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Background
The San Francisco Bay Area region includes San Francisco, Marin, Contra Costa, Alameda, Santa Clara, San Mateo, Sonoma, Napa, and the western half of Solano counties. Its Mediterranean-type climate, characterized by mild, wet winters and warm, dry summers, supports high biological diversity. The Bay Area is well known as the home of a thriving technology industry, wine and dairy industries, as well as a robust recreation industry bolstered by the region’s rivers and both bay and coastal waterfronts. The region has over 100 cities and towns with a total population of over 7 million residents.
Extreme Heat, Drought, and Wildfire
The region is expected to warm by 3.3–4.4°F by 2050 and between 4.2–7.2°F by 2100. Maximum summer temperatures are expected to increase more drastically by end of century, by 3.9–6.3°F near the coast and 6.4–10°F further inland. Warming average temperatures, regardless of total precipitation level changes, will cause droughts to become longer and more severe and, coupled with development in the wildland-urban interface, will lead to increased fire risk.
Flood
Current year-to-year variability in precipitation is expected to continue, with fluctuation between very wet and very dry years. Approximately 60% of the region’s water supply is sourced in the Sierra Nevada and Sierra snowmelt provides 40% of the annual water to the San Francisco Bay Delta, which is expected to be impacted by warming temperatures and changes in precipitation. The Bay Area region’s characteristic wet winter will bring more intense and damaging winter storms, and, as surface temperatures continue to rise, the historic location of the freezing line in mountains will move upslope, causing more storms to fall as rain rather than snow.
Sea Level Rise
The Bay Area will be severely impacted by sea level rise and, when combined with high tides and storms, extreme flooding. Sea level is projected to rise by between 1.6 feet and 3.1 feet by 2100, with slim potential for a rise as high as 6.5 feet.