Science Behind the Forecast: When the atmosphere gets thirsty

LOUISVILLE, Ky. (WAVE) - The National Weather Service defines a drought as “a period of abnormally dry weather sufficiently prolonged for the lack of water to cause serious hydrologic imbalance in the affected area.” In layman’s terms, a drought is a stretch of persistent, unusually dry weather that is extensive enough to cause water supply shortages and crop damage.

Evaporative demand or “atmospheric thirst” describes our atmosphere’s ability to pull moisture from the ground. A new study has found that the U.S.’s atmosphere has become a lot thirstier over the past four decades. Significant increases in “atmospheric thirst” are the leading causes of droughts, increases in the frequency and extent of forest fires, and reduced streamflows.

The study found the biggest increase in evaporative demand over the southwestern United States. Higher temperatures and low humidity, along with stronger winds and more solar radiation, all contributed to the evaporative demand. Atmospheric thirst conditions are now outside of the range of what was seen 20 to 40 years ago.

Researchers found temperature increases were responsible for 57 percent of the changes seen in all regions, with humidity (26 percent), wind speed (10 percent), and solar radiation (8 percent) playing lesser roles.

Analyzing atmospheric thirst is important when looking at potential impacts on water supply and farmers. Increases in atmospheric thirst may lead to more water being required to satisfy our existing water needs.

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