University of California scientists announced on Mar. 9 that increasingly intense and frequent rainstorms in the San Francisco Bay Area are raising flood risks, especially for homeless people living near rivers and streams. Researchers say these weather changes threaten some of the region’s most vulnerable residents, highlighting the need for targeted planning and intervention.
The study matters because it identifies areas where people with limited resources face heightened danger from flooding, helping cities prepare and protect those at greatest risk. Using data from the Centers for Disease Control’s Social Vulnerability Index, researchers mapped out which census tracts in the Bay Area are most exposed to storm-related hazards due to factors like low income, housing instability, and minority status.
“Windy rainstorms will become rainier as the climate warms, which means that flood risks will increase,” said Igor Lacan, UC Cooperative Extension environmental horticulture and urban forestry advisor for the Bay Area. “This is a concern for homeless people living in or near urban stream corridors.” Gregory Pasternack, a professor at UC Davis who worked on the study with Lacan and hydroclimatologist Nikhil Kumar, said: “As people work on planning for climate change, they should take into consideration the people and places that are most vulnerable, who have the least ability to cope with extreme storms. People living unsheltered are those most vulnerable.”
Maps created by the team show that while all areas need preparation, certain locations—marked in red—require special attention due to overlapping social vulnerability and high storm frequency. These include both urban sites like San Jose and Hayward as well as inland communities such as Concord, Santa Rosa, Vallejo, Antioch, Richmond, and Oakland. Pasternack said: “While some people are working hard to find homes for folks in encampments, meanwhile the number of people losing their housing is still growing… Therefore we need to take steps to provide support for people where they are.”
Daniel Swain of UC Agriculture and Natural Resources (UC ANR), who was not involved in this study but researches extreme weather trends in California, said: “The heaviest downpours in a warming California will become even more intense… that’s likely going to increase the risk of flooding in urban areas and along creeks… Knowing in advance which areas have an especially high overlap between storm-related inundation risk and highly vulnerable populations can help pinpoint where targeted interventions are most needed.”
Lacan, Kumar and Pasternack have published fact sheets with maps showing vulnerable areas along with tips for protecting residents. These resources can be downloaded from Lacan’s website or requested via email from Pasternack.
To address these challenges long-term, researchers recommend timely flood alerts; investing in storm drain maintenance; prioritizing relocation efforts before major storms; and adapting water management systems to handle increased rainfall rates.
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