It’s been one of the wettest years in California since records began. From October 2022 to March 2023, the state was blasted by 31 atmospheric rivers—colossal bands of water vapor that form above the Pacific and become firehoses when they reach the West Coast. What surprised climate scientists wasn’t the number of storms, but their strength and rat-a-tat frequency. The downpours shocked a water system that had just experienced the driest three years in recorded state history, causing floods, mass evacuations, and at least 22 deaths.

Swinging between wet and dry extremes is typical for California, but last winter’s rain, potentially intensified by climate change, was almost unmanageable. Add to that the arrival of El Niño, and more extreme weather looks likely for the state. This is going to make life very difficult for the dam operators tasked with capturing and controlling much of the state’s water.

Like most of the world’s 58,700 large dams, those in California were built for yesterday’s more stable climate patterns. But as climate change taxes the world’s water systems—affecting rainfall, snowmelt, and evaporation—it’s getting tough to predict how much water gets to a dam, and when. Dams are increasingly either water-starved, unable to maintain supplies of power and water for their communities, or overwhelmed and forced to release more water than desired—risking flooding downstream.

But at one major dam in Northern California, operators have been demonstrating how to not just weather these erratic and intense storms, but capitalize on them. Management crews at New Bullards Bar, built in 1970, entered last winter armed with new forecasting tools that gave unprecedented insight into the size and strength of the coming storms—allowing them to strategize how to handle the rain.

First, they let the rains refill their reservoir, a typical move after a long drought. Then, as more storms formed at sea, they made the tough choice to release some of this precious hoard through their hydropower turbines, confident that more rain was coming. “I felt a little nervous at first,” says John James, director of resource planning at Yuba Water Agency in northern California. Fresh showers soon validated the move. New Bullards Bar ended winter with plumped water supplies, a 150 percent boost in power generation, and a clean safety record. The strategy offers a glimpse of how better forecasting can allow hydropower to adapt to the climate age.

Modeling studies have long suggested that better weather forecasts would be invaluable for dam managers. Now this is being confirmed in real life. New Bullards Bar is one of a half-dozen pilot sites teaming up with the US Army Corps of Engineers to test how cutting-edge forecasting can be used to optimize operations in the real world. Early tests of the methods, called forecast-informed reservoir operations, have given operators the confidence to hold 5-20 percent reserve margins beyond their reservoirs’ typical capacity, says Cary Talbot, who heads the initiative for the Army Corps.

To Talbot, FIRO could mean a paradigm shift in how the Corps and others run dams. Historically, dam operators under the Army Corps umbrella had to ignore weather forecasts and respond only to rain and snow that was already on the ground. This rule traces back to the notorious capriciousness of traditional forecasts: If an operator takes a bad gamble on a forecasted weather event, the results can be dangerous. But in practice, this forces operators to react later than their gut tells them to, says Riley Post, a University of Iowa researcher who spent over a decade as a hydraulic engineer for the Corps. They might, for example, be expected to hold water in a nearly full reservoir even as heavy rains approach.

Recent developments, however, have sharpened the trustworthiness of forecasts, particularly for atmospheric rivers on the West Coast. Leaps in computing power have enabled ever-more-muscular climate and weather modeling. To pump these models with data, scientists led by the Scripps Institution of Oceanography have since 2016 launched reconnaissance flights over atmospheric rivers of interest, where they release dozens of dropsondes, sensor packs shaped like Pringles cans. The result is a detailed profile of a storm’s strength, size, and intentions, which can then feed into FIRO.

These reports aren’t clairvoyant; all weather forecasts involve a measure of uncertainty. But a dam operator with increased confidence in when, where, and how much water will strike their watershed can take a more “surgical” approach to holding or releasing water, Post says.

And if they know how much time they have, they can also make the most of their existing water. Take Prado Dam, a vintage 1941 facility that was built to shield Orange County from flooding but can also distribute water to 25 groundwater-recharge stations. This past winter, forecasts showed a well-spaced parade of storms tracking its way. So operators pulsed water from the dam into storage at an optimal cadence, giving it time to soak into the landscape. Adam Hutchinson of the Orange County Water District, which manages the groundwater-recharge system, said publicly in July that these actions delivered an “exceptional” boost to water supplies for “those dry years we know are coming.”

Jinsun Lim is an analyst with the International Energy Agency think tank who studies climate resilience in the energy sector. Lim says that this sort of specificity is exactly what hydro officials in many countries wish for: tools that can translate climate impacts at a local level for their unique watersheds and infrastructure. Talbot hasn’t seen anything quite like FIRO deployed abroad, but he says that curious parties from the UK, Chile, Southeast Asia, Australia, and other regions have contacted him. Meanwhile, other corners of the hydro world are applying similar logic to their own climate challenges.

For BC Hydro, which serves 95 percent of British Columbia’s population, heat waves have proven a bigger problem than drought. Rivers and rains remain strong, but the province’s historically mellow springs and summers have warmed up, prompting many people to switch on air conditioners, which jacks up power demand. To keep the ACs humming, BC Hydro keeps a close eye on its fuel supply, that is, its watershed. About 150 monitoring stations, equipped with snow, climate, and surface-water sensors, enable a near-real-time picture of water flows. This helps operators store up water for demand spikes in summer and winter alike.

Tajikistan, which gets fully 98 percent of its power from hydroelectricity, is adapting its fleet with a mix of hard and soft measures. Renovations at the 126-megawatt Quairokkum power plant, built in 1956, were screened against a range of climate scenarios—such as the diminution of its source glaciers. Just replacing its six Soviet-era turbines will hike output to 170 megawatts; the dam will also be reinforced for a 10,000-year flood whose intensity could exceed the previous design standard by anywhere from 15 to 70 percent. Meanwhile, investments by international funders in HydroMet, the country’s long-dysfunctional meteorology service, are paying off: The agency recently gave power generators early notice of a dry year, enabling forward planning.

Recent trends have underlined the need for such changes. Earlier this year, the International Energy Agency said today’s hydropower facilities are on average 2 percent less productive than dams were from 1990 to 2016. Droughts have weakened flows at many plants, the agency said, leaving fossil-based energy to fill a gap the size of Spain’s annual power use. Other dams have been exposed to extreme events for which they weren’t strictly engineered, as in north India in 2021, when a crumbling glacier sent forth a wall of water that wrecked dams and towns downstream. Last month’s disaster in Libya, due to the failure of two flood-control dams hit by a supersized Mediterranean storm, further underlines the risks of maladapted facilities.

Even hydropower’s harshest critics take no issue with nip-and-tuck improvements at today’s dams. But amid a massive expansion planned in the Global South, they warn against overconfidence that hydropower can adapt its way out of climate change. In July, an environmental group in Namibia urged the government to rethink a large dam proposed for the Kunene River, saying it’s prone to the same climate extremes that have sapped the energy of Namibia’s other dams.

As climate disruption sets in, solar and wind can provide equivalent power with less risk, says Josh Klemm, co-executive director of International Rivers, a human rights organization focused on river communities. “We need to really reexamine plans to develop new hydropower,” he says. “We’re only going to deepen our reliance on a climate-vulnerable energy source.”

The Army Corps, meanwhile, is in the early stages of studying whether FIRO can be attempted at 419 other dams under its umbrella. Scaling up FIRO isn’t entirely straightforward; other parts of the US have different kinds of precipitation events than California does, and some of these are currently a lot harder to predict than atmospheric rivers. But Talbot is optimistic that the ever-improving forecast science can find efficiency gains there for the taking. “It’s making your existing infrastructure work harder for you,” he said. “In the face of climate change, this sounds like a great way to position ourselves for buffering that.”