Periods of intense drought and extreme rainfall are happening more often because of global warming, according to a new study that looked at decades of satellite observations to confirm the link.
“While there have been predictions from climate models and scientists that droughts and pluvials will become more frequent and intense as the world warms, as well as anecdotal evidence based on what we see, this theory has been difficult to prove,” Matthew Rodell, a NASA hydrologist and co-author of the study, told weather.com. “Our study was the first to use global, satellite based observations of terrestrial water storage … to show that water cycle extremes have become more frequent.”
By looking at the sum of groundwater, soil moisture, lake and river water, and snow and ice — or “all the water stored on and in the land” — Rodell and the team discovered that there were four extreme water cycle events from 2015 to 2021, which happened to be the seven hottest years in the modern record. Between 2002 and 2014, there were only three major events per year.
“Further, we found a strong, significant correlation between global mean temperature and global total intensity of droughts and pluvials, which had never been shown before,” said Rodell, who is deputy director of Earth sciences for hydrosphere, biosphere and geophysics at NASA’s Goddard Space Flight Center.
As weather.com meteorologist Kait Parker explains, “Warmer air temperatures cause evaporation to increase, leading to faster on-set and longer-lasting droughts, but that moisture has to go somewhere, which is what is helping to cause extreme rainfall events. For every degree celsius the temperature rises, the atmosphere can hold 7% more water. That increased water vapor is contributing to the increased frequency of extreme rainfall events.”
For the study, published in the journal Nature, the researchers looked at observations from the GRACE and GRACE-FO satellites to characterize 1,056 extreme events from 2002 to 2021.
The most intense event identified was an extreme rainfall event, or pluvial, that began in 2019 in central Africa and is still going. Lake Victoria, on the boundary of Kenya and Uganda, has risen by more than 3 feet because of the rain.
The most intense dry event of the past two decades was a drought in Brazil in 2015 and 2016 that emptied reservoirs and led to water rationing in some cities.
“Both events were associated with climate variability, but the Brazilian drought occurred in the warmest year on record (2016), reflecting the impact of global warming,” Bailing Li, the other author on the study, said in a NASA news release. “The recent southwestern U.S. and southern Europe droughts were also some of the most intense events, in part, due to anthropogenic warming.”
The study also tested the correlations between global total intensity and other major climate indicators such as El Niño Southern Oscillation.
“While ENSO and the other oscillations certainly have some influence, they are not nearly as well correlated as global mean temperature is,” Rodell said.
“Our study suggests that as the world warms, the frequency and intensity of droughts and pluvials will continue to grow, but the specifics are impossible to predict,” he said.
Rodell said he’s hopeful that continued development and adoption of renewable sources of energy and energy-efficient technologies will lead to a reversal in the current course of climate change.
“Continued monitoring is key, as it provides the impetus for action,” he said. “… We must continue to develop and implement innovative methods for tracking and understanding climate change.”
