Region San Francisco Bay Area


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.

Heat and Fire

The region is expected to warm by 3–4.5°F by 2050 and between 5.5–8°F by 2100. 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, increased fire risk. Maximum summer temperatures are also expected to increase by 3.6–7.4°F by midcentury, and as much as 9°F by the end of the century.

Rain and Snow

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.


The Bay Area will be severely impacted by sea-level rise and, when combined with high tides and storms, extreme flooding. By mid-century, the region is projected to see between 1.1–1.9 feet of sea-level rise by 2050, and between 3.4 feet and 6.9 feet by 2100, with the possibility of 10.2 feet under the extreme sea-level rise scenario.

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