ARB Research Seminar

This page updated May 21, 2015

Deriving Roof Albedo for Seven California Cities Using Remote Sensing

Photo of George Ban-Weiss

George Ban-Weiss

Photo of Ronnen Levinson

Ronnen Levinson

Photo of Jordan Woods

Jordan Woods

George Ban-Weiss, Ph.D., Astani Department of Civil and Environmental Engineering, University of Southern California; Ronnen Levinson, Ph.D., Lawrence Berkeley National Laboratory; and Jordan Woods, University of California, Berkeley

June 11, 2015
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


Cool roofs reflect sunlight and therefore can reduce cooling energy use in buildings. Further, since roofs typically cover about 20-25% of a city, widespread deployment of cool roofs could mitigate the urban heat island effect and partially counter urban temperature increases associated with global scale climate change. The magnitude of these potential benefits for a given city depends on the increase in albedo that can be achieved using reflective roofs. Assessing this increase requires knowledge of roof albedo at the city scale, which until now has been hindered by a lack of reflectance data with sufficient spatial coverage, spatial resolution, and spectral detail.

In this work we use multiband remotely sensed imagery to derive the albedos of individual roofs in seven California cities: Los Angeles, Long Beach, San Diego, Bakersfield, Sacramento, San Francisco, and San Jose. This presentation will describe the developed methods, the associated uncertainty in derived values, city-wide roof albedos attained for each city, and potential impacts of widespread adoption of cool roofs. The main findings of this research are (a) the city-wide mean roof albedos for the cities investigated are low, ranging from 0.17 0.08 to 0.20 0.11 (mean standard deviation); and (b) buildings with small roofs (primarily homes) constitute a large fraction of city roof area and have low albedos. These findings suggest that many commercial and residential buildings in California have roofs that could be made cooler (more reflective) to save energy. In addition, efforts to increase urban-scale albedo for heat island mitigation and climate change adaptation should include cool roof requirements for residential buildings where appropriate.

Speaker Biography

George Ban-Weiss, Ph.D., is an Assistant Professor in the Astani Department of Civil and Environmental Engineering at University of Southern California. Dr. Ban-Weiss' research group uses numerical models and field observations in concert to investigate local solutions for countering the impacts of climate change while reducing public exposure to air pollutants. In particular, his group uses field measurements to quantify the emissions source strength and atmospheric transformation of gas- and particle-phase pollutants, aerial measurements to characterize urban land cover, and numerical models and satellite observations to understand how changes in air pollutants and urban land use alter air quality and regional and global climate. Ban-Weiss received his B.S., M.S., and Ph.D. in Mechanical Engineering from the University of California, Berkeley. After graduate school he was a Postdoctoral Research Associate at the Carnegie Institution, Department of Global Ecology at Stanford. Prior to his current position, Ban-Weiss was a scientist at Lawrence Berkeley Laboratory. Dr. Ban-Weiss was recently named by MIT Technology Review as one of the world's 35 top innovators under the age of 35.

Ronnen Levinson, Ph.D., is a Staff Scientist and Leader of the Heat Island Group in the Energy Technologies Area of Lawrence Berkeley National Laboratory. Within his research portfolio he develops cool roof, wall, and pavement materials; improves methods for the measurement of solar reflectance; and quantifies the energy and environmental benefits of cool surfaces. Ronnen collaborates with researchers and regulators from the U.S., China, India, Brazil and Mexico to advance the appropriate use of cool materials in warm climates. He serves on the boards and technical committees of the Cool Roof Rating Council and the Global Cool Cities Alliance, and advises policymakers, code officials, utilities and building rating programs about cool surfaces. He holds a B.S. in engineering physics from Cornell University and an M.S. and a Ph.D. in mechanical engineering from the University of California at Berkeley. Dr. Levinson has authored or co-authored over 50 publications, and serves on the editorial boards of Energy & Buildings and Advances in Building Energy Research.

Jordan Woods has worked as a Research Assistant specializing in geospatial analysis. Projects Jordan Woods contributed to include the California Roof Albedo project, for the Lawrence Berkeley Heat Island Group, and the USGS Global Lake Mapping project, for the UCLA Geography Department. He received a B.S. in Environmental Science from the University of California, Berkeley in 2012.

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