Droughts Longer, Rainfall More Unpredictable in the Western US
Drought has become a serious issue in America’s West. Not only are the region’s temperatures steadily rising and its annual rainfall totals falling, but dry periods between rains have become longer and annual rainfall is less predictable, according to a study published jointly by the US government’s Agricultural Research Service (ARS) and the University of Arizona.
ARS research hydrologist Dr. Joel Biederman reported that annual rainfall totals across the West have declined by an average of four inches in the past five decades, with the longest dry spell in each year increasing from twenty to thirty-two days.
“The greatest changes in drought length have taken place in the desert Southwest. The average dry period between storms in the 1970s was about 30 days; now that has grown to 45 days,” Dr. Biederman said. The growing fluctuations in drought and rain patterns are the study’s most significant finding, he said.
“Consistency of rainfall, or the lack of it, is often more important than the total amount of rain when it comes to forage (dry and green fodder) continuing to grow for livestock and wildlife, for dryland farmers to produce crops, and for the mitigation of wildfire risks,” Dr. Biederman said.
The rate of change also appears to be accelerating, with greater parts of the West showing longer drought intervals after the year 2000 when compared to previous years.
“For regions such as the desert Southwest, where changes clearly indicate a trend toward longer, more erratic droughts, research is urgently needed to help mitigate detrimental impacts on ecosystem carbon uptake, forage availability, wildfire activity, and water availability for people,” said co-senior author Dr. William K. Smith of the University of Arizona.
This article is based on the following bulletin released by ARS: https://content.govdelivery.com/accounts/USDAARS/bulletins/2cb6d8b