Using Watered Landscapes to Manipulate Urban Heat

Island EffectsPatricia Gober

Decision Center for a Desert CitySchool of Geographical Sciences

School of SustainabilityArizona State University

A Community of Ecosystem Services Conference

Sheraton Wild Horse PassDecember 8, 2010

2 m Air Temperature SimulationsSpatial resolution = 2 km

Phoenix is beset by an expanding and intensifying Urban Heat Island

Source: Susanne Grossman-Clarke

Spatial Variations in Temperature

Oasis City

Irrigated vegetation increases nighttime cooling.

Climate Change Threatens Water Resources in Phoenix

Lake Mead (December 8) Water Level=1082.8 ft; 38% capacity

Classic Sustainability Challenge—tradeoff between water

conservation and temperature amelioration.

Local-scale Urban Meteorological Parameterization Scheme (LUMPS)

Linked equations to calculate heat fluxes at the neighborhood level.Uses standard meteorological

observations and basic knowledge of land coverPartitions energy balance as follows:

Q* = QH + QE + ΔQS

LUMPS Input: Land Cover

LUMPS key metrics daily ET [kgm-2] assumed to be equivalent to outdoor water

use

hourly daytime heating rate [°C] calculated for 12pm, MST

hourly nighttime cooling rate [°C] calculated for 8-10pm, MST

cooling efficiency [°C/kgm-2] nighttime cooling rate/daily ET

Gober et al. 2010. Using watered landscapes to manipulate urban heat island effects. Journal of the American Planning

Association 76(1): 101-121.

There is no one design and landscape plan capable of addressing increasing UHI and climate effects everywhere.

Study Areas

Wet fraction and LUMPS output

Cooling efficiencies improve under highly vegetated Scenario 1 (A), but worsen under

xerification Scenario 2 (B).

Climate Change Scenario-HADcm

LUMPS Output Base Case HadCM

Phoenix

Daily ET 1.931 1.975

Cooling Rate -0.171 -0.139

Heating Rate 0.768 0.761

Efficiency -0.073 -0.054

Portland

Daily ET 1.847 1.957

Cooling Rate 0.236 0.330

Heating Rate 0.644 0.632

Efficiency 0.156 0.198

Key Findings/Final Thoughts

Water conservation in both Phoenix and Portland will come at the costs of delayed and reduced nighttime cooling.

Reductions in outdoor water use in heavily vegetated neighborhoods (a spatially explicit policy) would minimize these deleterious consequences.

Portland will have more difficulty maintaining its current vegetation under climate change.

Cooling conditions in both cities are far more sensitive to changing land cover than to climate-change conditions, suggesting that interventions may be possible to mitigate UHI and facilitate climate adaptation.

Energy-water nexus—what are the energy savings from temperature reduction?

Questions?