What a “Super El Niño” Could Mean for Orange County’s Water Supply
Kevin Hostert, Senior Water Resources Analyst, Municipal Water District of Orange County
October 1, 2026
As Orange County heads into the 2026–27 water year, all eyes are turning toward the above average sea surface temperature in the equatorial region of the Pacific Ocean. Forecasts point to an unusually strong El Niño, which means sea surface temperatures could be four to five degrees Fahrenheit above average along the equatorial Pacific this winter. This phenomenon, labeled a “Super El Niño,” has only happened three times before.
The first two times, winters of 1982-83 and 1997-98 brought a tremendous number of storms to California, especially in the south. The third time was the winter of 2015-16, when rainfall was not abundant, and California remained in its fifth year of drought.
Signs of a Strong El Niño are Already Here
Warmer-than-normal Pacific Ocean water has already allowed marine species normally found farther south to move north into Southern California. There have been reports of sightings of blue marlin, whale sharks, hammerhead sharks, and even sea turtles nesting in Huntington Beach.
Potential Rainfall Could Benefit Orange County’s Local Water Supply
For Orange County, one of the most important potential benefits of a wet El Niño winter is groundwater recharge.
Orange County relies heavily on its groundwater basin, managed by Orange County Water District, which provides a substantial portion of the region’s water supply. A very wet winter could fill the Orange County groundwater basin to levels not seen in decades. This would result in years of plentiful basin storage and would prevent the need for as much imported replenishment water.
What Does This Mean for Metropolitan Water District?
A wet winter could provide The Metropolitan Water District of Southern California (Metropolitan) with greater flexibility in managing its overall water-supply portfolio.
Improved California precipitation could benefit State Water Project supplies, increase reservoir storage, and improve conditions for groundwater-dependent agencies. At the same time, greater local precipitation could reduce the immediate need for imported water in some parts of Southern California.
For Metropolitan, that could provide additional flexibility in how it manages storage and deliveries in upcoming years.
But there is an important distinction when considering the Colorado River.
El Niño Does Not Automatically Solve the Colorado River Problem
A wet California winter does not necessarily translate into significantly more water in the Colorado River system.
The Colorado River Basin has its own distinct hydrology, including precipitation and snowpack conditions in the Upper Basin. Southern California can receive substantial rainfall while the Colorado River Basin remains comparatively dry.
This distinction will be particularly important as California, Metropolitan, and the other Lower Basin states continue working through the new operating guidelines for the Colorado River beyond 2026.
For Metropolitan, a strong California water year could improve flexibility on the State Water Project and potentially provide surplus water availability, while leaving many Colorado River issues unchanged.
In other words, a wet California winter and healthy reservoir levels along the Colorado River are not necessarily the same thing.
Potential Implications for 2027-28
The benefits of a strong 2026-27 winter could extend into the following water year.
If California receives substantial precipitation, the Sierra Nevada develops a healthy snowpack, reservoirs improve, and Southern California groundwater basins receive significant recharge, water agencies could begin 2027-28 with more water stored across multiple components of their supply portfolios.
That could reduce pressure on some imported supplies and give Metropolitan greater flexibility in managing its resources.
The Colorado River component, however, would continue to require separate consideration. Metropolitan’s ability to maintain Colorado River Aqueduct deliveries, manage its Lake Mead storage, and utilize Intentionally Created Surplus would continue to depend on the applicable operating rules, system conditions and available storage.
Therefore, the potential benefits of El Niño should not be viewed as eliminating the need for careful Colorado River planning.
A Wet Winter Would Be Valuable, But How Wet Matters
For Southern California, the coming winter could present an unusual opportunity.
A strong El Niño increases the possibility of significant precipitation, but the ultimate water-supply benefit will depend on several factors:
- Where storms make landfall
- How much precipitation Southern California receives
- How much falls as snow in the Sierra Nevada
- The frequency and trajectory of atmospheric rivers
- How much runoff can be captured in reservoirs
- How much rainfall infiltrates local groundwater basins
- Conditions in the Colorado River Basin
Taken together, these factors will determine whether the 2026-27 winter becomes simply a wet winter or a truly consequential water-supply year.
For Orange County, the most beneficial outcome would be a winter that combines substantial local rainfall with effective groundwater recharge and improved statewide imported-water conditions.
Looking Ahead
All signs point to a historically wet winter, but there are no guarantees. Whatever the season brings, we must be prepared to respond to the conditions Southern California may face; whether this winter is exceptionally wet or unusually dry. To stay informed on the latest information on statewide and local water resources, visit MWDOC’s Water Supply Report.