ARB Research Seminar

This page updated June 19, 2013

Cooling Summer Daytime Temperatures in Coastal California During 1948-2005 : Observations, Modeling and Implications

Robert Bornstein, Ph.D., Department of Meteorology, San Jose State University, Jorge Gonzalez, Ph.D., and Bereket Lebassi, Department of Mechanical Engineering, Santa Clara University, and Haider Taha, Ph.D., Altostratus Inc.

August 19, 2008
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA



The study evaluated long-term (1948-2005) air temperatures in California during summer (June-August). The aggregate results showed asymmetric warming, as daily minimum temperatures increased faster than daily maximum temperatures. However, the spatial distributions of daily maximum temperatures in the South Coast (Southern California) and San Francisco Bay Area air basins exhibited a complex pattern, with cooling at low-elevation coastal areas and warming at inland areas.

Previous studies have suggested that cooling summertime maximum temperatures in coastal California were due to increased irrigation, coastal upwelling, or cloud cover. However, a current hypothesis is that this temperature pattern arises from a "reverse-reaction" to green house gas (GHG) induced global warming. In this hypothesis, the global warming of inland areas results in increased sea breeze activity in coastal areas. Average temperatures from global circulation models (GCM) show warming that decreases from inland areas of California to its coastal areas.

However, such large scale models cannot resolve these smaller scale topographic and coastal effects. Meso-scale modelling on a 4 km grid is thus being carried out to evaluate the contributions from GHG global warming and land use changes (including urban heat island development) to the observed trends. Significant societal impacts may result from this observed reverse reaction to GHG warming, and possible beneficial effects include decreased: maximum O3 levels, human thermal-stress, and energy requirements for cooling.

While Professor Bornstein will make the presentation, the study collaborators, Drs. Taha, Gonzalez, and Lebassi will also be available to respond to questions and comments.

Speaker Biography

Robert Bornstein, Ph.D., has served at the Department of Meteorology at San Jose State University since 1969. Professor Bornstein's research has included modeling and observation of how urbanization creates new urban climates and how these new climates control the spread of air pollution within urban environments. Professor Bornstein was elected American Meteorological Society Fellow in 2004 and was editor of "Atmospheric Environment." Professor Bornstein is currently on the Bay Area Air Quality Management District Technical Advisory Committee and on the World Meteorological Organization's Committee on Urban Climate. Professor Bornstein's 3-D urban modeling efforts include MM5 simulations of meteorological conditions during the maximum SCOS97 ozone episode, as well as similar studies for Houston, New York City, Atlanta, and Israel.

Haider Taha, Ph.D., is an atmospheric modeler with over 17 years of experience in meteorological, emission, and photochemical air quality modeling. Dr. Taha has extensive experience in urban meteorological modeling and urban heat island (UHI) mitigation for a wide variety of California cities (for the California Energy Commission), Houston, and New York City. From 1990 to 2003, Dr. Taha was a staff scientist with Lawrence Berkeley National Laboratory. In addition to establishing and serving as President of Altostratus Inc. in 2003, Dr. Taha is Adjunct Professor of Meteorology at San Jose State University.

Jorge Gonzalez, Ph.D., is is a professor in the Department of Mechanical Engineering at Santa Clara University (SCU). Dr. Gonzalez is a heat and mass transfer computational modeler and experimentalist. Dr. Gonzalez has applied computational and analysis techniques to regional atmospheric and climate processes in coastal areas, particularly in the Caribbean and Central California. Dr. Gonzalez has enhanced meso-meteorological models with cloud microphysics schemes and coupled them to General Circulation Models. Dr. Gonzalez has also coordinated city-scale and island-scale experimental campaigns, including detection of UHIs.

Bereket Lebassi is a Ph.D. candidate at the Department of Mechanical Engineering at Santa Clara University (SCU). He received his M.S. degree at San Jose State University, with a thesis on the simulation of sea breeze flows in the Monterey Bay area. His doctoral research at SCU has included analyses and simulation of temperature trends in California, as well as their impacts on electrical-energy loads.

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