If El Niño Brings Heavy Rain, Is California Ready to Capture and Store It?

California may be headed into a very wet winter. The more interesting question is whether we are ready to make the most of it.

In August, the National Oceanic and Atmospheric Administration (NOAA) reported a greater than 90% chance of a strong El Niño developing during the fall and winter of 2026–27. NOAA also estimated a 69% chance that the October through December period could produce an El Niño event among the strongest recorded since 1950. That sounds like good news for a state that is almost always worried about water, and it could be. But El Niño changes the odds; it does not dictate the weather. Even strong El Niño events can produce very different results in California. Some have brought extraordinary amounts of rain, while others fell short of expectations.

So, if the storms come this winter, can California capture the water? The answer is more complicated than simply asking how much room is left in our reservoirs. California has made real progress in preparing for wetter and more unpredictable conditions. But capturing water depends on a combination of storage capacity, weather forecasting, infrastructure, water rights and environmental requirements. In many cases, the opportunity to capture water may last only a few days.

Having Room in A Reservoir Does Not Mean We Can Fill It

California has a vast network of reservoirs, but an empty space in a reservoir does not necessarily mean it’s available for water storage. Reservoirs have several jobs. They store water for cities, farms and businesses, but they also help protect communities from flooding and must be operated in ways that account for downstream conditions, fish and wildlife, and other water-management requirements.

Consider what happens when a major storm is forecast. If a reservoir already holds a significant amount of water, the operator may need to release some of it before the storm arrives, creating room for expected storm runoff. Releasing too much water can be a problem if the storm produces less rain than expected. Holding too much water can be a problem if the storm is larger than expected and the reservoir does not have enough room to absorb the runoff. California’s storms are not always easy to predict: an atmospheric river can deliver enormous amounts of rain in a matter of days, but its location, intensity and timing can change.

That is why storage capacity and the ability to capture water are not the same thing. California needs reservoirs with room to hold water, but it also needs the ability to make good decisions about when to release water and when to keep it.

The timing problem is becoming more important as California’s climate changes. For decades, the Sierra Nevada snowpack acted as a natural reservoir, accumulating during the winter and gradually melting during the spring and summer. As temperatures rise, California receives more precipitation as rain rather than snow, and snow is melting earlier. That can mean more runoff arriving during winter storms and less water being stored naturally in the mountains for later in the year.

The challenge, then, is not simply to capture more water. It is to capture water at the right time without increasing flood risk or giving up water that California will need later.

Water Flowing Down A River Is Not Automatically Available to Divert

There is another part of the story that is less visible but just as important: the law. When a major storm sends water rushing down a California river, we assume that someone can capture it. But California’s water-right system determines who can divert surface water, when it can be diverted and under what conditions.

Generally, a new diversion requires a water right. The State Water Resources Control Board considers whether water is available for appropriation and whether a proposed diversion could interfere with someone’s existing water rights or other beneficial uses. That means a river can carry an enormous amount of water without the water being legally available for someone else to take.

California has created several tools to make it easier to take advantage of short periods of high flows, particularly for groundwater recharge. Groundwater recharge is essentially the underground version of putting water in a reservoir. During wet periods, agencies can divert to recharge basins, agricultural land or other suitable areas and allowing it to soak into the ground, replenishing groundwater supplies that remain available for future use.

The State Water Board currently offers temporary permits for certain groundwater recharge projects lasting either 180 days or five years. The five-year permits are particularly useful because they can allow qualifying agencies to recharge water during five successive wet seasons rather than starting the permitting process again each year. California has also created a special pathway for certain floodwater recharge projects. Water Code section 1242.1 allows qualifying parties to divert certain floodflows for groundwater recharge without an appropriative water right during the statutory period ending January 1, 2029. But the statute comes with specific requirements involving flood risk, existing water rights, fish protection, diversion facilities, reporting and other conditions. It is an important opportunity, but it is not a blanket exemption from California’s water-right laws.

But obtaining the legal authority to divert water is only the first step. The project needs infrastructure to move and store the water, a groundwater basin that can absorb it, and approvals addressing water quality, groundwater sustainability, CEQA, and impacts on fish, wildlife, and other resources. That is why preparation matters. When a flood lasts only a few days, California needs to know in advance whether it can legally divert the water and it can put it.

Environmental Requirements Are Part of the Equation

Environmental rules governing water diversions are sometimes portrayed as obstacles to capturing more water, but the reality is more nuanced. California’s rivers, streams, and Delta support fish and wildlife, provide drinking and irrigation water, and serve many other beneficial uses. As a result, the State Water Board’s groundwater-recharge programs require consideration of existing water rights, water availability, CEQA, public-trust resources, and impacts on fish and wildlife. The flood-recharge program similarly includes protections for aquatic resources. These requirements do not mean California cannot capture stormwater; they mean the amount it can capture depends on where the water is, when it arrives, and how diversion could affect other resources and legal rights.

The Delta illustrates the challenge particularly well. During a major storm, enormous amounts of water may move through the Sacramento River system and into the Delta, but the State Water Project cannot simply pump all of it south. Delta operations must comply with water-rights requirements, water-quality standards, fishery protections, and other environmental and operational rules. Capturing more water therefore requires identifying opportunities that work within those constraints rather than treating every high-flow event as an unlimited supply.

Better Forecasts Could Help California Get More from Existing Reservoirs

California is also looking for ways to get more from the reservoirs it already has. Forecast-Informed Reservoir Operations, or FIRO, combines improved weather forecasts and hydrologic modeling with reservoir operations to help managers respond more precisely to approaching storms. With better information about a storm’s timing and intensity, operators may be able to release water in advance, creating space for incoming runoff while still retaining water when forecasts indicate it is safe to do so. The goal is to reduce flood risk without unnecessarily releasing water that California could otherwise store.

FIRO is already being successfully implemented at Lake Mendocino and is being incorporated into operations at Prado Dam. A 2025 assessment of Lake Oroville and New Bullards Bar Reservoir also found that FIRO could reduce flood risk and provide potential water-supply benefits at those facilities.

New Bullards Bar offers an especially interesting example of how this approach could work. Yuba Water Agency is developing an additional spillway below the existing spillway gates. The proposed Atmospheric River Control Spillway would allow operators to release water earlier when forecasts predict a major storm and downstream conditions can safely accommodate the additional flow. The project remains in development, however, so it will not provide additional capacity for this winter.

The larger lesson is important: California does not necessarily need another giant reservoir to capture more water. Better forecasts and smarter operations can sometimes create more useful flexibility within existing infrastructure.

The Ground Beneath Us Is Part of California’s Storage System

Groundwater is another major piece of the puzzle. California’s groundwater basins can store enormous amounts of water without a new dam. During wet periods, water can be diverted and allowed to seep underground, where it can remain available for future use.

The State is increasingly treating groundwater recharge as part of its overall water-storage strategy. The Department of Water Resources reports that local groundwater sustainability agencies reported an average of about 2.5 million acre-feet of managed recharge per year during Water Years 2022 through 2024, for a reported total of about 7.4 million acre-feet over those three years. That is a significant amount of water, but groundwater recharge has limits, too. A groundwater basin can absorb water only so quickly, some areas lack sufficient recharge facilities, and others may not have suitable soils or groundwater conditions. Recharge projects also must address water rights, water quality, groundwater management and environmental requirements.

This is another reason why preparation before a storm matters. If an agency waits until floodwaters are already moving downstream to determine where the water could go, whether it can legally be diverted and whether there is enough infrastructure to recharge it, the opportunity may already be gone.

The Biggest Projects Are Still Years Away

California is also pursuing major projects that could improve its ability to capture and store water in future wet years. Sites Reservoir, a proposed 1.5-million-acre-foot off-stream reservoir in the Sacramento Valley, remains in development, with permitting, funding, and other work still underway. The project is expected to become operational in the 2030s.

The proposed Delta Conveyance Project would take a different approach, adding new Sacramento River intakes and a tunnel to improve the State Water Project’s ability to capture and move water during high-flow periods. DWR views the project as part of California’s effort to adapt to changing hydrology, including a shift toward more precipitation falling as rain rather than snow. Together, these projects could give California more flexibility to capture and store water during future wet years, but neither will help with the storms that may arrive this winter.

That creates an interesting gap in California’s water strategy. We need long-term investments, but we also need to be ready for the storms that arrive before those projects are finished.

So, Is California Ready?

California is better prepared than it was. The State has expanded groundwater recharge, created new permitting tools, improved weather forecasting, developed more flexible reservoir operations and begun planning major investments in storage and conveyance. But California still cannot capture every drop produced by a very wet winter.

How much water California can actually use will depend on where the storms occur, how quickly runoff arrives, how much space is available in reservoirs, how much water the conveyance system can move, whether the water is legally available for diversion, whether groundwater basins can absorb it, and what environmental and operational requirements apply at the time. A wet winter also brings risks of its own. Heavy rain can cause flooding, landslides, erosion, debris flows and water-quality problems. More water is not necessarily better if it arrives too quickly or in the wrong place.

For businesses, property owners, developers and agricultural operations, these issues can have practical consequences. Projects involving groundwater recharge, stormwater capture, surface-water diversion or water storage can raise questions about water rights, CEQA, permitting, water quality, groundwater regulation and competing beneficial uses.

So if this El Niño produces the kind of winter California is hoping for, the most important question may not be how much rain falls. It may be how much of that water California can actually capture and put to use.

When the storms come, having water is only part of the equation. California also needs the infrastructure, legal authority, permits, environmental protections and operational flexibility to act while the water is there—and that window may last only a few very wet days.