California Air Resources Board

SACRAMENTO - California can expect more frequent and more dangerous heat waves in the coming decades, the result of global warming and the state’s aging population, according to a new climate-modeling study commissioned by the California Air Resources Board.

Researchers using a new, more comprehensive weather-modeling method found that the incidence of prolonged hot spells – those lasting 10 or more days – could rise by a factor of two to ten by the 2090s, depending on the region.

“Along with reducing our climate-warming emissions, we need to prepare for longer and hotter heat waves,” Board Chairman Mary Nichols said. “Raising public awareness of the risks and having safety nets such as community cooling centers can greatly reduce those risks.

Currently, an average of about 500 elderly people die from excessive heat each year in the nine major urban areas studied: Fresno, Los Angeles, Oakland, Santa Ana, Riverside, Sacramento, San Diego, San Francisco and San Jose. By the 2090s, the death toll within this population group could rise more than nine-fold – to a range of roughly 4,700 to 8,800 – depending on the climate scenario, according to the study.

A warmer climate plays a role, but as much as 75 percent of the projected increase in potential heat-related mortality is attributed to demographics. The elderly are particularly vulnerable to extreme heat, and the proportion of Californians 65 and older is expected to continue growing at unprecedented rates well into the 21st century.

Scott Sheridan, a Kent State University geographer who led the study, said the analysis is the first to include demographic factors in predicting changes in California’s heat-related deaths. Also, the projections are based on stronger climate modeling techniques than those he used in a 2006 preliminary analysis for the ARB. The latest model, for example, accounts for a fuller suite of weather conditions that affect how the human body responds to heat -- cloud cover, dew point, wind speed, among other variables – making it a better predictor of potential heat-related deaths.

The researchers recommend that California take preventative actions, such as setting up extreme heat warning system at weather forecast stations statewide and a heat-health task force in every major city to coordinate and update safety plans.

The study is available at: http://www.arb.ca.gov/newsrel/2011/HeatImpa.pdf