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Last Edited: 4/15/2014

Health Impacts from the 2006 California Heat Wave

CEHTP collaborated with the Natural Resources Defense Council to conduct an analysis of the 2006 heat wave in California.  The results showed that, during the heat wave, there were 1,182 more hospitalizations and 16,166 more emergency room visits than would be expected.  This research is essential for better understanding and planning for future heat events in California.



Climate models project that heat waves will increase in frequency and severity.  Despite many studies of mortality from heat waves, few studies have examined morbidity.  Age and race/ethnicity groups were investigated to determine if any groups experienced increased hospitalizations and emergency department (ED) visits during the 2006 California heat wave.



County-level hospitalizations and ED visits for all causes and for 10 cause groups were aggregated into six geographic regions of California.  Excess morbidity and rate ratios (RRs) were calculated during the heat wave (July 15–August 1) and compared to data from a reference period (July 8–14 and August 12–22).



During the heat wave, 16,166 excess ED visits and 1,182 excess hospitalizations occurred statewide.  ED visits for heat-related causes increased across the state, especially in the Central Coast region, including San Francisco.  Children (0–4 years of age) and the elderly (65 years of age or older) were at greatest risk.  Overall, the 2006 California heat wave had a substantial effect on morbidity, including in regions with relatively modest temperatures.  This suggests that existing population acclimatization and adaptive capacity influenced risk.  By better understanding these impacts and population vulnerabilities, local communities can improve their emergency preparedness and heat warning systems to better cope with future heat events. View complete results in the full report.



  • Columbia University, Mailman School of Public Health
  • Natural Resources Defense Council
  • University of California, San Francisco



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