Rainfall across the US is increasingly coming from farther away
Before rain falls, the moisture that forms it may have traveled anywhere from just a few kilometers to hundreds or even thousands of kilometers away. It usually begins as water that evaporated from oceans, lakes, forests or fields. According to a paper published in Geophysical Research Letters, rain in parts of the United States is increasingly arriving from farther away.
Tracking the rainfall
Travis Aerenson of the University of Wyoming and his colleagues analyzed 35 years of data (1990–2024) from a high-tech climate record called ERA5. They then fed this historical information into a tracking computer model to trace the origin of the water that eventually fell as rain across 18 major watershed regions covering the lower 48 states.
To see if the way water moves through the air is changing, they split the 35-year record into two halves, comparing the earlier years with the later years.
The results showed that across parts of the United States, water vapor that turns into rain has been traveling longer distances and staying in the atmosphere longer. The strongest trends are happening in the Southwest and the southern Great Plains, where water vapor in some regions now travels about 50 to 80 kilometers (31 to 50 miles) farther and hangs in the air two to four hours longer on average than before.
"Moisture is being carried over greater distances and times in the atmosphere between its evaporation and precipitation than in previous decades," the study authors wrote.
The paper also revealed that across most of the study's watershed regions, a greater share of rainfall now comes from water that evaporated from oceans rather than land.
Winds of change
So what is the significance of all this? The researchers found that these changes appear to be driven by a combination of a warmer atmosphere holding more water vapor and changes in atmospheric circulation, such as Pacific storms moving farther north and stronger Gulf winds drawing summer moisture from the Caribbean. This is the case for the Arkansas–White–Red River Basin, where more summer rain now originates from the Caribbean.
Because the atmosphere is carrying this water for greater distances, local rain is becoming less connected to local land evaporation. This means that managing water supplies may require looking far beyond local state lines. And that could be a problem.
"As the trends in moisture transport continue and moisture sources become even farther from their eventual precipitation regions, the water security of nations and states will fall increasingly outside of their borders."
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Publication details
T. Aerenson et al, Precipitation Over the Contiguous United States Is Coming From Farther Away Than in the Past, Geophysical Research Letters (2026). DOI: 10.1029/2026gl122565
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Citation: Rainfall across the US is increasingly coming from farther away (2026, July 30) retrieved 30 July 2026 from https://phys.org/news/2026-07-rainfall.html
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