“Mid-Century Warming in the Los Angeles Region” is the first study to provide specific climate change predictions for the greater L.A. area, with unique predictions down to the neighborhood level. The report, the most sophisticated regional climate study ever developed, was produced by UCLA with funding and support from the City of Los Angeles, in partnership with the Los Angeles Regional Collaborative for Climate Action and Sustainability (LARC). It is available online at c-change.la.

The report, led by UCLA Prof. Alex Hall (Dept. of Atmospheric and Oceanic Sciences), shows that climate change will cause temperatures in the Los Angeles region to rise by an average of 4-5 degrees by midcentury, tripling the number of extremely hot days in downtown L.A., and quadrupling them in the valleys and at high elevations.

Visit c-change.LA to learn more and find out how Greater L.A. can adapt.

The unprecedented coalition of cities, universities, businesses, non-profits and other agencies in the LARC made the study possible. Mayor Antonio Villaraigosa and the City of Los Angeles led the way, obtaining Department of Energy grant from the federal stimulus to study and share climate research. Though scientists knew to expect warming, this is the first time policy makers in the L.A. area have precise information to base plans on.

The study looked at the years 2041-2060 to predict the average temperature change by mid-century. The data covers all of Los Angeles County, and 30-60 miles beyond, including all of Orange County, parts of Ventura, San Bernardino and Riverside counties, and reaching as far as Palm Springs, Bakersfield and Santa Barbara. The study overlaid the area with a grid of squares 2km (1.2 miles) across, with unique temperature predictions for each square, unlike global climate models, which normally use grids 60-120 miles across – big enough to include regions as different as Long Beach and Lancaster.

According to the study, coastal areas like Santa Monica and Long Beach are likely to warm an average of 3-4 degrees Fahrenheit. Dense urban areas like downtown L.A and the San Fernando and San Gabriel valleys will warm an average of 4 degrees, and mountain and desert regions like Palm Springs and Lancaster will warm 4-5 degrees.

These figures are only annual averages, and the day-to-day increase in temperatures will vary. Southern Californians should expect slightly warmer winters and springs, but much warmer summers and falls, with more frequent heat waves. Temperatures now seen only on the seven hottest days of the year in each region will happen two to six times as often. The number of days when the temperature will climb over 95 degrees will increase two to four times, depending on the location. Those days will roughly double on the coast, triple in downtown Los Angeles and Pasadena, quadruple in Woodland Hills, and climb from an average of 75 days annually in Palm Springs to roughly 120 days.

Other cities and states have localized global climate models, but usually by localizing only one model. Hall’s team needed months of computer time to downscale 19 global climate models, each with slightly different assumptions about how to predict climate change or factors like future greenhouse gas emissions. Once UCLA recalculated the almost two dozen global models at the local level, the results were analyzed and integrated into an ensemble projections to create the climate model for the region.

“Mid-Century Warming in the Los Angeles Region” is the first of five planned studies Hall will conduct for the city and the LARC about how climate change will affect the Southland. Hall’s team is performing similarly comprehensive models for local rainfall, Santa Ana wind patterns, coastal fog (including June gloom), and soil moisture, run-off and evaporation.

The complete study, “Mid-Century Warming in the Los Angeles Region,” along with interactive maps and ways to get involved, is available online at c-change.la.

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View the Los Angeles Times article on this study as well.

Published: Thursday, June 21, 2012