After years of drought, declining groundwater supplies, stressed rivers, and increasingly unpredictable weather, a major change is taking shape in the Pacific Ocean that could have significant implications for America’s water supply.
El Niño is here, and it is strengthening.
NOAA’s Climate Prediction Center currently expects El Niño to strengthen through the end of 2026, with a 97% chance that it will persist through early spring 2027. In its July 9 outlook, NOAA put the probability of a very strong El Niño during October through December at 81%, potentially placing this event among the strongest recorded since 1950. NOAA is also careful to point out that even the strongest El Niño events do not produce the expected weather pattern everywhere.
That uncertainty matters, but so does the potential opportunity.
As of August 4, 48.54% of the Lower 48 states were experiencing drought conditions, affecting more than 91 million people. A wetter winter across drought-stricken parts of the country could improve soil moisture, increase river flows, rebuild snowpack, recharge groundwater, and provide valuable inflows to reservoirs.
For parts of the American West, that water would be especially welcome.
If California’s Reservoirs Are Above Average, Why Are We Still Talking About Drought?
This is where the water story gets more complicated.
California has entered late summer with many of its major reservoirs near or above their historical averages. At first glance, that seems inconsistent with continued concern about drought and long-term water scarcity.
The first thing to understand is that “105% of average” is not the same thing as “105% full.”
Reservoir statistics frequently compare current storage with the historical average for that particular date. Those percentages do not represent physical capacity.
Lake Oroville provides a perfect example. On August 2, 2026, Oroville was at approximately 72% of its total capacity, yet it contained 106% of the amount of water normally stored there at that point in the year. Lake Berryessa was at 88% of capacity but 114% of average, while Shasta Lake was at 66% of capacity and 98% of average.
Those are encouraging numbers, but reservoirs are only one part of a much larger water system.
The Water We Cannot See May Be the Bigger Story
California relies heavily on groundwater, particularly during dry years when surface supplies become less reliable. More than 32 million Californians rely on groundwater for at least part of their water supply, and agriculture accounts for the majority of groundwater use in the state.
Unlike a reservoir, however, an aquifer cannot simply be observed from the side of a highway or measured by looking at a shoreline.
Decades of pumping have created significant groundwater deficits in portions of California. Wet years have helped, but they have not erased those deficits. In its 2026 hydrology update, the California Department of Water Resources reported that groundwater conditions have improved from the severe drought conditions of a decade ago, yet groundwater systems have still not fully recovered. The DWR says multiple consecutive wet years, combined with reduced pumping, will be necessary to achieve long-term aquifer sustainability.
That is one reason a powerful wet winter could be so valuable. The opportunity is not simply to put more water behind dams. It is also to move water underground through groundwater recharge when conditions allow.
California increasingly uses managed aquifer recharge projects to direct excess surface water into areas where it can infiltrate into underground aquifers. The DWR describes groundwater basins as a critical drought buffer, essentially functioning like a savings account that can be drawn upon when surface supplies become scarce.
Some Groundwater Loss Can Become Permanent
There is another reason groundwater cannot be restored overnight.
When groundwater is pumped excessively, underground layers of clay and sediment can compact as water levels decline. The result is land subsidence, where the ground itself begins to sink. In some circumstances, that compaction permanently reduces the amount of water an aquifer can store.
USGS research into California’s Central Valley found substantial groundwater storage losses associated with decades of pumping, including permanent losses caused by subsidence.
California’s latest statewide groundwater assessment shows that this is not simply a historical problem. The DWR reported in March that approximately 4,000 square miles of California experienced more than half a foot of subsidence during the previous five years.
A rainy winter can help groundwater levels recover. Rebuilding an aquifer that has been depleted over decades is a much longer process.
California Also Has a Giant Reservoir in the Mountains
California’s water system has another form of storage that is easy to overlook: snow.
The Sierra Nevada snowpack acts as a massive natural reservoir, accumulating water throughout the winter and gradually releasing it into rivers, reservoirs, and watersheds as temperatures rise. On average, Sierra snowpack supplies approximately 30% of California’s water needs.
Climate change is making that natural storage system less predictable. California DWR has documented declining snowpack, earlier snowmelt, warmer temperatures, more precipitation falling as rain rather than snow, and changes in the timing of runoff.
The 2026 water year provided a dramatic example. After an initially promising winter, record heat and dry conditions accelerated snowmelt so quickly that California’s April snow survey found virtually no measurable snow at the traditional survey location.
This is one reason water managers increasingly talk about weather “whiplash.” California can move from drought concerns to flooding concerns and back again remarkably quickly.
Why Can’t We Just Capture Every Drop?
Another common question during major rain events is why water is sometimes released from reservoirs or allowed to continue downstream instead of being stored.
Reservoirs have multiple jobs.
They provide water for communities and agriculture, support fish and wildlife, generate power, provide recreation, and, critically, protect downstream communities from flooding.
During the winter and early spring, reservoir operators may be required to preserve empty space so an incoming storm does not overwhelm the reservoir and create a dangerous flood situation. Earlier this year, DWR noted that major reservoirs such as Shasta and Oroville could not simply retain all of an unusually early snowmelt because sufficient space had to remain available in case a major late-season storm arrived.
Water stored behind a dam also serves cities, farms, environmental needs, downstream ecosystems, and other legally established purposes. A high reservoir level therefore does not mean every gallon is freely available for consumption.
The Other Side of El Niño: Flooding and Coastal Damage
If the 2026-27 El Niño develops as NOAA currently expects, the potential benefits to water supplies may arrive with serious risks.
El Niño can raise sea levels along the West Coast while changing storm tracks across the country. NOAA has warned that the developing event could contribute to more frequent, deeper, and more widespread high-tide flooding along portions of both the West and East Coasts. Along the West Coast, higher ocean levels combined with strong surf and high tides can push water farther inland. Along the Atlantic Coast, changes in the jet stream can increase storm surge risk.
Heavy winter storms can also produce flash flooding, landslides, overwhelmed stormwater systems, coastal erosion, and significant property damage.
That creates an interesting contradiction. The same winter that helps replenish water supplies can also create too much water, too quickly, in places where we do not want it.
El Niño Could Help, but It Cannot Solve the Water Crisis by Itself
A strong 2026-27 El Niño could provide meaningful drought relief. A productive winter could replenish reservoirs, improve soil moisture, rebuild mountain snowpack, increase river flows, and create valuable opportunities for groundwater recharge.
But one wet winter cannot undo decades of groundwater depletion, long-term changes to snowpack, growing demand, or the increasing volatility of the climate.
That is why water conservation remains important even when reservoirs look healthy.
For property owners and operators, the lesson is especially relevant. Water captured during a wet winter is still a valuable resource, and allowing thousands of gallons to disappear through undetected toilet leaks, plumbing failures, or other preventable water waste makes little sense simply because rainfall happens to be abundant that year.
Sensor Industries helps property teams identify that hidden water waste. SI-Flush Sensors monitor toilet fill activity to identify running toilets and leaks, while SI-Leak Sensors detect flowing or standing water in high-risk locations. Data moves through the SI-Mesh wireless network to SI-Dash, giving property teams 24/7 visibility, alerts, and information that can help them respond more quickly.
If El Niño delivers the wet winter much of the country needs, the opportunity goes far beyond watching reservoir levels rise.
It is an opportunity to capture more water, replenish what has been lost underground, strengthen supplies for future dry years, and become smarter about how we manage every gallon once we have it.