofs or facades) 41 CLIMATE ADAPTATION MEASURES ventilation along the water environment for people living pathways (e.g., Theeuwes et in the area, interaction Example from Klagenfurt al. 2013). Recent studies have between planners and different shown that UHI mitigation stakeholders is necessary to measures should be applied ensure acceptance and extensively to have a sizable successful implementation in am Wörthersee effect over the city (Zuvela- compliance with building Aloise et al. 2016). However, regulations and guidelines. many adaptation measures Equally important is a good cannot be applied in the same communication process, way for each urban area. In where stakeholders and users some cases, instead of follo- can contribute to the wing one adaptation pathway, development of tailor-made a city can achieve the best applications. Practical solutions cooling performance with a that encourage engagement of combination of different different actors are more likely adaptation measures depen- to provide long-term benefits dent on the local urban than top-down approaches. characteristics. Although Analysis of adaptation adaptation pathways can be measures’ effectiveness can generalized in many ways, the include future climate project- final adaptation plans are city ions. Reference simulations for specific, and need to consider the most recent climate period many other aspects, including are compared with the future 100,851 120 km2 technical, institutional, RCP scenarios—e.g., RCP4.5 (2018) regulatory, social, environ- (peak of CO2 emissions in 2050) mental, financial, and many and RCP8.5 — until the end of 62.8 0.2 others, which go beyond the the 21st century with and summer days tropical n. scope of this report. With without adaptation measures. urban climate models, general The city of Klagenfurt am The results show that in case Wörthersee, located in Austria’s strategies can be designed into no climate change mitigation is southern Alps, is affected by climate tailored plans, then tested and achieved globally (RCP8.5), the change and increasing temperatures tuned in different stages of local climate adaptation in the urban area. In order to ensure implementation. In this way, measures are very likely not that its conditions remain livable in urban climate modeling can sufficient to compen-sate for the future for its citizens and help urban planners in the visitors, the city joined the New the large-scale warming trend. Covenant of Mayors in 2016 and is decision-making process of However, if CO2 emissions are taking actions to update the 2014 finding optimally cost- reduced suffici-ently (RCP4.5) Sustainable Energy Action Plan and effective, scientifically sound, and adaptation measures are revise it with climate adaptation and consistent solutions for implemented on a local scale, measures making it a Sustainable sustainable cities. A special an increase in heat load could Energy and Climate Action Plan. challenge in climate-resilient be largely mitigated by the Urban climate simulations have been performed to analyze the urban planning is to find middle of the 21st century future projections and possibilities appropriate adaptation (Oswald et al. 2020). This of climate adaptation in the city measures that provide a good finding emphasizes the fact considering two major adaptation cooling performance as well as that both climate adapta-tion pathways, white city and green city fit into the already existing measures and reduction of CO2 (Figure 23). cityscape. As these interven- emissions need to be consi- tions influence the social dered in urban action plans. 42 CLIMATE ADAPTATION MEASURES 1981–2010 (REFERENCE) 2021–2050 (RCP4.5 ) The white city scenario for HU_his_1981-2010 Hot days Klagenfurt am Wörthersee 0 considers a 20 percent increase 2 4 in sunlight reflectivity of roofs, 6 walls, streets, and sidewalks, 8 10 which could be achieved by 12 using reflective materials, e.g., 14 16 through white coating. The 18 green city scenario takes into 20 22 account the reduction of impervious surfaces by 30 percent, green roofs on 50 percent of suitable buildings, White city and an increase in the number of trees and vegetated areas. In addition, an afforestation area of 1.4 km2 is considered near the city. The results of the simulations show a substantial decrease in heat load. In the white city scenario, the mean annual number of hot days decreased by up to 20.7 percent; Green city for the green city scenario, the decrease was up to 20.2 percent (more trees) and up to 27.1 percent in case of afforestation near the city. An overall combination of adaptation measures (the combined white + city and green city pathways including the afforestation) adaptation Combined indicates an even stronger potential for the reduction of urban heat load. For this scenario, a decrease in average number of hot days of up to 44.0 percent is achieved. The daily Number of days temperature extremes are also -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 reduced, resulting in maximum air temperature decrease by Figure 23. Mean annual number of hot days is shown for the time period 1981–2010 1.7°C on a hot day. Climate (top left) and 2021–2050 (top right). The difference in the mean annual number of adaptation under future climate hot days for adaptation scenarios corresponding to white city, green city, and a is analyzed as well. If scenario combination of the two, with and without adaptation measures, is shown for the RCP4.5 is considered and no current climate period 1981–2010 and future climate scenario RCP4.5 for the time adaptation measures are period 2021–2050. Adapted from Oswald et al. 2020. implemented, the heat load would increase by the middle of year on average (white city) or8 future, an increase in hot days by the 21st century by an average hot days a year on average the middle of the 21st century of up to 10 days a year. The (green city). Moreover, if could be largely mitigated or adaption measures could reduce combined adaptation measures even reduced to lower levels this increase to six hot days a are implemented in the near than today. 43 R ROADMAP FOR INCREASED RESILIENCE TO URBAN HEAT ROADMAP FOR INCREASED RESILIENCE TO URBAN HEAT There are many steps that cities can take to make them more resilient to extreme heat events and the negative impacts of the UHI effect. The roadmap presented in this report represents a general disaster risk management approach that focuses on an improved understanding of risk, which can in turn inform specific plans and investments and guide implementation and evaluation of actions taken. Heat waves and UHI are often not the only hazards that cities face. This framework allows cities to consider multiple hazards that may be prevalent, such as floods, earthquakes, storms, etc. A number of these steps provide opportunities to integrate a risk management approach with urban planning and development. Risk-informed urban planning and development can help minimize climate change– related loss to public, private, and combined investments; it can also contribute to more sustainable development and planning, and, ultimately, more resilient economies and societies. The risk management approach reflected in the roadmap can also be applied to specific project investment processes or to specific hazards such as UHI effects. Cities need to gain a better understanding of what drives the heat waves and UHI effects they are subject to. They also need to understand the scope of their risk, including people and assets exposed and impacts of heat waves on specific areas or population groups, including the vulnerable or most at risk. Risk and impact information, together with information related to urban development (such as changes in the land cover, land use, or population growth) and climate change projections, forms the basis for identifying the most effective passive solutions, including green, blue, or white city measures. These measures should match local needs, preferences of stakeholders, and other considerations. The action plan for increased resilience to UHI effects should identify specific public investments and actions to promote green, blue, or white adaptation measures. These may include for example investments in open green spaces and public cooling areas; regulations for public and private investments, including green or reflective roofing, shading, or use of specific materials; subsidies for households, etc. An overall framework defining the goals, priorities, and specific implementation and coordination arrangements would underpin the action plan. The benefits of and considerations for specific measures are detailed in a number of reports (e.g., World Bank, forthcoming) and should be carefully assessed. There are analytics and models available to inform urban planning and infrastructure development resilient to future climate change. There is a range of tools and modeling techniques at different scales that can help compare potential benefits of specific measures and/or their combinations and thus inform decision making. The results can guide the subsequent development, implementation, and monitoring of an action plan with specific corrective or preventive actions and investments that address hazard risk and climate change. This report has used Urban Adaptation Support Tool (UAST) as presented in the Urban Adaptation to Climate Change in Europe report (EEA 2012). In 2011, the European Union published the “Non-paper Guidelines for Project Managers: Making Vulnerable Investments Climate Resilient” (EU–GL 2011). The methodology was updated within the EU-founded H2020 CLARITY project (https://clarity-h2020.eu, No. 730355) to comply with the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) and promote an integrated modeling approach for disaster risk reduction and climate change adaptation. In parallel to improved urban planning, cities also need to also plan for improved preparedness and response to UHI effects. As part of this effort, cities need to clearly define arrangements and investments for HHWSs and HHAPs to address, manage, and reduce the residual health-related risks to populations, including vulnerable groups. Better information about the exposed and vulnerable population and assets can improve the targeting of critical systems and plans to better meet emergency situations and people’s needs. 45 ROADMAP FOR INCREASED RESILIENCE TO URBAN HEAT - Definition of objectives Knowledge base - Understanding drivers and purposes - Inventory of existing knowledge and experience 3 Analyze Vulnerability 2 Evaluate Exposure - Analyzing to what extent a given exposed - Analyzing the distribution of elements at element at risk is damaged by a certain hazard risk considered (e.g., population, buildings, - Defining vulnerability classes (e.g., children/ infrastructure) in space and time adults/elderly) and functions for each element - Allocating all elements at risk in the area of at risk interst to vulnerability classes for each hazard type elements at RISK 4 Assess Risk and Impact Identify Adaptation Options 5 - Relating hazard intensities to exposure and - Selecting possible options vulnerability conditions in a given area - Assessing different adaptation options, including - Taking into account the magnitudes and their impact and effectiveness likelihoods of the impacts associated with the - Discussing with experts and stakeholders hazards - Considering numerical modeling procedures in order to include various scenarios in the analysis + with respect to the frequency of event occurrence and magnitude - Considering existing and future climatic risks and impact scenarios 8 Monitor and Evaluate 7 Implement Adaptation Action Plan - Consulting with stakeholders - Developing action plans for selected adaptation measures - Communicating results - Making decisions - Evaluating performance - Clarifying stakeholder roles and responsibilities - Monitoring changes in impact 46 ROADMAP FOR INCREASED RESILIENCE TO URBAN HEAT 1 Characterize Hazard - Identifying hazard conditions, relevant climate variables, and the combination of different parameters - Analyzing hazard based on its main characteristics under past and future climate conditions - Downscaling information in the area of interest expert HAZARD MAP group data requirements hazard indices appropriate spatial and tools and methods temporal horizons changes in land URBAN CLIMATE different scenarios, cover and land use, multi-model assessment, population growth DEVELOPMENT CHANGE downscaling expert group adaptation scenarios ADAPTATION e.g., white, green, and blue data MEASURES + requirements COST-BENEFIT ANALYSIS ACTION PLAN framework stakeholders concept 6 Appraise Adaptation Options - Undertaking an economic appraisal in form of a cost-benefit analysis of possible adaptation measures - Determining project limits, objectives and aims - Determining investment and operating costs - Assessing impact and effectiveness of options 47 R REFERENCES REFERENCES Akbari H., M. 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Images Cover page: ©ZAMG/Hollósi; p. 0/p. 1: © ZAMG/Hollósi; p. 2: ©ZAMG/Hollósi; p. 8 ©hans (roof-99895) – pixabay.com; p. 12 top ©goranh (evening- 3860435_1920) – pixabay.com; p. 12 bottom ©dimitrisvetsikas1969 (wawel-castle-4480556_1920) – pixabay.com; p. 14 ©free-photos (Hochhaus_symmetry) – pixabay.com; p. 18 ©Wien3420/Schedl; p. 21 ©ZAMG/Hollósi; p. 22 ©geralt (personal-3286017_1920) – pixabay.com; p. 24 ©ghitab27 (cluj-napoca- 3480861_1920) – pixabay.com; p. 25 ©ZAMG/Tordai; p. 26 ©ZAMG/Hollósi; p. 29 ©10314800 (linz-3743776_1920) – pixabay.com; p. 30 ©lefteye81 (tree- 3375139_1920) – pixabay.com; p. 36 ©ildigo (architecture-3344789) – pixabay.com; p. 39 ©lnlnln (architecture-3141107_1920) – pixabay.com; p. 40 ©Stadtpresse Klagenfurt/Helge Bauer-; p. 42 ©geralt (social-media-1635571_1920) – pixabay.com; p. 46 ©myrfa (files-1614223) – pixabay.com; p. 44/p. 45 ©ZAMG/ Hollósi. City statistics Population Mean annual number of summer days Vienna, Graz, Linz, Klagenfurt: (Tmax ≥ 25°C) between 1981 and 2010 https://www.statistik.at/web_de/statistiken/menschen_und_gesellschaft/bevoelker Vienna, Graz, Linz, Klagenfurt: ZAMG ung/ Cluj-Napoca: European Climate Assessment Cluj-Napoca: http://www.insse.ro/cms/files/Audit%20urban/Audit_urban_2018.pdf and Dataset, Squintu et al. 2019 Zagreb: https://www.dzs.hr/default_e.htm Zagreb: DHMZ Krakow: https://stat.gov.pl/en/topics/statistical-yearbooks/ Krakow: Bokwa et al. 2018 Area Vienna, Graz, Linz, Klagenfurt: http://www.gemeinden.at/gemeinden/ Mean annual number of tropical nights Zagreb: http://www1.zagreb.hr/zgstat/documents/Ljetopis%202007 (Tmin ≥ 20°C) between 1981 and 2010 /STATISTICKI%20LJETOPIS%202007.pdf same as above Krakow: https://www.krakow.pl/english/business/39148,artykul,krakow_in_numbers.html Cluj-Napoca: https://www.citypopulation.de/en/romania/cluj/_/054975__cluj_napoca/ 51 The International Bank for Reconstruction and Development / The World Bank 1818 H Street, N.W. Washington, D.C. 20433, U.S.A April 2020