Economic valuation of UHI mitigation and other environmental benefits of urban street trees Jasmine Thom and Andrew Coutts
BACKGROUND
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WHAT DO WE KNOW?: URBAN CHALLENGES
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
TRESS MAY MITIGATE URBAN CHALLENGES
THROUGH ECOSYSTEM SERVICE PROVISION
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WHAT DO WE KNOW?: BENEFITS OR URBAN TREES
• Many ecosystem services provided by trees • Tangible services are economically quantifiable • Available tools such as i-Tree can conduct economic analysis • Gap in research methodologies is the valuation of heat mitigation
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
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RESEARCH AIMS AND QUESTIONS
What are the current environmental and economic benefits of ecosystem services provided by street trees in the City of Monash?
How would three urban planning policy scenarios influence ecosystem service provision? 1) An increase in the street tree population 2) A decrease in the street tree population 3) A decrease in the health of the street tree population
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
NEED TO UNDERSTAND
TRADEOFFS AND OPPORTUNITY COSTS OF DEVELOPMENT TO
FOSTER SMART GROWTH
RESERCH APPROACH
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STUDY AREA
The City of Monash was used as a case study
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
Population of 177,300, 17% aged over 65 2031 population projections: - Additional 13,300 dwellings and 31,200 residents
A recent inventory of public trees available (2013-2014)
Measurement of street tree canopy dimensions in the City of Monash
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RESEARCH APPROACH: Economic Valuation
Economic values adjusted for inflation and converted to AUD using PPP exchange rate Pollution benefits: valued from external pollution costs Carbon benefits: valued from recommended carbon price Stormwater benefits: valued as avoided stormwater infrastructure costs Heat mitigation benefits: valued using VSL for Australian policy appraisal
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
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RESEARCH APPROACH: I-Tree Modelling
Sampled tree characteristics of 1 % (1,284 trees) of the Monash Tree Inventory
Scaled sample characteristics to entire population
Created three scenarios for modelling
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
Measurement of street tree diameter at breast height for input into i-Tree
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RESEARCH APPROACH: Climate Modelling
Economic value of Heat mitigation: Δ(predicted mortality) x VSL
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
Change in predicted mortality relative to maximum air temperature
Estimated proportion of land covered by public trees
Estimated change in air temperature during 2009 heatwave
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ALTERNATIVE SCENARIOS
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Scenario Change i-Tree Modelling Climate Modelling
Increased Trees + 100% Double tree population No change in structure
Double public tree cover fraction
Decreased Trees - 50% Randomly remove 50% of tree population
Half public tree cover fraction
Poor Health - 50% Reduce Canopy area (represent leaf dieback)
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KEY FINDINGS
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TOTAL ECONOMIC VALUE
TOTAL VALUE: $ 12.85 Million Pollution: $ 800,566 yr-1
2,241 kg yr-1
Carbon Storage: $ 1,984,455
19807 t (0.23 tree-1) Sequestration: $ 149,507
1,492 t (17 kg tree-1)
Stormwater: $ 126 809 20,033 m3 yr-1 (0.2 m3 tree-1)
Heat: $ 9,788,505 -0.48 to 0.51°C; 2.3 lives ‘saved’
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
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ALTERNATIVE TREE COVER Increased Pollution, carbon
stormwater benefits increased 100%
$3 million increase
Decreased Pollution, carbon,
stormwater benefits decreased 50%
$1.5 million decrease
Poor Health Decrease pollution (30%)
carbon sequestration (24%) and stormwater benefits (17%)
$300,000 decrease
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THE EFFECT OF ALTERNATIVE SCENARIOS
Current trees Decrease Ta 0.51°C Decrease mortality by 2.3 $9.7 million Increased trees Decrease Ta 0.57°C Decrease mortality by 1.5 $6.3 million (+64%) Decreased trees Increase Ta 0.3°C Increase mortality by 1.1 $4.6 million (-49%)
MONASH EARTH, ATMOSPHERE & ENVIRONMENT
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INFORMING POLICY AND PLANNING
Increased quality canopy cover may increase economic value considerably
Decreased canopy cover had proportional loss in economic value – May have additional re-establishment costs once they are lost
Poor tree health scenario did not consider heat benefits – change in value much lower – does not consider loss in aesthetic value or possible loss of trees from poor health
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KNOWLEDGE GAPS AND FUTURE RESEARCH
i-Tree • how sampling method used relates to
standard sampling method
Climate modelling • More sophisticated climate modelling e.g. 3D
urban canopy layer for modelling air heat mitigation.
• Inclusion of changes in tree health to climate modelling (e.g. LAI change)
• Estimation of UHI mitigation from design intervention at different spatial scales
• Modelling health effects over longer time periods
• Economic value could be divided into annual returns relative to probability of event occurring
Economic Valuation • Uncertainty in VSL
• Uncertainty in exposure-response functions
• Economic values not specific to Australia
• Future value unknown, likely to change over time
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Urbanisation impacts urban populations through pollution, carbon emission, increased stormwater and excess heat Protecting and increasing healthy urban trees is one way of addressing these impacts Balancing maintenance and canopy cover decisions within budget constraints requires an understanding of the value and benefits of trees.
Economic value of urban trees is considerable. Urban design decisions impact environmental and economic value of trees
i-Tree model can be used to value ecosystem services of trees from random sampling and existing tree inventories
Economic value of heat mitigation can be estimated by relating change in air temperatures to predicted mortality and an established VSL
CONCLUSIONS
MONASH EARTH, ATMOSPHERE & ENVIRONMENT