Effects of California's Urban Forests on Energy Use and Potential Savings From Large-Scale Tree Planting
Tree canopy cover data from aerial photographs of 21 California cities and building energy simulations were applied to estimate effects of existing trees and new plantings on energy use in 11 climate zones. There are approximately 177.3 million (se 2.8 million) energy-conserving trees in California communities and 241.6 million (se 3.2 million) empty planting sites. Existing trees are projected to reduce annual air conditioning energy use by 6,408 G\Vh (2.5%) with a wholesale value of $485.8 million. Annual cooling savings are of similar magnitude to the amount of electricity consumed by 7.3 100 MW power plants or 730,000 homes. Peak load reduction by existing trees saves utilities 5,190 MW (10%) valued at approximately $778.5 million annually, or $4.39/tree. Planting 50 million trees to shade east.and west walls of residential buildings is projected to reduce cooling by 46,981 GWh (1.1%) and peak load demand by 39,974 GW (4.5%) over a 15-year period. The present value (wholesale) of annual cooling reductions for the 15-year period is $3.6 billion ($71/tree planted). The annual cooling savings after 15 years of growth (7.3-m tall trees) is 6,092 GWh ($421 million), substantially more than the 5,000 GWh forecasted annual increase in consumption associated with 550,000 new residents and changing energy-use patterns. Cooling savings are greatest in the south valleys, central coast, south coast, and inland empire. On a per tree planted basis, cooling savings are greatest in the desert, inland empire, south valleys, and central valley climate zones. The implications of regional differences in tree planting potential and cooling savings for developing cost-effective shade tree programs are discussed.
Keywords: urban forests, peak load reduction, energy conservation