Wednesday October 1, 2025
ABC 10 —
SACRAMENTO, Calif. — The 2024-25 California Water Year closed September 30 with near average precipitation but there was a marked difference between the northern and southern parts of the state. North of I-80 trended wetter than average, whereas south of I-80 was drier than average. Overall though the state reached nearly 100% of its annual snowpack and the largest reservoirs stayed above average.
This all follows two fairly wet years, with the biggest one being 2022-23, which helped dig the state out of growing drought.
California State Climatologist, Dr. Michael Anderson, said in terms of this past water year, much of the coast maintained near average to slightly above average temperatures, but the valley and mountains were on average much warmer.
The warm temperatures are concerning, especially when considering that although we reached near-average snowpack, it melted off quicker than average.
As we begin the new water year on October 1, Anderson said it’s worth noting the potential of La Niña conditions with cooler-than-average water temperatures in the tropical Pacific. He added that there is much warmer than average water, though, in the northern Pacific, which could alter the storm track moving into the wet season.
Karla Nemeth, Director of the California Department of Water Resources, says one of the biggest challenges moving forward is the wild swings within the wet season, going back and forth from extreme wet events to dry ones. She says climatologically this trend looks very likely to continue with more climate induced weather events like floods and devastating wildfires like what the state saw in early January 2025.
This highlights the need for conservation, improved forecasts, and adaptation for storage opportunities.
Water is a key natural resource that helps shape California. Too much water can result in catastrophic flooding, but too little can push the state into drought. Measuring and storing this vital resource helps the economy, agriculture and the population thrive.
California’s Water Year runs from October 1 through September 30 the following year. During that time, managers are carefully calculating what is too much and what is not enough. The state’s storage and conveyance system is one of the most elaborate in the world marked by two distinct periods of a wet and a dry season.
Nearly 50% of California’s annual rainfall comes in three short months: December, January and February. These can be make or break months for yearly water supply in the state. The absence of storms during this period can send the state into drought.
This is also a period of peak snowfall another vital part of California’s water supply. In fact, snowpack and subsequent snow melt accounts for nearly 1/3 of California’s water supply. Snow melts filling downstream reservoirs which can then be giant containers of water for the dry season. The beauty of this is how it all works in conjunction with nature. Snowpack peaks typically on April 1 right about the time the state is starting to enter its dry season.
California’s year-to-year precipitation variability makes this especially complicated. In fact, no other state in the country has the consistent extreme swings from dry to wet years.
Three important projects were set up to store and import much of the water used by the state:
- Central Valley Project (CVP) – this was built by the federal government. The largest reservoir is Lake Shasta which sits at the headwater of the Sacramento River in the north end of the Sacramento Valley. Water from this reservoir is sent as far south as Bakersfield in the southern end of the San Joaquin Valley.
- State Water Project (SWP) – this was built by California. The largest reservoir is Lake Oroville which sits at the headwater of the Feather River. The California Department of Water Resources says water is moved through dams, reservoirs, power plants, pumping plants and aqueducts to serve over 27 million people and 750 million acres of farmland.
- Colorado River – water from the Colorado River is moved through the Colorado Aqueduct to Southern California. This water is the main drinking water source for people served by the Metropolitan Water District of Southern California (MWD).
One of the newer frontiers which is quickly becoming another storage resource in the state is groundwater, which is naturally stored beneath the surface. Largely unmanaged until recently, this is now the focus of more regulation.
Going back to Dr. Anderson’s comments on La Niña conditions developing. There is a 71% chance of La Niña October through December 2025. This is the phase of the El Niño/Southern Oscillation (ENSO) when cooler than average waters in the Niño 3.4 region can have global impacts. La Niña tends to not be a key predictor though in California’s wet season with nearly an equal chance of wet or dry conditions. Anderson points out one of the key signatures of La Niña pattern in the Western U.S. though is the presence of cooler than average temperatures. Where that cold pool settles, can be a make or break for the Sierra snowpack and even the potential of off-shore wind events which can bring extreme fire conditions.
The Climate Prediction Center is favoring a La Niña type of pattern for California during the wettest months of the year. This would highlight below average precipitation in Southern California with an equal chance of above or below precipitation in Northern California. The temperature outlook calls for above normal condition in Southern California with an equal chance of above or below average conditions in Northern California.