Southern California is extremely dry, and that’s fueling fires − maps show just how dry

Ming Pan, University of California, San Diego, The Conversation on Jan 9, 2025

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Dry conditions across Southern California set the stage for a series of deadly wind-driven wildfires that burned thousands of homes in the Los Angeles area in early January 2025.

Ming Pan, a hydrologist at the University of California-San Diego’s Center for Western Weather and Water Extremes, tracks the state’s water supplies. He put Southern California’s dryness into perspective using charts and maps.

In early January, the soil moisture in much of Southern California was in the bottom 2% of historical records for that day in the region. That’s extremely low.

When the air is warm and dry, transpiration and evaporation suck water out of the plants and soil. Dry vegetation can provide fuel for flying embers to spread wildfires, as the Los Angeles area and the surrounding hills saw in early January.

Hydrologists in California watch the sky very closely every water year, starting in October. That’s 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. California relies on the Sierra snowpack for about one-third of its freshwater supply.

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 that hit the West Coast from October into January veered northward into Washington, Oregon and Northern California instead.

So, while Northern California’s water and snowpack conditions are in good shape, Southern California is not doing so well.

The Southern Sierra snowpack was starting to dip below normal in early January.

The U.S. Climate Prediction Center’s seasonal outlook through March suggests that drought is likely to develop in the region in the coming months. The outlook takes into account forecasts for La Niña, an ocean temperature pattern on its way to developing in the Pacific Ocean in early 2025, that 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.

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.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Ming Pan, University of California, San Diego

Ming Pan receives funding from the California Department of Water Resources and National Oceanic and Atmospheric Administration.