California Needs Water. But El Niño Could Bring More Than It Can Store

California has spent years worrying about not having enough water. Now the state is preparing for a different problem: what if too much arrives at once?

A powerful El Niño is developing in the Pacific, raising the likelihood of a wetter-than-normal winter across California. For a state that has spent more than two decades dealing with drought and water shortages, the prospect of heavy rain and mountain snow might appear to be straightforward good news. But California’s water problem is not simply about how much rain falls. It is also about how much of that water can be captured, stored and used later. 

El Niño tends to shift atmospheric circulation in ways that increase the chances of storms reaching California. Some of these storms can arrive as atmospheric rivers, transporting enormous amounts of moisture towards the West Coast. The current event is forecast to be unusually strong, although El Niño does not guarantee that every part of California will receive abundant precipitation. That uncertainty matters because California’s water infrastructure has to manage both extremes: prolonged dryness and sudden torrents.

When Too Much Rain Becomes a Water-Storage Problem

During a major storm, rivers can rise rapidly and reservoirs can fill quickly. If reservoirs cannot safely hold additional water, managers may have to release flows downstream. Some water can also move rapidly through channels and eventually reach the Pacific before it can be stored for future use.

This creates an unusual contradiction. A state can experience flooding during a wet winter and still face water shortages during the following dry season. California has been improving its ability to capture stormwater. One increasingly important approach is groundwater recharge. Instead of trying to store every drop in surface reservoirs, water can be diverted into spreading grounds, floodplains or agricultural areas where it infiltrates the soil and replenishes underground aquifers.

Los Angeles County, for example, has expanded the use of spreading grounds where stormwater can be held temporarily and allowed to seep into the ground. Similar efforts are underway in the Central Valley, where floodplains, recharge basins and farmland are being used to capture water during large storms. Groundwater offers an important advantage: it does not evaporate from an exposed reservoir in the same way, and it can provide a buffer during future dry periods. But groundwater recharge also depends on suitable geology, available infrastructure, water rights and the ability to move stormwater to locations where it can safely infiltrate.

California has also learned that simply building more storage is not enough. Water has to be available in the right place and at the right time. A reservoir may have capacity while a flood is occurring somewhere else, yet moving that water can be difficult or impossible during a major storm.

The Bigger Challenge Is Managing Extremes

California’s experience reflects a broader shift in water management. Climate change is making the traditional assumption of a predictable seasonal water cycle increasingly difficult to rely on. Warmer temperatures can increase evaporation and alter the balance between rain and snow, while changes in the timing of runoff can complicate reservoir operations.

At the same time, a strong El Niño can produce individual storms capable of delivering enormous quantities of water in a short period. Historical El Niño events show that some very strong events have produced exceptionally wet conditions in California, but the relationship is not perfect. The 2015-16 El Niño, for example, did not produce the same statewide precipitation outcome as some earlier strong events. That means California cannot simply wait for El Niño to refill its water system. The opportunity is to use unusually wet periods more effectively while reducing the damage caused by the same storms. Restoring floodplains, expanding groundwater recharge, improving reservoirs and creating more places where excess stormwater can safely spread across the landscape could allow more water to remain available after the storms have passed. There is a limit, however, to how much water can realistically be captured. Flood control, environmental flows, groundwater conditions, infrastructure capacity and public safety all place constraints on what can be diverted and stored.

California therefore faces a paradox that may become increasingly common: the same climate system can produce both water scarcity and water abundance, sometimes only months apart.

The coming El Niño winter will test how well the state can manage that contradiction. The question is not simply whether California gets rain. It is whether the state can turn intense rainfall into reliable water supplies without turning the storms themselves into disasters. For a drought-prone state, that could be the more important measure of water security.

References: 

https://www.nytimes.com/2026/09/26/climate/el-nino-california-water-drought.html

https://www.noaa.gov/news-release/el-nino-forms-expected-to-strengthen-say-noaa-forecasters

https://ui.adsabs.harvard.edu/abs/2016AGUFM.A41L..08J/abstract

https://pw.lacounty.gov/core-service-areas/water-resources/spreading-grounds

Banner Image: AI Generated

Sections of this article may have been developed with the assistance of artificial intelligence tools to support research, drafting, and language refinement. All information has been reviewed, edited, and verified by the author/editor to ensure accuracy, context, and editorial integrity. The responsibility for the final content, interpretations, and conclusions rests solely with the publisher.