Time Between Precipitation Events Growing Longer In The West

Apr 14, 2021

Dry periods are getting longer in the West.
Credit Tom Koerner, U.S. Fish and Wildlife Service

The time between precipitation events in the West is increasing. That could have negative effects on ecosystems and wildfires.

Joel Biederman, a hydrologist at the U.S. Department of Agriculture, said many scientists have looked at long term trends in rainfall and temperature. But this study was the first to examine the timing between precipitation events.

"The changes in the total rainfall amount, a few percent [decrease] over the last 50 years. The changes in the temperature, fairly important, a few degrees [increase] over the last 50 years," he said. "But the changes in the dry intervals between rainfall events in some places have increased much more."

Biederman said some places saw as high as a 50 percent increase in the length of the average dry period. He said that's important for plants. Take for example, an experiment with a lima bean sprout.

"If we think about watering it a tiny amount every day, that's what a lima bean likes," said Biederman. "The other extreme would be if you took all the water that it would need in a month and you measured that out and then you dumped it all on in one day, and then you didn't water it for the next 29 days. It wouldn't do very well."

More frequent rainfall also helps prevent wildfire conditions, so Biederman said increases in dry periods could mean more severe fires.

His team is now conducting experiments on desert grasslands to test exactly how longer dry intervals impact the system.

Have a question about this story? Please contact the reporter, Ashley Piccone, at apiccone@uwyo.edu.