Doick, Kieron

University of Birmingham Research Archive, E-papers Repository

The role of trees and greenspaces in mitigating urban heat islandsDr Kieron J. DoickDr Madalena Vaz MonteiroUrban Forest Research GroupForest ResearchMember of:TDAG (Trees and Design Action Group)04/04/20192Scene settingLand Regeneration Urban Trees and GreenspaceRemediationSpecies selection Ecosystem service provision Process Quantification and valuation= Decision makingProvisioning Regulating Supporting CulturalClimate regulationAir pollutionStorm-water capturei-Tree04/04/20193Urban cooling by trees and GS1. Cooling by one large Greenspace (Kensington Gardens)2. Cooling by greenspaces of various sizes3. A study into pan-city cooling4. ‘Research Notes’ 5. Cooling by street trees6. Valuing cooling7. Species selection for cooling- (a little bonus for you)Urban Heat Island abatement by greenspacesA study of Kensington gardens04/04/20195IntroductionThe Urban Heat Island (UHI)“higher mean average temperature in cities than  surrounding countryside”UHI = Temp(Urban)- Temp(Rural)First reportedby Luke Howardin… 1820Ref: GLA (2006) London's urban heat island: A summary for decision makers04/04/20196Introduction (cont.)Nice and warm, so why the fuss…• UHI intensity can be as much as 9oC (may be more)• There is a direct and significant impact of heat on human health…• ~ 1,100 heat-related deaths and 100,000 hospital patient-days per year in the UK• …plus 10s to 100s more deaths per heat wave• 30th June to 2nd July 2009 = 299 excess deaths in England• Combined effect of climate change and UHI• Climate change scenarios are for rural setting• Multiple cooling mechanisms from vegetation; these are additive and is significant enough to impact at the city scale04/04/20197Key:  Q* = Solar radiation; QF = Anthropogenic heat; QH = Sensible heat flux (heated air);     QE = Latent heat flux; (energy used in evaporating or transpiring water); ΔQS = Heat storage within the environment; ΔQA = Net advective (horizontal) heat fluxTranspiration > Reflection of solar radiation > ShadingShadingReflectionTranspiration04/04/20198Solar radiationSensible heatLong-wave radiationHeat storageOne solutionTranspirationShadingHeat storageSolar radiationSensible heatLong-wave radiationGreen infrastructure can mitigate UHI04/04/20199MethodologyRoad Transect 2:Gloucester TerraceRoad Transect 1:QueenswayKey:O = open spaceG = grassT = tree04/04/201910Methodology (cont.)Craven RoadWestbourne CrescentSouth SideNorth SideABCFDEGHIJKLLancaster GateKey:South: A, B, C, D, E, F,North: G, H, I, J, K, LTrees: A, E, G, ILamp posts: B, C, D, F, H, J, K, LIntersections: A, F, G, LSensor Locations along Gloucester Terrace Transect04/04/201911Methodology (cont.)04/04/201912ResultsComparison of air temperatures (four locations within Gloucester Terrace; one 24-hour period)11121314151617181920212223240 2 4 6 8 9 10 11 12 14 16 18 20 22Time, hoursAir Temperature, oCIntersectionLamp postStreet trees04/04/201913Results• Streets significantly warmer than the average temperature across Kensington Gardens• Hard-standing area (only) of Kensington Gardens not significantly warmer than Streets• Grassed area of Kensington Gardens  significantly warmer than the tree-lined area in August and September • Street canyons not significantly warmer than intersections• Air temperature below street tree canopies not significantly cooler than lamp-post (24hr mean)• p<0.05 or p<0.0104/04/201914ResultsVariation in heat island intensity at mid-point along  Gloucester Terrace transect (August)-4-2024680 2 4 6 8 10 12 14 16 18 20 22 24Time, hoursHeat Island Intensity, K C04/04/2019150510152025303540-3 -2 -1 0 1 2 3 4 5 6Heat Island Intensity, K% timeA0510152025300 1 2 3 4 5 6 7 8Heat Island Intensity, K% timeB0510152025303540-3 -2 -1 0 1 2 3 4 5 6Heat Island Intensity, K% timeC0510152025300 1 2 3 4 5 6 7 8Heat Island Intensity, K% timeDDay timeNight timeKensington GardensFrequency Distribution plots…Gloucester Terrace04/04/201916ResultsAnalysis of heat island intensity at various locations across London• Max and Min’s are the largest and smallest hourly UHI value observed in a month• Mean values are for the monthC04/04/201917ResultsModelled temperature gains with increased distance from Kensington GardensModelling used mean under street tree heat island values relative to the under tree temperatures in Kensington Gardens Ambient temperature (oC)8121620-0.20.00.20.40.60.81.01.20 50 100 150 200 250Distance, mTemperature, KAC04/04/201918Relationship between urban heat island intensity and increased distance from Kensington Gardens on 9 AugustPark cooled the transectwhen cooling was mostneeded, on warm calmnightsCooling of up to 4°Cover 440 m distancefrom the park wasobserved on singlenightsResults 201104/04/201919ResultsFrequency distribution of daily mean average temperatures0102030405060Wisley Rush Green St James' Park Gloucester Terrace Queensway Kensington GardensLocationCumulative No. of Days0102030405060Wisley Rush Green St James' Park Gloucest r Ter ace Que nsway Kensington G rdensLocationCumulative No. of DaysLocationKey: Black bars <0oC Up-diag. 0-5oC Horizantals 5-10oCDown-diag. 10-15oCVerticals 15-20oCSquare hatch >20oC04/04/201920Implications• Urban dwellers are exposed to warmer temperatures for longer periods than people living in the countryside• It is cooler close to a large greenspace than [say] 200-300m away; street trees offer some protection too• Impact of cooling by large greenspaces may be lowest when needed the most• Dormancy and frosting of urban trees/ green-spaces is slight and (possibly) decreasing• Forecast climate = increasing social and environmental pressures on greenspaces (climate and biotic pressures)04/04/201921Future WorkMore questions• Impact of…  …on cooling effect• greenspace size• greenspace design (relative proportions of hard surfaces, grass and trees)• Cooling boundary: what governs…• Shape• Size• Permanence • Penetration into surrounding areas (role of street canyons vs. buildings as barriers to air movement) 04/04/201922Future Work• Cooling by vegetation vs. thermal comfort• Valuing the cooling effect of • street trees• green spaces• green infrastructure• Species selection foroptimised cooling (given urban setting,climate change)• How to position streettrees for optimal coolingUrban Heat Island abatement by greenspacesA study of Cooling by Greenspaces of various sizes04/04/201924ProjectsThe role of greenspaces in mitigating London's UHIIn 2011• Air temperatures measured in one of central London's large greenspaces and in an adjacent street • Aiming to determine the extent to which the greenspace reduces UHIDoick et al., 2014. Science of the Total Environment 493: 662–671In 2012• Air temperatures measured in and around eight London greenspaces, with areas ranging from 0.2 to 12.1 ha• Aiming to define the relationship between cooling extent and the size of greenspaceVaz Monteiro et al., 2016. Urban Forestry & Urban Greening 16: 160–16904/04/201925Study areas 2012Key: 1. Acton Park, 2. Queen’s Park, 3. Russell Square, 4. Grosvenor Gardens, 5. Vincent Square, 6. Lincoln's Inn Fields, 7. Ebury Square Gardens and 8. Warwick Square (© Crown copyright and database right [2015] Ordnance Survey [100021242])04/04/201926A. very small greenspace (Grosvenor Gardens, 27 June)B. small greenspace (Russell Square, 20 September)C. medium greenspace (Queen’s Park, 18 August)Very small greenspaces (area <0.5 ha)did not affect the air temperatures of theirsurrounding areasSmall greenspaces (area 0.8 to 3.8 ha)cooled by an average of 0.4 to 0.8oC overapproximately 30 to 120 mMedium greenspaces (area 10.1 to 12.1ha) cooled by an average of 0.6 to 1.0oCover approximately 180 to 330 mModelling of cooling extent was statistically valid onlyon calm warm nights (≥ 10oC and wind speed ≤ 3 m/s)Results 201204/04/201927Cooling distance increased linearly with increasing area ofgreenspace but the relationship between area and theamount of cooling was non-linearResults 201204/04/201928Greenspaces with area >0.5 ha can reduce the air temperaturesof their surrounding areas during warm and calm nightsAmount of cooling provided increases with area of greenspaceProjects0.00.51.01.50 50 100 150 200 250 300 350 400 450 500Temperature change  (oC)Distance from greenspace (m)Large greenspaceMedium greenspaceSmall greenspaceUrban Heat Island abatement by greenspacesA study into pan-London cooling04/04/201930Cooling boundariesSize Cooling DistanceReferenceVerysmall(≤ 0.5ha)10 - 20 m 1-2oC cooling for 20 m, 0.24 ha park in Kumamoto City, Japan (Saito et al. 1990)Cooling boundary approximates to greenspace width (Yu & Hien, 2006: mathematical model).Small(0.5-1 ha) 50 –150 m1.5oC cooling for 150 m, 0.5 ha park in Haifa, Israel (Givoni 1998)0.30oC cooling for 80 m around green sites of width 20 – 60 m) in Tel Aviv, Israel (Shashua-Bar and Hoffman 2000).Medium (2- 100ha)200 –1000 m0.9oC cooling for 30 m, 3.6 ha park in Goteborg, Sweden (Upmanis et al. 1998).1.5oC cooling for 1 km, 60 ha park in Tama New Town, Japan (Ca et al. 1998)3oC cooling for 50 m around parks of up to 27 ha in Fukuoka City, Japan (Katayama et al. 1993)Large(>100 ha) 400 –2000 mChapultepec Park (500 ha) in Mexico City cooling distance ca. 2 km (Jauregui 1991).4oC cooling over 775 m, 156 ha park in Goteborg, Sweden (Upmanis et al. 1998).04/04/201931Cooling boundariesFTC Description Type1 Building Artificial2 Man-made surfaced area Artificial3 Vegetated/natural area – predominantly grass and low vegetationGrass4 Water Blue space5 Man-made structure other than building Artificial6 Vegetated/natural area – scattered trees (>30% and <70% cover)Greenspace7 Vegetated/natural area – predominantly trees (>70% cover)Greenspace8 Not used9 Non geographic entity typeFTC = feature type code04/04/20193204/04/20193304/04/201934Results (1)London BoroughArea Cooled Population Age Sex HealthInner London (Ha) (%) TotalUn-cooled <4 5-74. >75 Males Females Good FairNot GoodCity of London 13 4.0 7.4 6.5 0.2 6.7 0.4 4 3 6.5 0.6 0.2Tower Hamlets 278 12.9 254 229 17.9 218 7.1 125 118 202 25.9 14.7Hammersmith and Fulham 247 14.4 182 175 11.1 153 6.8 83 88 146 16.1 8.3Lambeth 395 14.5 303 278 19.2 252 9.8 140 141 239 28.9 13.2Hackney 337 17.7 246 227 17.8 204 7.2 114 116 190 25.0 14.2Islington 268 18.0 206 176 11.2 169 7.4 93 96 155 21.1 12.1Newham 741 19.2 308 272 22.5 242 8.1 142 131 227 30.9 15.4Kensington and Chelsea 301 24.3 159 134 8.3 128 7.4 71 73 124 13.1 6.5Camden 535 24.5 220 205 12.0 179 10.1 99 103 169 21.0 11.3Southwark 761 25.4 288 253 18.3 226 9.1 126 128 215 26.4 12.5City of Westminster 743 33.7 219 189 10.5 162 9.4 93 89 153 18.3 10.6Lewisham 1,237 35.0 276 206 17.2 189 9.8 106 110 179 25.3 11.2Wandsworth 1,261 35.8 307 248 17.6 221 10.1 121 128 217 22.1 9.4Greenwich 1,934 38.3 255 192 16.1 170 9.6 97 99 163 22.6 10.5Totals 9,050 26.0 3,232 2,790 200 2,522 112.3 1,411 1,423 2,387 297 150Population figures are ‘thousands’. ‘Cooled’ populations refers to those people living within an area cooled by a 2oC cooling boundary and or multiple cooling boundaries04/04/201935Results (2)Scenario CI 5% No. deaths CI 95%ModelledWith current cooling 107 145 184Assume: no cooling 124 168 2121°C Cooling pan-London 62 83 1062°C Cooling pa-London 26 35 44PresentLives saved with current cooling 17           (124-107=)23(168-145=)29Value (£) £29.1 million £39.3 million £49.8 millionLives saved with 2oC  cooling across London 98 133 168Value (£) £171 million £232 million £294 millionNo. of deaths in a heatwave values from Hajat et al. (2002)Urban Heat Island abatement by greenspaces‘Research Notes 12 And 37’RN12 “Air temperature regulation by urban trees and green infrastructure” published in Feb 2013Research Notes37• Draws together scientific evidence to outline the:• causes of urban heat islands• role of trees and wider green infrastructure in combating UHI• effects of urban heat islands on human health• Impact of vegetation (mechanisms of cooling)• Spatial scales of cooling• The right tree in the right place• Tree selection• Tree location• Other adaptations to mitigate UHI• Potential conflictsRN37 “The role of urban trees & green spaces in mitigating urban heat islands” published in JanResearch Notes38RN37Research Notes39• Cooling across the entirety of an urban area requires greenspaces to be closely spaced• Greenspaces should be treed, but care is required in the placement of trees • Some trees are better at cooling• shape and size• transpiration rates• reflectivity• larger canopies(provided they are healthy and have enough space, soil water and nutrient resources to maintain their growth)• The tree’s aerial and soil environment is as important as the tree itselfCooling by street trees04/04/201941ProjectsThe role of street trees in improving thermal comfort in Bristol• Two streets have been selected for a pilot study: Freemantleroad (220 m long, 20 m wide) with mature street trees andGlen Park (150 m long, 15 m wide) with no street trees.• Mobile weather station measuring incoming solar radiation,air temperature and humidity at 2 m height.04/04/201942ProjectsValuing coolingValuing cooling by urban forests• Climate regulation is one of many ‘ecosystem services’ provided by the urban forest• Value it? (like for carbon sequestration, and air pollution removal)• i-Tree Eco estimated urban forest composition• Quantified estimation of evapotranspiration• TRNSYS and TRNFLOW modelling(dynamic building thermal and airflow modelling programs)04/04/201944Valuing cooling by urban forests• Energy savings to air-conditioned of buildings• Trees shown to provide substantial cooling• A modelled 1.3 –13.4% reduction in air-conditioning unit energy consumption • Equivalent to £2.1m to £22m in electricity costs• Key species:• Castanea sativa• Prunus avium• Quercus petraea• Platanus hybrida• Fagus sylvatica04/04/201945Species selection for cooling4-Apr-1947How do you select trees for cooling?The solutionThree equations are proposed that allow comparison of the relative abilities of trees to cool Transpiration = crown diameter * LAI a * canopy aspect ratio * stomatal conductance bReflection = albedo * crown diameter * LAI Shading = crown diameter * LAI * tree heightcanopy aspect ratio Where: a LAI = leaf area index; b stomatal conductance (or: growth rate)Species selection for cooling48A cooling index of urban trees49A cooling index of urban trees4-Apr-1950A cooling index of urban treesHow to use the equations• Start with a short list of species/cultivars suited to the location (remembering scenarios 10-14)• Apply actual, estimated or relative values to each parameter in Equations 4 to 6 for each of short-listed options• (assume) that the tree species that scores highest in relation to all three cooling mechanisms will be more effective at providing urban cooling.• Consider need/desire to balance other benefits, e.g. contribution to sense of place, biodiversity 04/04/201951i-Tree Canopy:can you help us build an Urban Canopy Cover map for the UK?53What it looks like to get involved….visithttps://www.forestresearch.gov.uk/research/i-tree-eco/urbancanopycover/for our step-by-step guide and to learn about the project aims and objectives4-Apr-19i-Tree Canopy4-Apr-1954The ‘Map’ and ‘Results’ pageStep-by-step, the guide4-Apr-195556 4-Apr-19i-Tree Canopy4-Apr-1957What does it look like…Results4-Apr-195804/04/201959The end…My thanks to…The Royal Parks, the Royal Borough of Kensington and Chelsea, and the City of Westminster for permissionsMadalena Vaz Monteiro, Phil Handley, Kathryn Hand, and former Group members: Ros Bryant, Vicki Lawrence and Andy BruntAndrew Peace, Paul Taylor and Paul Henshall for help with statistics and data processingThe Forestry Commission for funding

TDAG Mids Apr Meeting: The role of trees and greenspaces in

mitigating urban heat island, Kieron Doick, Forest Research

http://epapers.bham.ac.uk/3211/1/Trees_and_GS_for_urban_cooling_TDAG_Midlands_talk_020419.pdf

TDAG Mids Apr Meeting: The role of trees and greenspaces in mitigating urban heat island, Kieron Doick, Forest Research

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