California’s droughts stem from a combination of natural climate patterns, rising temperatures that pull more moisture from soil and snowpack, and decades of water demand that consistently outpace supply. No single factor explains the state’s recurring water crises. Instead, several forces compound each other, turning dry spells that California has always experienced into emergencies that threaten farms, cities, and ecosystems.
High-Pressure Ridges That Block Rain
California gets most of its annual rainfall during a narrow winter window, when Pacific storms sweep inland from the ocean. When those storms are blocked, the entire year’s water budget can collapse. That’s exactly what happened during the winters of 2013-2014 and 2014-2015, when an enormous ridge of high pressure parked itself off the West Coast and refused to move. Meteorologists nicknamed it the “Ridiculously Resilient Ridge.”
This high-pressure zone acts like a wall in the atmosphere. Moisture-laden storms that would normally hit California get deflected north toward Alaska or south toward Baja, leaving the state warm and dry for months at a time. NOAA researchers found that these ridges are one phase of a natural circulation pattern in the upper atmosphere, meaning they aren’t directly caused by climate change. But when they do form, warmer background temperatures make their consequences far worse than they would have been decades ago.
Shrinking Snowpack, Shrinking Supply
The Sierra Nevada snowpack functions as California’s largest natural reservoir. Snow accumulates in the mountains through winter, then melts slowly through spring and summer, feeding rivers, filling reservoirs, and recharging groundwater. Two-thirds of the state’s surface water supply depends on this process.
That reservoir is disappearing. Between 1955 and 2020, the average April 1 snowpack across the Sierra Nevada declined by 19%, according to the Environmental Protection Agency. Looking ahead, the California Department of Water Resources projects a 48% to 65% loss from the historical April 1 average due to climate change. The problem isn’t only that less snow falls. Warmer temperatures cause snow to melt earlier and faster, meaning less water is available during the dry summer months when California needs it most. Some precipitation that would have fallen as snow now falls as rain, which runs off quickly instead of being stored on the mountainside for months.
Hotter Air Dries the Land Faster
Rising temperatures don’t just melt snowpack. They also increase the atmosphere’s ability to pull moisture out of soil, plants, and reservoirs through a mechanism called vapor pressure deficit. As air gets warmer, it can hold exponentially more moisture, but actual humidity isn’t rising nearly as fast. The gap between how much moisture the air can hold and how much it actually holds creates a powerful drying force.
This means that even when California receives normal rainfall, more of that water evaporates before it can soak into the ground or flow into streams. Plants lose water through their leaves faster, soils dry out more quickly, and vegetation becomes the kind of tinder that fuels catastrophic wildfires. In practical terms, the same amount of rain in 2024 produces less usable water than the same amount of rain in 1970, simply because the atmosphere is hungrier for moisture.
Groundwater Running on Borrowed Time
When surface water runs short, California turns to groundwater, and it has been pumping far more than nature can replace. In the southern Central Valley, the state’s largest farming region, groundwater overdraft runs nearly 2 million acre-feet per year. That’s more than 10% of the region’s total net water use being extracted from underground reserves that took centuries to accumulate.
This overdraft has visible consequences. Land in parts of the San Joaquin Valley has sunk by feet, permanently compressing the underground aquifers and reducing their capacity to store water in the future. Wells run dry. Neighboring communities lose access to drinking water. California passed the Sustainable Groundwater Management Act in 2014, requiring local agencies to form sustainability plans and eliminate overdraft within 20 years, but the timeline means many basins won’t reach balance until the mid-2030s or early 2040s. In the meantime, every drought year accelerates the drawdown.
Agriculture’s Enormous Water Footprint
Farms use roughly 80% of all water consumed by homes and businesses in California, or about 40% of the state’s total developed water supply (the rest goes to environmental flows for rivers and wetlands). That share reflects California’s role as the country’s top agricultural producer, growing everything from almonds to alfalfa in one of the world’s most productive farming regions.
Not all crops use water equally. Feed crops like alfalfa, pasture, and corn silage cover a quarter of irrigated acreage and consume 27% of farm water. Meanwhile, California has seen rapid growth in perennial fruit and nut crops, especially almonds. Unlike annual crops such as tomatoes or lettuce, almond trees can’t be fallowed during a dry year without killing the orchard, which represents years of investment. This locks in water demand regardless of supply conditions. Vegetables and berries generate high revenue per unit of water, but the sheer acreage devoted to feed and nut crops means agriculture’s total draw remains massive even during the worst droughts.
Weather Whiplash Makes Planning Harder
California’s climate is becoming more volatile, not just drier. The state swung from a record multi-year drought between 2012 and 2016 to extreme flooding during the 2016-2017 winter, a pattern scientists call weather whiplash. Climate modeling projects that these wild swings will intensify: the frequency of extreme flooding events comparable to California’s catastrophic Great Flood of 1862 could increase more than threefold over the course of this century. Dry extremes are also projected to increase, though by a smaller margin.
This volatility is its own kind of problem. Wet years sound like drought relief, but intense rainfall on parched, hardened soil causes flooding and erosion rather than slow absorption into aquifers. Reservoirs can only capture so much during a single storm season, and infrastructure designed for California’s historical climate isn’t built to handle rapid oscillation between bone-dry and record-wet conditions. The result is a paradox where the state can experience devastating floods and still not bank enough water to prevent the next drought.
Why Droughts Keep Getting Worse
California has always been a dry state prone to periodic drought. Tree ring records show megadroughts lasting decades long before European settlement. What has changed is the context surrounding those dry spells. A warmer atmosphere dries the land faster and melts snowpack earlier. Forty million people and a $50 billion agricultural industry demand water at a scale that didn’t exist a century ago. Groundwater reserves that once served as a buffer have been drawn down to unsustainable levels.
Each of these factors feeds the others. Less snowpack means more groundwater pumping, which means less stored water for the next drought. Higher temperatures mean drier soil, which means more irrigation, which means more demand on an already strained system. California’s droughts aren’t caused by any single villain. They emerge from a collision between a naturally variable climate, a warming atmosphere, and a water system built on the assumption that 20th-century conditions would last forever.