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

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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

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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

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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

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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

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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

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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

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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’

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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%)

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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

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