POLICY BRIEF CLIMATE CHANGE, ENERGY AND ENVIRONMENT TURNING DOWN URBAN HEAT CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE Costas Cartalis September 2024 Cities are vulnerable to excessive heat associated with climate change because of their high population density, infrastructure and built-up areas. Appropriate measures to mitigate urban heat need to consider the‘vibe’ of the city, as well as its urban functions, urban form and urban fabric. Households with lower incomes are more exposed to heat, mainly because of the moderate or poor quality and age of the buildings they tend to occupy and the higher density of heat sources in their vicinity. It is therefore necessary to prioritise the application of urban heat mitigation plans in these areas. Involving local communities in the urban heat mitigation process is essential to raise awareness of climate change and to encourage local initiatives to increase equitable resilience.

CLIMATE CHANGE, ENERGY AND ENVIRONMENT TURNING DOWN URBAN HEAT CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE Contents INTRODUCTION ............................................... 2 ‘LISTEN’ TO THE CITY ......................................... 3 HEAT IS NOT EVENLY DISTRIBUTED ....................... 3 URBAN MORPHOLOGY MATTERS .......................... 4 A NEW LOOK AT THE URBAN FABRIC ..................... 4 GREENERY BY ALL MEANS .................................. 5 BLUE URBANISM .............................................. 7 NEIGHBOURHOODS IN THE SPOTLIGHT .................. 7 HOW TO DRAW A HEAT ROAD MAP FOR URBAN CLIMATE RESILIENCE ......................... 7 TAKEAWAY MESSAGES ...................................... 7 References ......................................................... 8 About the author ................................................... 9 1

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE TURNING DOWN URBAN HEAT CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE INTRODUCTION Cities are vulnerable to excessive heat associated with climate change because of their high population density, infrastructure and built-up areas. In particular, the relationship between cities and climate change is multi-fold: – An urban area is affected by climate change as a result of higher temperatures, longer periods of high temperatures and the increasing intensity, duration and frequency of heatwaves. – Rising air temperatures as a result of climate change are added to the‘urban heat island’(UHI) phenomenon (Figure 1), namely the urban influence on local microclimates: urban areas are warmer than the surrounding rural areas because of the lower vegetation cover, stronger absorption of solar radiation – due to the geometric structure of the city and the properties of surface materials – and anthropogenic heat sources, such as buildings, industrial activities and vehicular traffic. Overall, the UHI effect is generally stronger at night, as it is shaped largely by the slower cooling rate of urban areas compared with rural ones. On the other hand, the greatest heat burden and higher energy consumption in buildings for the purpose of cooling occur during midday hours. – The development of a city modifies land use and land cover, and consequently affects heat flows and evaporation rates, as well the spatial distribution and intensity of anthropogenic heat sources. – The specific morphology of an urban area significantly affects ventilation mechanisms and therefore may either exacerbate or mitigate surface(air and land) temperature conditions. Excessive urban heat has a negative impact on human health, especially for vulnerable groups. It also increases energy use for cooling, leads to poor city thermal comfort, 1 intensifies energy poverty, deteriorates air quality and results in socio-economic problems. For example, in Athens the added urban heat increases buildings’ energy consumption by 4.1 per cent for each degree increase in air temperature. Additionally, a comparative study of data on daily mortality from cardiovascular and respiratory causes in Athens(Paravantis et al., 2017) concluded that the mortality of people over 65 increases dramatically. Finally, the higher temperatures prevailing in a city tend to increase the concentrations of photochemical pollutants, which exacerbate respiratory diseases. Figure 1 The Urban Heat Island Late afternoon temperature °C Rural Suburban Residential Commercial City Urban Residential Park Source: World Meteorological Organization WMO, https://community.wmo.int/en/activity-areas/urban/urban-heat-island Suburban Residential Rural Farmland 1 Thermal comfort is a state of mind that reflects a person’s satisfaction with the thermal environment. Thermal comfort can also be defined as a person’s awareness of air temperature and heat(https://www.sciencedirect.com/topics/earth-and-planetary-sciences/thermal-comfort) 2

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE ‘LISTEN’ TO THE CITY Selecting appropriate measures for urban heat mitigation requires a prior understanding of a city in terms of its‘vibe’, urban functions, urban form and urban fabric. 2 It also requires an analysis of the temperature field up to the present(Figure 2) and the heat mapping of the city under consideration (mainly in urban units and at high spatial resolution at the block level). Other essential factors include the temporal (intra-day, seasonal) and per area heat risk, 3 the detailed definition of urban climate zones, and estimates of the air temperature, as well as the frequency and intensity of heatwaves in subsequent climatic periods. Only with knowledge of all of the above it is possible to develop specialised urban heat mitigation plans per urban climate zone, maximise the intervention results and avoid projects of limited or almost zero impact. Figure 2 Mean annual temperature, trends and anomalies for Athens, Greece. 20 20 Mean yearly temperature, trend and anomaly,1979-2023. Mean yearly temperature, trend and anomaly, 1979-2023. Athens 37.38°N, 23.73°E. Athens 37.98°N, 23.73°E. 19 19 mean (°C) mean (°C) 18 18 17 17 16 16 anomaly stripes anomaly stripes 197 19 98 10 98 11 98 12 98 13 98 14 98 15 98 16 98 17 98 18 98 19 99 10 99 11 99 12 99 13 99 14 99 15 99 16 99 17 99 18 99 29 00 20 00 21 00 22 00 23 00 24 00 25 00 26 00 27 00 28 00 29 01 20 01 21 01 22 01 23 01 24 01 25 01 26 01 27 01 28 01 29 02 20 02 21 02 22 023 Year Source: https://www.meteoblue.com/en/climate-change/athens_greece_264371 meteoblue.com HEAT IS NOT EVENLY DISTRIBUTED Variations in the intensity of anthropogenic heat sources within the urban fabric, combined with urban morphology and increasing temperatures because of climate change, determine people’s urban heat exposure. In Figure 3, urban heat exposure(vertical axis, Urban Heat Exposure Index – UHeatEx) is presented alongside household incomes in the wider urban area of Athens. Households with lower incomes experience greater heat exposure mainly because of the moderate or poor quality and the age of the buildings they tend to inhabit, the higher density of heat sources in their vicinity(for example, major roads, industrial units, high building density), and/or the lack of green spaces. Figure 3 The relationship between household income and the Urban Heat Exposure Index –(UheatEx) for Athens 8 6 UHeatEx 4 2 0 10,000 50,000 100,000 Household income, logscale[€] Source: Agathangelidis, I., Cartalis, C., Santamouris, M.(2019): Integrating Urban Form, Function, and Energy Fluxes in a Heat Exposure Indicator in View of Intra-Urban Heat Island Assessment and Climate Change Adaptation, in: Climate 2019, 6(7), 75. https://doi.org/10.3390/cli7060075, figure 13. 2 The materials found in an urban area, such as cement, asphalt and greenery. 3 Heat risk refers to the potential for adverse health effects due to exposure to high temperatures. This risk is particularly significant during heatwaves. 3

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE Figure 4 presents the distribution of the Urban Heat Exposure URBAN MORPHOLOGY MATTERS Index for the wider urban area of Athens for 2019(higher Urban morphology significantly affects, especially in city values in red). streets, land surface temperature and consequently, because of heat transfer, air temperatures close to the surface. Specifim e a 2 t 0 e 1 2 9 0 , 1 7 9 , , 7 7 5 , 75 Figure 4 Distribution of the Urban Heat Exposure Index(UHeatEx) for the wider urban agglomeration of Athens for 2019 cally, the higher t 1 h 8 e o 1 r f 8 a 2 t o i 8 o f 2 o 8 f building height to street width, the higher the air temperature at the surface level, especially at night time, because of the increased trapping of both the reflect 1 e 8 d o 1 s f 8 o 2 l o a 8 f r 2 r 8 adiation and the thermal radiation emitted by the ground, as well as the reduced wind speed at the ground level. This negative impact becomes more pronounced during heatwaves and results in the retention of heat in the built environment. In streets with these characteristics, it is necessary to reduce land surface temperatures, for example, by increasing greenery, using cool materials at the surface and at the top of buildings, and removing heat sources such as vehicular traffic and converting them into pedestrian or low-traffic streets. In Figure 5, the distribution of streets in the centre of Athens is colour-coded according to the height-to-width ratio(aspect ratio, H/W). Streets marked in orange and red are the highest priority for conversion, provided a comprehensive traffic study is conducted prior to any technical interventions. Fig F u ig re ur 1 e 2. 12 S . p S a p t a ia ti l al d d is i t s r t i r b ib u u ti t o io n n o o f f t t h h e e U U H H e e a a t t E E x x i i n nd d i i c c a a t t o o r r f f o o r r A A t t h h e e n n s s a a t t 1 1 0 0 0 0 -m -m et e e t r er re r s e o s l o u l t u io t n io ; n s ; ca s l c e ale Source: Agathangelidis, I., Cartalis, C., Santamouris, M.(2019): Integrating Urban Form, var v y a i r n y g in f g ro f m rom low low (0 Fu ( ) n 0 c t ) t o io t n o h , a i h n g d i h g En h ( er 1 g ( 0 y 1 F ) 0 lu ) t x h e t s h e in e rm r a m H a ea a l t l e E e x n p n o v s v u i i r r e r o o In n n d m ic m at e o e r n n in t t a Vi l ew q o u f a a In l l t i r i a t t y y U . rban Heat Island Assessment and Climate Change Adaptation, in: Climate 2019, 6(7), 75. https://doi.org/10.3390/cli7060075, figure 12. A NEW LOOK AT THE URBAN FABRIC p T S a h p t T a e ia t h i a l a e v l d a e d i v s r i t s a e r t r g i r b a i e b u g u m t e i t o i m i o n n n i i n o m o f i f m u t t h m u h e e m U T U T α H H α ( e e T ( a a T t α t E E α m m x x in in i i ) ) n n d d d d i u u i c c r a r a i i t t n n o o r g g r f f t t o o h h r r e e A A w w t t h a h a e r e r n m n m s s a p p a t e t e 1 r 1 r 0 io i 0 0 o d 0 -m d -m ( e M ( t M e e t a r e a y r r y – e r S – s e o e S s l p o e u t p l t u e i t o m t e n io T m b ; h n e s b e ; c r e a ) s in l r c f e c ) a o r l f r e e o a t r s h e t e d h y e a e b y a s e r o s a rp r 2 s t 0 io 1 2 n 3 01 o 3 f solar radiation by urban structures 1 2 m l 8 0 o 1 w l w o 8 w ( a w 0 s ( ) 0 a t c ) s o a t c o l h c a i h u g lc i h l g u a T h ( l t h 1 a e ( 0 e t 1 d e ) 0 d s ) t f p h o t f h a e r o e r t r i m fi r a m f l v a i a v e l d l e e is w e n t n w r v e i v b i e a i r u r a o t o t h n i n h o e m m e n r r e e s n o n s t t t f a t a a t l t i h i o q o e u n n a a s U l l i i i r t t n b y y. a t n h e H c e e a n n t t t r E r a x a l p l n o n e s e u ig i r g e h h b I b n o o d rh r e h x o o d od s c s on f o t A f rib A th u t e t h e n e s s n s ( i s g si n ( t s i e f i i s t c e a 0 s n 7 t – 0 ly 1 7 1 – to 11 the degradation of the urban therg F u ig r u e r 8 e ). 8 A ). l A l l t l h t h e h ig e s h t s a li t g t a i h t o i t n o s n t s h i s e t i e t u e s n s c e c o v o e r r n r r e e d s s i p s p t o r o i n b n d uti t o o n t o h f e h L L e C a C t Z Z in 2 2 th c c e l l a a c s s i s t s y ( , b ( a b o o f t a h t c h t at a o t 10 1 0 0 0 m m -m a a l e n a n d n vi d a ro t a n 4 t m 0 4 0 e 0 n m 0 t. -m U sc s a in s l c g e a ) n ; le at ) u ; ral or artificial materials with high g m e m in i i n m im um um T T α α ( T (T α α m m in in ) ) d d u ur r i i n n g g t t h h e e w w a a r r m m p p e e r r io io d d (M (M a a y y –S – e S p e t p e t m em be b r e ) r f ) o f r o t r h t e h y e e y a e rs ar 2 s 01 2 3 013 w v ev r, e t r h , e th y e d y i d ff i e b ff r e e i r c n o in n th s t i e h d e e d r d e e d r e i r v f i o v e r e d j d u U s U t H H re e s e a i a li t e t E E n x x ce s . c I o n r p e a s. r . t T i T c α u α m l m i a n i r n , w t w h as e a s h e i s g le h c l e e t s e c t d t v e a t d o lt b o e b e r e x f a l e e m x c a t i i n m v e it i d y n , e o a d f s , s U o a l H s ar U I U r H C a L d I i i U a s t C io L n on building facades, roofs and u c l u a l t a e t d ed fo f r or fi f v iv e u e w e w s e o e a f a t t h t h h e e e r r in s s d t t a e a t x t i i o a o r n n e s fo in un th d e in c t e h n n e t t r c r a e a l n l n t n r e e e i o g ig f h h A b b t o h o r e h r n h o s o a d o n d s d s o P f o ir A f ae A t u h t s e h , n e s n ( s s s i i d ( t s e e i s w te 0 a s 7 lk – 0 s 1 7 i 1 – n 1 u 1 rban areas as an adaptation measure modifies e d d o o m mi i n n a a n n t t l l y y a a n n o o c c t t u u r r n n a a l l p p h h e e n n o o m m e e n n o o n n [4 [ 3 4 , 3 1 , 3 1 1 3 ] 1 d ] u d e ue to to sl s o l w ow er e c r o c o o l o in li g ng ra r te a s te f s or fo t r h t e h d e e d n e s n er se u r r u ba rb n an l t l h t e he st s a t t a i t o i n on si s t w i e te s h s e c r c o e o r t r r h r e e e s s p d p r o o iv n n in d g t f o or t c h e e s o L L f C C e Z x Z ce 2 2 ss c c i l v l a e a s s u s s r ( b b ( a b o n o th h th e a a t a ti t 1 n 0 1 g 0 0 r 0 e m a -m c a h n a h d n ig d a h t a 4 t 0 4 r 0 a 0 d m 0 ia -m t s i c o a n s l c e b a ) a ; l l e a ) n ; ce and air temperature in the city. A highly rea S s. inc S e in l c o e ng l o te n r g m -te c r a m nop ca y n l o a p y y er t l e a m ye p r er t a e t m u p re e s ra fo tu r r t e h s e s fo tu r dy th a e re s a tu w d e y re a n r o e t a av w a e il r a e ble n , o m t e a a v s a u i r l e a m ble e , nts d ff i e ff r e i r n in th t e he d d er e v i r a v i l v u e e e d d s. U U H H i H g e h e a a v t t E a E l x u x e s s co ar r e es a . . ls T T o α α m o m in b in s w e w a rv s a e s d e s l in ec l t e t h e c e d te w t d o e t s b o t e e b r e n e xa p e m a x r a i t n m o e f i d n , e a d s fl , e U a c H s tiv U I e U H C s L u I r i U f s a C c L e absorbs less solar radiation, resulting in a lower e a R su S r L em w e e n r t e s u in se t d he (S R e S c L tio w n er 2 e .3 u ) s , e c d or ( r S e e s c p ti o o n n d 2 i . n 3 g ), t c o or a re c s o p m on b d in in e g d t e o ff a ec c t o o m f b m in i e c d ro e s f c f a ec le t o a f n m d i l c o r c o a s l c a s l c e ale y a a n n o o c c t t u u r r n n a a l l p p t h h h e e e n n u o r o m b m a e n e n n a o g o n g n [ lo 4 [ m 3 4 , 3 1 e , 3 r 1 a 1 3 t ] i 1 o d ] n u d o e u f e t A o t h o s e l s o n l w s o . w er e c r o c o o l o in li g ng ra r te a s te f s or fo t r h t e h d e e d n su e s r n e f r s a e c u e r r u b te a r m b n a p n erature and, because of reduced heat transfer, d ss lo es ca [ l8 s 9 c ] a . le T p h r e oc r e e s s s u e l s ts [8 p 9] r . e T se h n e t r e e d su i l n ts T p a r b es le en 6 ted in i d n ic T a a t b e le th 6 a i t nd U ic H at e e a t t h E a x t U va H lu ea e t s Ex fo v ll a o lu w es th fo e llo T w α min o te n r g m -te c r a m nop ca y n l o a p y y er t l e a m ye p r er t a e t m u p re e s ra fo tu r r t e h s e s fo tu r dy th a e re s a tu w d e y re a n r o e t a av w a e il r a e ble n , o m t e a a v s a u i r l e a m ble e , nts u T re α m m in e m nt e s a w su e r l e l m , r e F e i n g fl u t e s re c w t 5 in el g l, b r o ef t l h ec t t h in e g st b o o r t e h d t w he a s r t m or t e h d d w ur a i r n m g th th d e u d r a in y g a t n h d e t d h a e y s a u n b d se th q e ue s n u t bs n e i q g u h e tt n i t me u in se t d he (S R e S c L tio w n er 2 e .3 u ) s , e c d or ( r S e e s c p ti o o n n d 2 i . n 3 g ), t c o or a re c s o p m on b d in in e g d t e o ff a ec c t o o m f b m in i e c d ro e s f c f a ec le t o a f n m d i l c o r c o a s l c a s l c e ale g s h e. tt E im sp e e r c e ia le l a ly se f . o E r D s t p h is e e tr c n i i b a o u l r t l t i y o h n f e o r o r n f t s s h t t r e a ee t n i t o o s n r in th ( t S e h i r e t n e ce 1 s n t 1 a t ) r t , e i t o o h n f e A ( h S th i i g t e e n h s 1 e 1 a r c ) a , c m o th rd o e i u n h g n ig t to h o t f e h r g e r a h e m e e i n o g u h s t n p -t t a o o c -w e f g i a d n r t e h d e r n t a h t s i e o p , a a t s c e s e r o m a c e n i d a d t t e h d e aspect ratio. T p h r e oc r e e s s s u e l s ts [8 p 9] r . e T se h n e t r e e d su i l n ts T p a r b es le en 6 ted in i d n ic T a a t b e le th 6 a i t nd U ic H at e e a t t h E a x t U va H lu ea e t s Ex fo v ll a o lu w es th fo e llo T w α min u n r g aesm e s ff oe e cn c ita t s s tew l d e e d lclo t , o orel s if i nl g eg n ct i ei fi nf c fge a c n bt t so l t y lhe l d o th w teo e s r tso t ig e re m ndif p iwc e a r a a nr t tm u ly r th e l s od ; w w uer h irn il tg e emt i h t pe b e e dr l aa o ty n u g ar i en n sd g ; t t h o we t hs h iu e leb m siet o q r bu p ee h lno o tn l g o i g n i g ca t l o ty t p h e e of o e rp ll h , o re lo fl g e i c c t a in l t g yp b e ot o h f t d h e e ns s e to ly re b d ui w lt a L r C m Z th s. during the day and the subsequent nighttime ey s l e yf . ob E ru s t p hil e et c Ln ia oC l r l Zt y hs f e. o r r n t s h t e at n io o n rth (S e i r t n e 1 st 1 a ) t , i t o h n e ( h S i i g te h 1 e 1 r ) a , m th o e u h n ig t h of er gr a e m en ou s n p t a o ce f g an re d en th s e p a a s c s e o a c n ia d ted d co t T o o a l s b i i n l g e g n 6 i e . fi f C c fe o a c m n t t s p ly a l r e i l d s o o w n to e o r f s t ig h e e m ni a f p v ic e a r a a n g t t u e ly r m e l s i o n ; w i w m e h u r m il t e e a m i i t r p b te e e m r l a o p t n u e g r r a i e t n s u g ; re to ( w T t α h h m i i e l n e ) m a i t t o f r b iv p e e h lo c o n o l m g o i g p n i a g c c a t t l m o ty i t d p h e r e is o e f (LCZ T t a y b p l e e o 6. f C d o en m s p e a ly ris b o u n il o t f L th C e Z a s v . erage minimum air temperature( T α min ) at five compact mid-rise(LCZ 2) Zs 2 . ) sites in Athens, for 2013–2018(May–September). Site ID refers to site codes of Figure 8. sites in Athens, for 2013–2018(May–September). Site ID refers to site codes of Figure 8. mparison N o a f m th e e averag S e i m te in ID imum a L i o r c te a m tio p n era (W tur , e N ( ) T α min ) E a l t e f v iv a e ti c o o n m ( p m ac ) t m U id H -r e is a e tE (L x CZ T α min (°C) par N iso am n o e f the avera S g i e te m I i D nimum air L te o m ca p t e io ra n tu (W re ,N ( T ) α min ) at fi E v le e v c a o t m io p n a ( c m t m ) id-r U ise H ( e L a C tE Z x 2) T α min ( ◦ C) thens N , f e o o r s 2 K 01 o 3 s – m 20 o 1 s 8(May 0 – 7 Septem 2 b 3 e ° r 4 ) 3 . ′ S 5 i 7 te ′′, ID 37 r ° e 5 f 7 er ′ 3 s 2 t ′ o ′ site code 8 s 5 of Figure 8. 6.3 23.2 s, for 2013–2018(May–September). ◦ Site ID refe ◦ rs to site codes of Figure 8. Neos A Ko m sm pe o l s okipoi 07 08 2 2 3 3 °4 4 5 3 ′ 3 5 0 7 ′′ ” , , 3 3 7 7 °5 5 8 7 ′ 5 3 4 2 ′′ ” 136 85 5.5 6.3 22.5 23.2 m A e mpeloki S p i o te i ID L 0 o 8 cation(W 23 ,N ◦ 4 ) 5 30” E , 3 le 7 v ◦ 5 a 8 tio 54 n ” (m) UHe 1 a 36 tEx T α min (°C 5. ) 5 ◦ 22.5 N S e it a e S ID myrni Lo 0 c 9 ation( 2 W 3 , ° N ◦ 43 ) ′ 10 ′′, 37 E ° ◦ l 5 e 7 v ′ 5 a ′ t ′ ion(m) 51 UHeatEx 4. T 0 α min ( C) 23.0 o N sm ea o S s myrni 07 23 0 °4 9 3 ′ 57 ′′, 37° 2 5 3 7 ′ 3 4 2 3 ′′ 10”, 37 5 8 7 5 5” 6 5 .3 1 23.2 4.0 23.0 Patissia ◦ 10 2 ◦ 3° ◦ 43 ′ 47 ′′, 38° ◦ 1 ′ 19 ′′ 90 3.4 22.3 oki P p a o t i issia07 08 2 2 3 3 ° 1 4 04 5 3 ′ 3 5 0 7 ′′ ” , , 3 3 7 7 ° 2 5 53 8 7 ′ 5 43 4 32 ′′ ”47”, 38 1 13 1 6 98”5 5 9 .5 0 6.3 22.5 32.43.2 22.3 my M rn ar i ou M s0s a 8i ro0u9ssi 2 2 3 31 ° ◦ 1 4 4 31 5 ′ 11 3 0 0 ′ ” ′, , 3 3 7 7 2 ◦ ° 2 35 53 ° 8 7 ◦ 4 ′ 4 5 5 8 8 ′ 4 ′′ 3 ”3 6 6 ′′ ” , , 3 3 8 8 ° ◦ 2 2 ′ 55 5 14 41 ′′ ”36 2345 2 . 3 0 55.5 2.6 23.0 22.62.5 20.9 20.9 09 23 ◦ 43 10”, 37 ◦ 57 5” 51 4.0 23.0 sia 10 23° ◦ 43 ′ 47 ′′, 38° ◦ 1 ′ 19 ′′ 90 3.4 22.3 UHeat 1 E 0 x demons 2 tr 3 at 4 e 3 s 4 t 7 h ” a , t 3 t 8 he 1 u 19 rb ” an thermal 9 l 0 andscape of A 3. t 4 hens is cha 2 r 2 a .3 cterized by a high a U utsi H asli ea v t a E ri x 1 a 1 b d i1 e l1i m ty o , n b s o t t2 r 2 h3 a 3 ° t ◦ a4 e 4 m8 s 8 ′ 3o t 3 h 6n 6 ′ a g ′ ” , t , 3d 3 t 8 h 8 i°f ◦ e 2f 2 e ′ u 5r 5 4e r 4 n ′ b ′ ” t an di t s h tr e i r c m t2s3 a 5a 2 l n 3 l 5 d an f d o s r c n a e p a e 2r.b o 6y f 2 A u .6 r t b h a e n ns 2b0 i l s o.9c c k h 2 s a 0 . . r 9 A ac t t f e i ri s z t e s d ig b h y t, a th h is igh a r l m var l i i a n b e i q li u ty it , y bo s t e h em am s o to ng be di a ff s e so re c n ia t t d ed ist w ri i c t t h s t a h n e d s f o o c r io n e e c a o r n b o y m u i r c ba st n a b tu lo s c o k f s. re A si t d fi e r n s t t s s . i L g o h w t, t U hi H s e th a e tE rm x al demonstrates that the urban thermal landscape of Athens is characterized by a high u u it e y s s a e r em fo s u t n o d b i e n a th ss e o a c f i f a lu te e d nt w n i o t r h th th a e nd so s c o i u o t e h c e o a n s o te m rn ic a s r t e a a t s u a s n o d f h re ig s h id v e a n l t u s e . s L a o r w e fo U u H nd ea i t n E t x he va lo lu w e e s rare e i m ty o , n b s o t t r h at a e m s o th n a g t d th if e fe u re r n b t an di t s h tr e i r c m ts a a l n l d an f d o s r c n a e p a e rb o y f A ur t b h a e n ns b i l s oc c k h s a . r A ac t t f e i ri s z t e s d ig b h y t, a th h is igh d om in e t a h n e d a m ffl e u d e iu n m t n -i o n r c t o h m a e n w d e s s o t u an th d e c a e s n te tr r a n l a a r r e e a a s s . A an m d o h r i e g c h le v a a r l v u ie e w s a c r a e n f b o e u o n b d ta i i n ne t d he by lo e w xa e m r-i n n i c n o g me t , y bo s t e h em am s o to ng be di a ff s e so re c n ia t t d ed ist w ri i c t t h s t a h n e d s f o o c r io n e e c a o r n b o y m u i r c ba st n a b tu lo s c o k f s. re A si t d fi e r n s t t s s . i L g o h w t, t U hi H s e th a e tE rm x al m r e e d la i t u io m n s i h n i c p o b m e e tw w e e en st t a h n e d m c e e a n n tr h a o l u a s r e e h a o s l . d A in m co o m r e e p cl e e r a p r o v s i t e a w l co c d an e f b o e r o ye b a ta r i 2 n 0 e 1 d 1 b (G y r e e x ek am M i i n n i i n st g ry the o d b i e n a th ss e o a c f i f a lu te e d nt w n i o t r h th th a e nd so s c o i u o t e h c e o a n s o te m rn ic a s r t e a a t s u a s n o d f h re ig s h id v e a n l t u s e . s L a o r w e fo U u H nd ea i t n E t x he va lo lu w e e s rare o F n in sh an ip ce b ; et h w tt e p e :/ n /w th w e w m .g e s a is n .g h r o /g u s s is e / h in o f l o d /g in si c s o _s m it e e/ p P e u r bl p ic o I s s t s a u l e c /) od a e n f d or t y h e e ar co 2 r 0 r 1 e 1 sp ( o G n r d e i e n k g M a i v n e i r s a tr g y e of u d e iu n m t n -i o n r c t o h m a e n w d e s s o t u an th d e c a e s n te tr r a n l a a r r e e a a s s . A an m d o h r i e g c h le v a a r l v u ie e w s a c r a e n f b o e u o n b d ta i i n ne t d he by lo e w xa e m r-i n n i c n o g me H nc e e a ; tE h x ttp va :/ l / u w e w s( w n . o g n s i r s e .g si r d / g en si t s ia / i l n l f a o n / d gs u is se _s z i o te n / e P s u w bl e i r c e Is e s x u c e lu /) d a e n d d fr t o h m e c c o o r n r s e i s d p e o ra n t d io in n g ). F av ro e m rag F e ig U ur H e e 1 a 3 t , Ex p o b m e e tw w e e en st t a h n e d m c e e a n n tr h a o l u a s r e e h a o s l . d A in m co o m r e e p cl e e r a p r o v s i t e a w l co c d an e f b o e r o ye b a ta r i 2 n 0 e 1 d 1 b (G y r e e x ek am M i i n n i i n s 2 t g ry the o s l ( l n ow on s -r t e h s a i t d a en c t o i r a r l e l l a a n ti d on us is e p zo re n s e e s n w t b e e r t e w e e x e c n lu h d o e u d se fr h o o m ld c i o n n co si m de e r a a n ti d on U ). H F e r a o t m Ex F ( i R gu = re 0 1 .4 3 5 , ) i , t a f l o b l e lo it ws w tt e p e :/ n /w th w e w m .g e s a is n .g h r o /g u s s is e / h in o f l o d /g in si c s o _s m it e e/ p P e u r bl p ic o I s s t s a u l e c /) od a e n f d or t y h e e ar co 2 r 0 r 1 e 1 sp ( o G n r d e i e n k g M a i v n e i r s a tr g y e of o a d c e o r r a r t e e l i a n ti s o t n ren is g p th r ; e a se s n ig t n b if e i t c w an e t e s n pr h e o a u d s o e f h t o h l e d in in d c ic o a m to e r a v n al d ue U s H is e f a o t u E n x d ( f R o 2 r m = e 0 d .4 iu 5 m ), a in lb c e o i m t e m s, o w de it r h ate w s( w n . o g n s i r s e .g si r d / g en si t s ia / i l n l f a o n / d gs u is se _s z i o te n / e P s u w bl e i r c e Is e s x u c e lu /) d a e n d d fr t o h m e c c o o r n r s e i s d p e o ra n t d io in n g ). F av ro e m rag F e ig U ur H e e 1 a 3 t , Ex gher UHeatEx for the areas of central Athens. e a n c g o t r h r ; el a at s io ig n n i i s fic p S a o r u n e rc s t e e : s R n e p m t r o b e te e a Se t d n w sin o e g f e U n n t it h , h D e e o p i a u n rt s m d e en i h t c o o a f l t E d n o vi r r i o n n v m c a e o n l m t u al P e e h s ys a ic i n s s , d N f a o t U io u n H a n l a d e nd a K f t a E o po r x di m s ( tr R ia e n 2 d U = n i i u ve 0 r m s . i 4 ty 5 o i ) f n , At c a h o e l n b m s ei e t s, with higher dential land use zones were excluded from consideration). From Figure 13, it follows na e t n Eis g xp th fro ; er a ste s hn ig et n ab i r f ee i t c aw a s n eo t ef s n p ce r h e no a tu d ras o le f hA t o h thl e de i n n ins d .c ic o a m to e r a v n al d ue U s H is e f a o t u E n x d ( f R o 2 r m = e 0 d .4 iu 5 m ), a in lb c e o i m t e m s, o w de it r h ate C x l f i o m r a t t h e e c a h r a e n as ge of is ce e n x t p r e a c l t A ed th t e o ns a . ugment the impacts of the current urba 4 n overheating. As follows nificant spread of the indicator v ◦ alues is found for medium incomes, with higher ◦ Figure 14, a positive trend of 0.24 C per decade for the annual mean temperature and of 0.28 C areas of central Athens.

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE also leads to a lower air temperature. Thus, one adaptation measure is the use of cool materials that can be applied to building envelopes, as well as other surfaces in the urban built environment, such as parking lots, sidewalks and building exteriors to reduce temperatures on these surfaces. In a simulation study in the Athens area during the summer period, it was found that increasing the reflectivity of the city’s surface by 40 per cent results in a reduction of air temperature at 2 metres above the ground surface by as much as 1.5°C. GREENERY BY ALL MEANS The use of greenery can significantly reduce heat in open spaces, as through reflection and absorption, trees can remove a large amount of incoming solar radiation. Practically, vegetation in open urban spaces offers shade and lower temperatures under the tree canopy compared with the surrounding area. Shaded surfaces, for example, can be 11–25°C cooler than the maximum land surface temperatures of non-shaded materials. Another way vegetation can contribute to temperature reduction is through evapotranspiration, as the conversion of water from liquid to gas(water vapour) by vegetation lowers the temperature of both the foliage and the air. Evapotranspiration in combination with shading can help reduce peak summer air temperatures by 1–5°C. At the same time, the use of vegetation on roofs(green roofs) can also lead to a reduction in air temperature. Results show that the overall heat flow entering a building under a green roof is lower than in the case of a conventional concrete roof without greenery, regardless of weather conditions. An interesting research finding is that medium-sized parks can cool neighbouring areas with about the same intensity as larger parks. Figure 6 shows the correlation between the cooling effect of a park(SPCI: Surface Park Cooling Intensity) and parks with areas up to 16 hectares in the wider urban agglomeration of Athens. It is observed that the larger the area, the stronger the cooling effect of the park. When the correlation includes all parks regardless of size, however, it is observed that the cooling effect for parks larger than 16 hectares remains almost constant. This does not diminish the value of large green spaces but highlights the importance of dispersing small and medium-sized parks throughout the urban fabric (‘urban acupuncture’) as part of adaptation plans for urban heat mitigation. Figure 6 Correlation between the cooling effect of a park(SPCI: Surface Park Cooling Intensity) and the park’s area. SPCI vs park area(parks up to 16ha) SPCI vs park area(all parks) 6 6 5 5 4 4 SPCI (K) SPCI (K) 3 3 2 2 1 1 0 0 0 5 10 15 20 0 Park area(ha) 20 40 60 Park area(ha) Source: Remote Sensing Unit, Department of Environmental Physics, National and Kapodistrian University of Athens. Another interesting finding is that under intense heatwave conditions, many plant species tend to close the stomata of their leaves because of severe heat stress, minimising their cooling ability. This implies the need to select the right type of trees to endure during longer periods of high temperatures and heatwaves. Figure 7 shows the variation of SPCI depending on the type of greenery in a park. such as Paris 4 and Barcelona 5 to reduce air and land surface temperatures and, consequently, to address excessive heat due to climate change, also through bioclimatic interventions in school buildings. In cities with limited free spaces for creating parks, an alterna4 tive solution is to convert schoolyards into a network of small 5 parks. Such networks have been developed in European cities 5 OASIS project, https://www.uia-initiative.eu/en/uia-cities/paris-call3 Climate Shelters project, https://www.uia-initiative.eu/en/uia-cities/ barcelona-call3

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE Figure 7 Variation of SPCI(Surface Park Cooling Intensity) depending on the type of greenery in parks. 1. Parks with trees 2. Parks with grass 3. Mixed parks 4. Parks with shrubs& soil SPCI (°C) 2.5 2.0 1.5 1.0 0.5 0.0 Forest Grass Savannah Soil& Multi-use shrubs 5. Multi-use parks Source: Agathangelidis, I., Blougouras, G., Cartalis, C., Polydoros, A., Mavrakou, T., and Tzanis, C.G.(2023): Surface thermal effects of parks in Mediterranean cities: an investigation under typical summer conditions, heatwaves and droughts. 2023 Joint Urban Remote Sensing Event(JURSE), IEEE. https://ieeexplore.ieee.org/document /10144132 In a simulation experiment, a primary school in Athens 6 was examined in terms of its resilience to heat by applying a microclimatic model. The school’s redesign(Figure 8) included planting in the courtyard, creating a small park at the back of the school building, installing a green roof, designing shade structures and a green wall on the western side of the school, and finally placing cool(reflective) materials in the schoolyard to reduce absorbed solar radiation and, consequently, land surface and overlying air temperatures. Simulations(at noon) showed a decrease of air temperature of from 1 to 3°C in the schoolyard. Figure 8 Elements of a heat mitigation plan at the school level. Extensive green roof – light weight – low water plants for the dry climate – low maintenance Green wall – vertical green construction with soundproofing and evergreen trees Mediterranean park – evergreen drought tolerant trees, green patches for school gardening, an outdoor classroom Rainwater harvest system – rainwater storage tank Greener schoolyard – low water landscape Permeable paving system – rainfall soaks into the soil, preparing it for periods of drought – asphalt reduction Shade – natural shade: evergreen trees – constructed shade: retractable canopies or shade sails Source: Remote Sensing Unit, Department of Environmental Physics, National and Kapodistrian University of Athens. School building thermal upgrade – to minimize heat waste from the school Reflective surfaces – to be used with caution as it may reflect solar radiation back to school 6 114th Primary School in the Sepolia neighbourhood. 6

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE Another alternative solution is based on so-called‘super blocks’, namely city blocks in which vehicular traffic is restricted to the outer boundaries. The super blocks solution is being piloted in Barcelona in an effort to reclaim public space and, primarily, to enhance greenery in areas previously occupied by cars, thereby reducing air temperature and heat exposure. In practical terms, intersections are converted into green spaces, and only neighbourhood residents are permitted to use the roads within the perimeter. BLUE URBANISM The main impact of water surfaces on urban heat lies in their ability to cool the air through evaporation. Additionally, the high heat capacity of water surfaces leads to lower temperatures. The heat capacity of water is about four times greater than that of common building materials, such as concrete, asphalt, granite, gravel and marble. As a result, when absorbing the same amount of solar radiation, water exhibits a much smaller temperature increase than typical construction materials. Consequently, water surfaces can be considered heat sinks in urban spaces. width), the dispersion of small and medium-sized parks or green hubs in the urban fabric, and the creation of green roofs; – selecting high reflectivity(cool and super cool) materials for open spaces and the built environment; – promoting energy-retrofit actions in the built environment to improve heat insulation and reduce the use of air conditioners; – ensuring unobstructed airflow in urban ventilation routes; using semi-permeable surface materials to retain rainwater on the surface and facilitate the cooling process of evaporation; and – developing water collection areas(for example water ponds) to leverage their cooling effect. 3. Put vulnerable people first Priority application of urban heat mitigation plans is needed for low-income areas in which the impacts of heatwaves are more intense or where high concentrations of vulnerable groups(<10 years and>65 years) are recognised, or where critical infrastructures are located(for example, kindergartens/ schools, hospitals/health centres, and nursing homes, senior citizens centres, open cultural and sports facilities and so on). NEIGHBOURHOODS IN THE SPOTLIGHT The increased traffic of private and public vehicles in cities, because of the dispersion of social and commercial infrastructures and activities, leads to the production of anthropogenic heat and carbon dioxide emissions. Traffic is further exacerbated by the shrinking of the neighbourhood as the basic unit of citizen services, leading to trips outside the neighbourhood that could have been avoided. Innovative ideas, such as the 15-minute neighbourhood being implemented in Paris, are being implemented in the global transformation of cities to adapt to climate change. Such a neighbourhood offers comprehensive services within a 15-minute distance, from basic needs to entertainment and social services. HOW TO DRAW A HEAT ROAD MAP FOR URBAN CLIMATE RESILIENCE 1. Take note that urban heatscapes correlate strongly with the 3‘U’s: – Urban green(vegetation) – Urban form(3-D geometric properties) – Urban fabric(urban materials, land use and land cover) TAKEAWAY MESSAGES – Each urban area needs its own heat mitigation plan. No urban heat mitigation plan can be applied everywhere, indiscriminately. – Set the institutional framework and ensure the involvement of stakeholders in its shaping. – Conduct heat risk and vulnerability assessments on a detailed spatial scale to differentiate urban heat mitigation plans on the neighbourhood scale. – Engage local communities in the urban heat mitigation process, raising awareness of climate change and urban heat, and fostering local initiatives to enhance just resilience. – Develop a monitoring and evaluation system for early assessment of the performance of the heat mitigation measures. – Take note of the risk of maladaptation, namely when a heat mitigation plan creates new risks and negative consequences instead of reducing vulnerability. 2. Exploit measures to shape an urban heat mitigation plan in cities by: – reducing anthropogenic heat sources, mainly through limiting vehicular traffic, especially in central areas; – converting streets in which building height significantly exceeds street width into pedestrian networks or low-traffic roads, combined with detailed traffic studies to avoid transferring traffic to other areas; – enhancing greenery through extensive tree planting on road axes and burdened roads(for example, streets in which building height significantly exceeds street 7

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE REFERENCES Agathangelidis, I., Cartalis, C., Santamouris, M.(2019): Integrating Urban Form, Function, and Energy Fluxes in a Heat Exposure Indicator in View of Intra-Urban Heat Island Assessment and Climate Change Adaptation, in: Climate 2019, 6( 7), 75. Available at: https://doi.org/10.3390/ cli7060075 Agathangelidis, I., Blougouras, G., Cartalis, C., Polydoros, A., Mavrakou, T., and Tzanis, C.G.(2023): Surface thermal effects of parks in Mediterranean cities: an investigation under typical summer conditions, heatwaves and droughts. 2023 Joint Urban Remote Sensing Event(JURSE), IEEE. Available at: https://ieeexplore.ieee.org/document/10144132 Paravantis J., Santamouris M., Cartalis C., Efthymiou C., Kontoulis N.(2017): Mortality Associated with High Ambient Temperatures, Heatwaves, and the Urban Heat Island in Athens, Greece, in: Sustainability 2017, 9(4), 606. Available at: https://doi.org/10.3390/su9040606 8

FRIEDRICH-EBERT-STIFTUNG – TURNING DOWN URBAN HEAT – CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE ABOUT THE AUTHOR IMPRINT Constantinos Cartalis is Professor of Environmental and Climate Physics at the National and Kapodistrian University of Athens and Member of the European Scientific Advisory Board on Climate Change. Friedrich-Ebert-Stiftung Athens Office Neofytou Vamva 4| 10674 Athens| Greece Responsible: Regine Schubert| Director Phone:+30 210 72 44 670 https://athens.fes.de Email: info.athens@fes.de Commercial use of all media published by the Friedrich-EbertStiftung(FES) is not permitted without the written consent of the FES. The views expressed in this publication are not necessarily those of the Friedrich-Ebert-Stiftung or of the organizations for which the authors work. 978-618-5779-11-5

TURNING DOWN URBAN HEAT- CHALLENGES AND PROSPECTS FOR URBAN CLIMATE RESILIENCE Cities are vulnerable to excessive heat associated with climate change(longer periods of high temperatures and heatwaves that are more frequent and of higher duration and intensity) because of their high population density, infrastructure and dense built-up areas. Appropriate measures to mitigate urban heat need to consider the‘vibe’ of a city, as well as its urban functions, urban form and urban fabric. Only with this knowledge is it possible to develop specific urban heat mitigation plans for each urban climate zone, to maximise the results of interventions and to avoid projects with limited or almost no impact. Particular attention should be paid to the relationship between income and exposure to heat. Households with lower incomes are more exposed to heat, mainly because of the moderate or poor quality and age of the buildings they tend to inhabit, the higher density of heat sources in their vicinity and/or the lack of green spaces. It is therefore necessary to prioritise the application of urban heat mitigation plans in these areas. The successful implementation of an urban heat mitigation plan depends, among other things, on establishing the necessary institutional framework and involving stakeholders. The involvement of local communities in the urban heat mitigation process is essential to raise awareness of climate change and to promote local initiatives for equitable resilience. Further information on the topic can be found here: www.fes.de/stiftung/internationale-arbeit