New research warns of major threats to Sacramento’s water supply
Warming temperatures and shifting precipitation patterns will reshape the American, Bear and Cosumnes river watersheds, intensifying snowpack loss and placing greater strain on California’s water supply, a two-year study has found.
A draft watershed resilience report by the Regional Water Authority reviewed by The Sacramento Bee projects earlier snowmelt, shifting runoff patterns, and more water lost to evaporation due to climate change.
The report, expected to be released by the end of March, noted an average of 6.3 degrees of warming by the end of the century compared with temperatures from 1981 and 2010, with the Sierra region expected to warm even faster, and the American River area projected to face an average of 39 additional extreme heat days each year.
It also predicts snow water equivalent measurement at 7.2 inches on average — a 66% decrease compared with historical data — by the mid‑century period, between 2041 and 2070, and 4.6 inches — a 79% decrease — by the end of the century for the American River region.
“We could have the same amount of water coming, but we’re going to have less water supply because we have infrastructure that has to be focused on addressing flood risks when the water is coming, instead of water supply,” said Ryan Ojakian, government relations manager at the Regional Water Authority.
The crux of the problem lies in how California’s water system was created for an old climate. Reservoirs were designed to collect snowmelt that gradually trickled down from the mountains through spring and early summer, providing a steady water supply long after the rainy season.
But now, warmer winters cause snow to melt earlier and storms to deliver more rain than snow, so much of that water arrives in short, powerful bursts. Because reservoir operators must keep a portion of reservoir space empty to reduce flood risk during major storms, this poorly timed influx of water could force releases instead of storage, leaving less water available later in the year.
Historically, peak runoff occurred around May, but the study predicts it will move to roughly March by the end of the century. As more water arrives in winter rather than being spread across the spring months, the system would no longer work as intended — and without new ways to capture that water, much of it would be lost, Ojakian said.
“We’re going to have this increased threat of reduced water supply. The alternative is, we could live at a higher risk of flooding, which we don’t want to do.”
From less snow to bigger storms
A common misconception about climate change, RWA officials said, is that it’s only reflected in hot, dry conditions. In reality, climate change amplifies both extremes, making wet seasons wetter and hot seasons hotter, and drives more intense, frequent, and unpredictable weather events.
In other words, the impacts of climate change are showing up not only in declining snowpack, but also in surges of flood events, and sharper swings between wet and dry conditions.
The draft showed that, compared with historical data, average extreme precipitation for the region is projected to increase by 15% in the mid‑century period and by 18% by the end of the century. Floods that last three days are expected to get bigger, about 11% higher on average between 2016 and 2065, and about 20% higher between 2051 and 2100.
Northern California saw several days of heavy storms earlier this month, pushing water supplies beyond full capacity. But snowpack water across the region remains below average, at 61% of the seasonal average and just 28% of the April 1 average as of Wednesday.
Jim Peifer, executive director at the Regional Water Authority, emphasized the analysis isn’t about a single event but averages over time, showing the projected impacts of climate change over decades.
“We can adapt to climate change, but it’s going to take appropriate investment to make sure that we have a livable community,” Peifer added.
The study also found that rising temperatures and declining runoff will increase the risk of severe droughts, with average drought probability rising 4% between 2016 and 2065 and 5% by the end of the century, compared with 1961 to 2010. As conditions dry, the region’s wildfire risk is also expected to rise, with the average probability of wildfires reaching 32% by the end of the century compared with late 20th- and early 21st-century data.
Storing more water underground
The local water officials urged a push to better manage groundwater, arguing it is one of the most practical ways to safeguard the region’s future water supply.
RWA officials said that during wet winters, agencies can rely more on river water and reduce groundwater pumping, giving aquifers a chance to refill instead of being constantly drained.
They also highlighted two tools to boost groundwater recharge — one is spreading extra river water onto special fields or basins, allowing it to soak into the soil and replenish the aquifer. The other is using aquifer storage and recovery wells, which can both pump groundwater out and inject surface water back in, effectively turning underground basins into a savings account for drier periods.
“My biggest fear is that we’re not ready for whatever that is, being a flood event, a drought event, a wildfire event,” Ojakian said.
“Because the shame is, if we weren’t sitting here today, we know that we could have been ready for that event, and that investment today will be far less expensive than we’re building from that event if we didn’t make those investments prior to it occurring.”
This story was originally published January 14, 2026 at 3:14 PM.
