Higher Evaporation Rates Powered By Record Heat Increasingly Key Factor In Western Droughts

Dry wells. Dwindling reservoirs. Parched ground. Forest fires. The American West has gotten awfully familiar with drought in the 21st century. And it wouldn’t be the same without the heat. This summer, like many before, set new benchmarks for heat, as big swaths of the West, including Arizona and California, lived through their hottest summers on record.

These temperatures, even more than the amount of rainfall, are key to understanding drought in the climate change era, according to a new study in the journal Science Advances. The research found that since 2000, rising temperatures — leading to greater evaporation — have done more to contribute to the severity and extent of droughts in the West than a lack of rainfall. “This is quite different from our grandma’s drought,” said Rong Fu, a professor in atmospheric and oceanic science at UCLA who is one of the authors of the study.

Before hotter temperatures — driven by humans burning fossil fuels — droughts were caused by shifting weather patterns and fluctuating rainfall as part of a natural cycle, she said. But now, as long as the planet keeps getting warmer, evaporation is playing a dominant role and is “only going to increase.” “Even if you have rainfall,” she said, much of it won’t reach western reservoirs because it will evaporate along the way. “That has quite profound implications,” she said.

The long-term trend toward a drier West is not a new idea. Much has been written on this process of “aridification” as warming temperatures lead to longer and more intense droughts across the region. Others have documented how the two-decade megadrought in the West since 2000 amounted to the driest period for the region in more than 1,000 years.

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https://www.washingtonpost.com/climate-environment/2024/11/06/droughts-heat-rainfall-future/