NASA: Mixed crops make cool, wet summers

Resembling a flying saucer, a powerful mesocyclone storm system swirls over the Great Plains

(CNN) -- The diversity of crops and vegetation in a large swath of the Western United States could contribute to cooler, wetter weather in the region, according to a NASA-funded study.

With satellite observations from Rocky Mountain and Great Plains states, scientists using computer climate models determined that vegetation patterns could influence atmospheric conditions enough to produce a wet chill.

"The mixed vegetation creates areas of different temperatures next to each other, some warmer and some colder, and this leads to mixing in the atmosphere that gives rise to clouds and, ultimately, rain," said meteorologist Jim Shuttleworth of the University of Arizona, Tucson.

Shuttleworth and colleague Lixin Lu of Colorado State University in Fort Collins published their report in the June issue of the Journal of Hydrometeorology.

The modeling suggests that agricultural development in the semi-arid region could have lessened drought, NASA said.

For instance, when dry, barren land is irrigated and covered with crops, the soil heats up the air less, the researchers said. The reason is that some of the solar energy that would normally reflect off the ground is used by the plants use for evaporation.

The temperature-changing effect varies with different kinds of crops, leading to air masses of different temperatures, which can generate storm clouds when they collide, the researchers said.

Moreover, the different heights of crops and trees in an area change the flow of the atmosphere, which increases air circulation and pushes up more air.

"When the rising air reaches the dew point in the cooler, upper atmosphere, it condenses into water droplets and forms clouds," said NASA's Goddard Space Flight Center in a statement.

The Greenbelt, Maryland-based center funded the study through its Land Surface Hydrology Program, which hopes to understand and predict the role of water in land-atmosphere interactions.

For their research, Shuttleworth and Lu re-created national weather trends but focused predictions on a rectangular region encompassing Colorado, South Dakota, Wyoming, Kansas and Nebraska.

Compared to less detailed computer climate models, which do not account for different kinds of vegetation, Shuttleworth and Lu's came up with cooler temperatures and slightly more rain, which could account for the lower temperatures, they said.