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103 In 2006 a notable heat wave spread throughout most of the United States and Canada, causing 140 fatalities in California.14 Probability of Future Extreme Heat Climate change is expected to generate an increase in ambient average air temperature, particularly in the summer. The outer Bay Area will likely experience greater temperature increases than coastal or bayside jurisdictions, though likely not as great as in the eastern-most inland communities. The frequency, intensity, and duration of extreme heat events and heat waves are also expected as regional climate impacts.15 According to California Climate Change Center, by mid-century, extreme heat in urban centers could cause two to three times more heat-related deaths than occur today.16 Statewide, temperatures could increase anywhere from 3 to 10.5 depending on CO2 emission levels, leading to more frequent, hotter days throughout the year. Extreme Heat Hazard in the Bay Area The Bay Area has historically experienced 4 extreme heat days a year.17 Depending on low and high emission scenarios, and the location within the region, in the future a city may experience an average of anywhere from 20 to 80 extreme heat days in a year. Cal-Adapt, California’s database of climate data and visualization tools provides five different ways to define the extreme heat hazard: (1) number of extreme heat days by year, (2) number of warm nights by year, (3) number of heat waves by year (heat wave is defined as 5 consecutive extreme heat days), (4) timing of extreme heat days by year (i.e. which months do extreme heat hazards occur), (5) the maximum duration of heat wave by year. These metrics are projecting both the intensity and the temporal nature of extreme heat. 14 Ibid 15 Drechsler D. M., et al, (2006) 16 California Climate Change Center (2006) 17 Cayan, D., et al. (2009) 142