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02/24/2025
By Katharine Webster

The rapid and devastating spread of the Los Angeles fires was fueled in part by greater extremes of wet and dry weather, a pattern called 鈥渉ydroclimate whiplash鈥� or 鈥渉ydroclimate volatility鈥� that is accelerating because of global warming, says Environmental, Earth and Atmospheric Sciences (EEAS) Assistant Professor Christopher Skinner.

鈥淭he last two years in LA have been extremely wet, so there was a lot of buildup of vegetation,鈥� Skinner says. 鈥淭hen, beginning last spring, it was extremely dry. The rainy season didn鈥檛 start on time and all that vegetation dried out, and then the Santa Ana winds came.聽

鈥淎ll the ingredients were there for a massive wildfire, and once that spark was lit, it spread so fast that there was no way to fight it,鈥� he says.

Now, the Los Angeles area is experiencing heavy rains, which are causing mudslides because the vegetation that helps hold the soil together has burned up, he says.

鈥淭hat鈥檚 why we care about these whiplash events,鈥� he says.

Skinner recently co-authored a that looked at changes in precipitation patterns around the world and found that sudden, large or frequent switches between very wet and very dry conditions increased by up to 66% from season to season and up to 31% from year to year since the mid-20th century. The paper was published by Nature Reviews Earth & Environment on the day the LA wildfires began.

Skinner sat down with us to talk about hydroclimate volatility. The interview has been edited for length and clarity.

Q: How does hydroclimate whiplash work, and why is it accelerating?

A: It helps to think of the atmosphere as a sponge. For every 1 degree Celsius that global average temperatures rise, the size of the sponge grows exponentially by 7%. When it鈥檚 hot, the atmospheric 鈥渟ponge鈥� can hold more moisture, and then when something squeezes out the sponge, more water is released as precipitation.聽

At the same time, rising temperatures increase the rate at which water evaporates from the earth鈥檚 surface. That means dry spells are more likely to be severe.

Q: How is this pattern of wet-dry volatility affecting the Northeastern U.S.?

A: We鈥檝e seen more of these torrential rains that cause flash flooding. In September 2021, Hurricane Ida dumped so much rain on New York that it overwhelmed the city鈥檚 storm drainage systems, and more than a dozen people died when their basement apartments suddenly flooded.

In September 2023, Leominster, Massachusetts, got hit with 11 inches of rain in a few hours. Rapid flooding opened sinkholes and washed out roads and train tracks. This past fall, we had extremely dry weather in Massachusetts, and it was the most active wildfire season I can remember 鈥� maybe on record. And because the trees and other vegetation were so dry, the fires spread faster and farther than normal.

Q: What are some of the most serious effects of hydroclimate whiplash?

A: It鈥檚 a huge challenge for agriculture. Increasingly, farmers in more traditionally temperate areas of the country like the Northeast need irrigation systems, which are very expensive. At the same time, they need to have drainage systems for those heavy rains. Farmers also need help developing crops that can tolerate both severe heat and soggy soils.

Hydroclimate volatility also requires a different approach to infrastructure. When it鈥檚 hot and the soil gets very dry, it can鈥檛 absorb as much water, so there鈥檚 more runoff, which also contributes to flooding. Dams that were built to prevent flooding can be overtopped or fail during these extreme rainfall events.聽

Around the world, we need to design and build infrastructure that can handle heavy rainfall while capturing more of that water for storage and use when conditions are dry.

Q: Where is climate volatility the worst?

A: Globally, land masses closest to the equator are seeing the largest increase in hydroclimate whiplash events, especially from North Africa across the Middle East and in South Asia. We don鈥檛 know precisely why, but that鈥檚 what the data from weather stations around the world shows. My colleagues and I are working to better understand these changes.

Q: What kind of research are you doing in this area?

A: Professor Mathew Barlow and I are working on two major grants. Under a three-year, $478,000 award from the National Oceanic and Atmospheric Administration,聽we鈥檝e looked at how heat waves and droughts interact in the Northeast. Heat waves can lead to droughts, but oftentimes, droughts can make temperatures during heat waves much hotter.

We鈥檝e also looked at the different 鈥渇lavors鈥� of heat waves. Here in the Northeast, we have four different types, and we鈥檝e been trying to figure out if some of them are more predictable than others.聽

Finally, to better understand why droughts form, we鈥檝e looked at where the moisture comes from for our rainfall. We have found that a lot of it comes from the Gulf of Mexico and the mid-Atlantic to the subtropical Atlantic, which means that monitoring conditions in these areas may help us to better predict droughts here.

We also just got a four-year, $400,000 grant from the National Science Foundation to look at how climate change influences vegetation and how the changes in vegetation feed back onto the climate. For example, when vegetation blooms a little earlier in the year, as it has been doing with the recent warmer springs we鈥檝e had, it draws moisture out of the soil earlier, and that can influence the likelihood of spring flooding.

All of this is to try and understand what the mechanisms are behind these high-impact events and whether we can improve their predictability.