Southern California is extremely dry, and that’s fueling fires − maps show just how dry
- Written by Ming Pan, Senior Research Hydrologist, University of California, San Diego
Dry conditions across Southern California set the stage for a series of deadly wind-driven wildfires that burned thousands of homes and other structures[1] in the Los Angeles area in early January 2025.
Ming Pan[2], a hydrologist at the University of California-San Diego’s Center for Western Weather and Water Extremes[3], tracks the state’s water supplies. He put Southern California’s dryness into perspective using charts and maps.
How dry is Southern California right now?
In early January, the soil moisture in much of Southern California was in the bottom 2% of historical records[4] for that day in the region. That’s extremely low.
Hydrologists in California watch the sky very closely starting in October[6], when California’s water year begins.
The state gets very little rain from May through September, so late fall and winter are crucial to fill reservoirs and to build up the snowpack to provide water. California relies on the Sierra snowpack for about one-third of its freshwater supply[7].
However, Southern California started out the 2024-25 water year pretty dry. The region got some rain from an atmospheric river in November, but not much. After that, most of the atmospheric rivers[8] that hit the West Coast from October into January veered northward into Washington, Oregon and Northern California instead.
When the air is warm and dry, transpiration[9] and evaporation also suck water out of the plants and soil. That leaves dry vegetation that can provide fuel for flying embers to spread wildfires[10], as the Los Angeles area saw in early January.
Water year data from Oct. 1, 2024, to Jan. 7, 2025, shows precipitation levels and the anomaly from the 1991-2020 average.
Center for Western Weather and Water Extremes[11]
So, while Northern California’s water and snowpack conditions[12] are in good shape, Southern California is much drier and its water storage is not doing so well.
The Southern Sierra snowpack was starting to dip below normal in early January.
How snowpack and reservoir levels as of Jan. 7, 2025, compare with the 2000-2015 average in Northern and Southern California. The shaded areas show normal reservoir levels (blue) and reservoir levels plus snowpack (gray). The lines track each for the 2025 water year.
Center for Western Weather and Water Extremes[13]
What can California expect for the rest of 2025?
The U.S. Climate Prediction Center’s seasonal outlook through March suggests that drought is likely to develop[14] in the region in the coming months.
The outlook takes into account forecasts for La Niña[15], an ocean temperature pattern that was on its way to developing in the Pacific Ocean in early 2025. La Niña tends to mean drier conditions in Southern California. However, not every La Niña affects California in the same way.
One or two big rain events could completely turn the table for Southern California’s water situation. In 2023, California saw atmospheric rivers in April[16].
So, it’s hard to say this early in the season how dry Southern California will be in the coming months, but it’s clear that people in dry areas need to pay attention to the risks.
References
- ^ burned thousands of homes and other structures (apnews.com)
- ^ Ming Pan (scholar.google.nl)
- ^ Center for Western Weather and Water Extremes (cw3e.ucsd.edu)
- ^ in the bottom 2% of historical records (www.drought.gov)
- ^ NASA (www.drought.gov)
- ^ starting in October (cw3e.ucsd.edu)
- ^ the Sierra snowpack for about one-third of its freshwater supply (water.ca.gov)
- ^ atmospheric rivers (theconversation.com)
- ^ transpiration (www.usgs.gov)
- ^ flying embers to spread wildfires (apnews.com)
- ^ Center for Western Weather and Water Extremes (cw3e.ucsd.edu)
- ^ snowpack conditions (water.ca.gov)
- ^ Center for Western Weather and Water Extremes (cw3e.ucsd.edu)
- ^ drought is likely to develop (www.cpc.ncep.noaa.gov)
- ^ takes into account forecasts for La Niña (www.cpc.ncep.noaa.gov)
- ^ atmospheric rivers in April (theconversation.com)
Authors: Ming Pan, Senior Research Hydrologist, University of California, San Diego
