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<br /> <br />most inland communities. The frequency, intensity, and duration of extreme heat events <br />and heat waves are also expected as regional climate impacts.49 <br />According to California Climate Change Center, by mid-century, extreme heat in urban <br />centers could cause two to three times more heat-related deaths than occur today.50 <br />Statewide, temperatures could increase anywhere from 3 to 10.5 depending on CO2 <br />emission levels, leading to more frequent, hotter days throughout the year. <br />5.9.3 Extreme Heat Hazard in the Bay Area <br />The Bay Area has historically experienced 4 extreme heat days a year.51 Depending on low <br />and high emission scenarios, and the location within the region, in the future a city may <br />experience an average of anywhere from 20 to 80 extreme heat days in a year. Cal-Adapt, <br />California’s database of climate data and visualization tools provides five different ways to <br />define the extreme heat hazard: (1) number of extreme heat days by year, (2) number of <br />warm nights by year, (3) number of heat waves by year (heat wave is defined as 5 <br />consecutive extreme heat days), (4) timing of extreme heat days by year (i.e. which months <br />do extreme heat hazards occur), (5) the maximum duration of heat wave by year. These <br />metrics are projecting both the intensity and the temporal nature of extreme heat. <br />Intensity <br />The intensity of extreme heat is defined differently for each location in the region. In San <br />Francisco County an extreme heat day is defined as a day above 78, while for inland <br />portions of Solano County extreme heat is defined as a day above 100. The threshold is <br />the 98th percentile historic maximum temperature. The threshold is set locally to recognize <br />services and buildings in cooler climates may not be designed to handle moderate heat, <br />while those areas where high heat has always been an occurrence, already have measures <br />to address their historic temperatures. <br />In addition to the number of extreme heat days expected to rise in the Bay Area, the <br />temperature is expected to increase well above thresholds over the next century. In San <br />Francisco County by the end of the century there could be multiple days a year where <br />temperatures reach 95, while in Solano County there may be multiple days above 115 <br />each year. <br />5.9.3.1 Temporal <br />Extreme heat is made worse when it is experienced over a longer stretch of time. The <br />number of heat waves (five or more consecutive days of extreme heat) will increase as will <br /> <br />49 Drechsler D. M., et al, (2006) <br />50 California Climate Change Center (2006) <br />51 Cayan, D., et al. (2009)