Global warming is making flooding in California more likely and more severe. Floods can happen from overflowing rivers, coastal storm surge, or heavy rain that overwhelms urban drainage systems.
California's climate is becoming more unstable, causing bigger swings between very dry and very wet periods—often called “weather whiplash." Even if the total amount of rain and snow doesn't change, the pattern is becoming more extreme. As temperatures rise, more rain falls instead of snow, and the snow that does fall melts faster. This reduces our snowpack, affects our water supply, and increases flood risk. Sea level rise and unstable land after wildfires also add to flooding dangers.
A major driver of year‑to‑year rainfall change is atmospheric rivers—large bands of heavy water vapor in the sky. Storms with atmospheric rivers provide half of California's rain and cause its biggest and most expensive floods.
See below for more on health impacts from floodng, what to expect from El Niño and La Niña, and additional flooding resources.