Combating the heat island effect Using green infrastructure to mitigate excess urban heat Jason Beringer, Nigel Tapper, Andrew Coutts and Margaret Loughnan Centre for Water Sensitive Cities School of Geography and Environmental Science Monash University, Melbourne, Australia
Overview 1. Excess warming in urban areas (UHI and urban climate) 2.Basics of urban climate and the UHI 3.How can fit-for-purpose water sources provide multiple benefits? 4.Cities as Water Supplies Catchments research program 5.Current research on the effectiveness of green infrastructure. Neville Bowler
A Global Perspective on Temperature Trends Last 25 years 1. Urban climate influenced by: Historical and future climate Climate variability Urbanisation 3. Urban warmth similar magnitude to predicted global warming 4. Effects are additive! 5. Climate change requires mitigation and adaptation Future projections IPCC 4AR, 2007
The Urban Heat Island (UHI) Climate varies between cities and neighbourhoods Land surface temperatures Night-time surface UHI Urban heating during day but temperature variability evident Max UHI ~4 o C Local hot/cool spots ~1-2 o C DHS, 2009 Heatwave Plan for Victoria 2009 2010 Night Day
The Urban Heat Island (UHI)
Urban Radiation and Energy Budget Simply Explained Radiative energy available at the surface (Q*) + artificially produced energy (Q F ) = energy used in heating the air (Q H ) + energy used in heating materials (Q S ) storage + energy used in evaporating moisture (Q E )
Causes of Urban Warmth 1. The nature of surface materials (i.e. thermal characteristics and albedo of surfaces). 2. Surface shapes and structures (the complex nature of urban geometry) 3. Alterations in urban air quality 4. The presence of heat sources (cars, industry, HVAC, metabolic heat, etc.) 5. Vegetation removal 6. Surface waterproofing and especially removal of urban storm water Can fit for purpose water supply help???
Rural to Urban contrast
Perth Melbourne Water security in Australian cities Drought conditions are putting increasing pressure on urban water supplies Record low inflows into city water storages Possible links to climate change: e.g. indication that the decline in SE Australian rainfall related to increasing intensity of the subtropical ridge with climate change (SEACI, 2008) Desalination plants Melbourne: 150GL per year from end of 2011 State Government Water Plans Diversity of supply Melbourne Water 2010 W.A. Water Corp.2010 Can fit for purpose water supply help???
Response to dry conditions Water restrictions Various stages that limit water in the urban landscape. Water wise gardens Vic. Gov. 2010 Aim to minimise water use in gardens Drought tolerant plant species Impacts Very dry urban soils Harder to re-wet Reduced evapotranspiration Existing vegetation cannot cope: stressed trees and reduced shading Exacerbates dryness and heat Can fit for purpose water supply help??? DHS, 2009 Heatwave Plan for Victoria 2009 2010
Mitigation of excess urban heating Strategies are required to reduce the impact of negative urban climate impacts of the urban heat island. Mitigation could include: 1. Higher surface and rooftop albedos 2. Improved energy efficiency 3. Green infrastructure Sufficient amount of open space (limited) Increased vegetation cover and shade trees WSUD technologies, wetlands, open water, green roofs and walls, biofilters, swales, etc. Green infrastructure supported by fit for purpose water supplied from widespread water retention strategies. For example, stormwater.
Stormwater harvesting The reason we need drought proof gardens is because we export our stormwater We can implement stormwater harvesting technologies and WSUD to retain water in the urban landscape. Potential to: Provide low energy, fit-for purpose water - augment city water supplies Support green infrastructure and Enhance urban climates. Provide Multiple benefits www.urbanstreams.net/rpad/melbrunoff.html FAWB, 2010
Multiple benefits of green infrastructure Alleviate Urban Heat Island (offset urbanisation and global warming) Changed water regimes Reduced stormwater runoff Improved river health and biodiversity Restore natural flow regimes and soils moisture levels Provide flood protection Enhanced vegetation Increased air pollution removal Increased carbon sequestration Improved urban biodiversity Energy savings Reduced public health issues/costs Support improved urban amenity www.melbourne.vic.gov.au/
Cities as Water Supply Catchments Program Program is aimed at: Mainstreaming stormwater harvesting and Water Sensitive Urban Design to deliver multiple benefits Demonstrating that it is safe, practical and cost effective Enhancing the liveability of our urban environments Project outline Project 3: Green cities and microclimate assess the micro-climatic and liveability advantages of WSUD & stormwater management solutions www.watersensitivecities.org.au/
Temperature ( o C) Climatic advantages of green infrastructure Evaluate effectiveness of WSUD/green infrastructure in reducing excess urban heat. Including; Green roofs/walls Radiation balance Surface temperatures Temperature gradient and heat flux through roof Compare with cool roofs (benchmark) 50 40 30 20 Tin Soil Veg 10 0 Time
Climatic advantages of green infrastructure Evaluate effectiveness of WSUD/green infrastructure in reducing excess urban heat. Including; Green roofs/walls
Climatic advantages of green infrastructure Evaluate effectiveness of WSUD/green infrastructure in reducing excess urban heat. Including; Green roofs Vegetated stormwater treatment raingardens ET using chambers Thermal efficiency Spatial influence Water balance
Climatic advantages of green infrastructure Evaluate effectiveness of WSUD/green infrastructure in reducing excess urban heat. Including; Green roofs Vegetated stormwater treatment Street trees Effectiveness for improving HTC through cooling and shade Prominade Neighbourhood street
Climatic advantages of green infrastructure Evaluate effectiveness of green infrastructure in reducing excess urban heat at neighbourhood scale. Mawson Lakes field campaign Feb 2011 Childcare Playground Train/Bus station Focus on effectiveness of WSUD elements School Land use classes Include areas high vulnerability and exposure HTC observations Static stations Mobile traverses Thermal images HTC surveys Transects Remote sensing
Provide stormwater harvesting strategies for MULTIPLE BENEFITS Use GIS based tools (CITY Green) Identify multiple benefits of urban trees on; Air quality Stormwater infrastructure Carbon sequestration Social Cost of Carbon for the carbon stored and annually sequestered within the two PACs for the present state, Melbourne 2030 and extensive tree cover scenarios. Ringwood PAC Greensborough PAC Storage Sequestration Carbon Sequestration Scenario ($AUD.ha -1 ) ($AUD.yr -1.ha -1 ) ($AUD.ha -1 ) ($AUD.yr -1.ha -1 ) Current 1003.5 6.3 1872.9 12.3 Melbourne 2030 936.5 5.8 3222.8 20.7 Extensive tree cover 4934.5 31.0 5146.0 31.8
Value