Mid-November weather news postings largely feature rain and snow, along with continued tropical weather formation. But drought is important, too -- and research on the western United States drought of 2020-22 finds higher temperatures caused by increased greenhouse gases turned an ordinary drought into an exceptional drought.
The research project also found evaporative demand, or the thirst of the atmosphere, has played a bigger role than reduced precipitation in droughts since 2000. During the 2020-22 drought, evaporation accounted for 61% of the drought's severity, while reduced precipitation accounted for only 39%.
The study was done by scientists from the University of California Los Angeles (UCLA), NOAA's National Integrated Drought Information System (NIDIS), and the Cooperative Institute for Research in Environmental Sciences (CIRES).
A summary of the study released by NOAA/NIDIS notes, "Historically, drought in the West has been caused by lack of precipitation, while evaporative demand played a smaller role. Climate change caused primarily by burning fossil fuels has resulted in higher average temperatures that complicate this picture. Now, droughts induced by natural fluctuations in rainfall still exist, but there's more heat to suck moisture from bodies of water, plants, and soil."
One of the features highlighted in the study's summary is how heating affects the atmosphere's capacity to hold water. Higher temperatures mean the warmer the planet gets, the more water can evaporate from the land and remain stored in the atmosphere longer before it returns to earth as rain or snow. Droughts can form even if precipitation patterns remain within a normal range as higher temperatures and evaporation remove water from the soil.
The scientists incorporated detailed observation data during the past 70 years to account for naturally occurring periods of drought. They found when natural weather patterns were included, greenhouse gas-related climate change accounted for 80% of the increase in evaporative demand since 2000. "During the drought periods, that figure increased to more than 90%, making it the single biggest driver of increasing drought severity and expansion of drought area since 2000," the study noted.
One of the lead scientists on the project, Rong Fu, a UCLA professor of atmospheric and oceanic sciences, addressed the inability of even normal precipitation to act as a buffer in drought formation. "Even if precipitation looks normal, we can still have drought because moisture demand has increased so much, and there simply isn't enough water to keep up with that increased demand," said Fu.
The 2020-22 drought also affected the U.S. Southern Plains, with notable reductions in winter wheat production along with extensive culling of beef cow herds due to a lack of adequate pasture, hay and water.
The full NOAA/NIDIS summary of the Western U.S. Drought Study is available here: https://www.drought.gov/…
Bryce Anderson can be reached at bryce.anderson@dtn.com
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