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5.7.3.3 Urban Conflagration While the primary fire threat in the Bay Area is from wildfire, urban conflagration, or a large disastrous fire in an urban area, as a major hazard that can occur due to many causes such as wildfires, earthquakes, gas leaks, chemical explosions, or arson. The urban fire conflagration that followed the 1906 San Francisco Earthquake did more damage than the earthquake itself. A source of danger to cities throughout human history, urban conflagration has been reduced as a general source of risk to life and property through improvements in community design, construction materials, and fire protection systems. Although the frequency of urban conflagration fires has been reduced, they remain a risk to human safety. One reason is the current trend toward increased urban density and infill in areas adjacent to the wildland‐urban interface. In an effort to keep housing close to urban jobs, areas previously left as open space due to steep slopes and high wildland fire risk may be potentially considered as infill areas for high‐density housing. A memorable example of urban conflagration linked to wildland is the 1991 Oakland Hills firestorm. The firestorm occurred within a larger high fire hazard zone that is part of an approximately 60 mile stretch of hills running from the Carquinez Strait to San Jose in the eastern San Francisco Bay Area. The fire happened in an economically well‐off, largely built‐out residential area that has a long standing fire history linked to hot, dry fall winds and the presence of dense, flammable vegetation. 38 5.8 Drought A drought is a gradual phenomenon that occurs over several dry years, depleting reservoirs and groundwater basins without the expected annual recharge from winter precipitation. While drought does not have any primary impacts in the Bay Area, prolonged periods of drought can cause secondary impacts that can affect the region, including:  Reduced water supply for crops and livestock feed, impacting the economy centered around the agriculture industry  Increased wildfire hazard, including more fire starts and more prolonged conflagrations fueled by excessively dry vegetation and reduced water supply for firefighting purposes  Subsidence due to a lowering water table  May be correlated to high heat conditions. Drought is not localized, but occurs simultaneously across the region, and may extend statewide or across a larger expanse of western states. This has been the case in California since 2013. While the drought exists in every county, the impacts of the drought are locally 38 State of California Multi-Hazard Mitigation Plan, California Governor’s Office of Emergency Services