A high-velocity string of violent storm systems called “atmospheric rivers” have brought heavy rain and snowfall to California in recent weeks. But then again, this sudden flood is not enough to compare with years of constant drought.

The storms caused widespread flooding that killed at least 20 people. The incessant snowfall has also caused reservoirs to start filling up again and snow has accumulated in the Sierra Nevada mountain range.

Jay Land, an expert on the subject at the University of California, attributes the coexistence of floods and droughts to “the great diversity of California’s climate.”

The US state typically experiences late fall and winter rains, with many storms fed by so-called “atmospheric rivers”. On the other hand, it goes through long dry periods in spring and summer.

California’s water infrastructure—reservoirs, wells, and irrigation systems—has been built in part to deal with this seasonal weather imbalance. However, the state’s strategy to harvest water during wet periods and store it during dry periods is becoming “increasingly difficult to implement due to increasingly extreme events” as the climate continues to warm.

Recent rains have resulted in a rapid and strong flow of water into many of the state’s reservoirs.

Many have even returned or even exceeded their usual reserves, yet few can operate at one hundred percent of their potential.

California State Water Management Program Director Molly White said that if reservoir water levels continue to rise above normal levels, it could alleviate some of the deficits that have accumulated after years of extreme drought.

California’s natural climate is varied, with periods of dry weather interspersed with periods of wetter weather. But research shows that global warming caused by greenhouse gas emissions makes longer or more severe droughts more likely, and rainy years less likely.

Climate change will also lead to more extreme wet periods. Since warmer air can carry more moisture, “atmospheric rivers” (which are essentially long columns of water vapor) will be able to release more water and snow.

In California, winter is usually the wet season, the time of year when many of the state’s aquifers are replenished. But the snowmelt that begins in the spring and continues throughout the summer is also critical to replenishing them, as they typically provide 30 percent of the state’s water supply.

Newly developed storm systems are by far the biggest source of snow accumulation in the Sierra Nevada this winter. A record amount of water contained in snow in a season has been measured at several recording stations, reaching seasonally high levels that are rarely seen until late April, when snow accumulation usually peaks.

According to the California Water Resources Agency, as of January 17, the recorded water content in the snow was double that of last year.

“Atmospheric rivers” do not always bring more snow, as rainfall can exceed snowfall in high mountain areas. A phenomenon that may become more frequent as the climate continues to get warmer.

“There’s enough snow now,” said National Weather Service meteorologist Rich Tinker, who compiled the latest official US drought report. “But how it melts will play a role.” Snowmelt is usually slow and steady, but with a sharp increase in temperature, this stability can change.

Last year, an unusually wet early winter was finally followed by several dry months, which led to restrictions on water use in the summer. According to research, climate warming and abnormally high temperatures in spring and summer have contributed to faster snowmelt.

Storms in a row won’t equal three years that California has set drought records. It took many years to reach the current state of permanent drought, Gus Goodbuddy, hydrologist at the USDA’s National Water and Climate Center, said, adding that it will be difficult to reverse in just one season.

The article was published in The New York Times.