Soil "hotspots" affect rain

Computer models identify places of strongest interaction

Water in the soil influences rain © NASA
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The fact that precipitation affects soil moisture is nothing new, but scientists have now discovered that this relationship also exists in reverse: Water in soil can affect rain both regionally and globally.

Using a dozen computer models, a NASA researcher has pinpointed "hotspots" around the Earth where soil moisture severely affects rainfall during the Northern Hemisphere summer. The results were published in the current issue of the journal Science.

The hotspots are located in the Central Plains of North America, the Sahel, Equatorial Africa and India. Less intense hotspots were seen in South America, Central Asia and China. Randall Koster, scientist at NASA's Goddard Space Flight Center and head of the International Computer Modeling Initiative, said, "The study shows the best coverage of areas where moisture changes affect precipitation.

In the Global Land-Atmosphere Coupling Experiment (GLACE), Koster and his colleagues reproduced the same experiment in twelve different computer models. In each model, scientists compared rainfall behavior to two types of simulations: one in which soil moisture differed between simulations and one in which all simulations had the same soil moisture. Any increase in coincidence between reg region and humidity in the second simulation set indicates

Although the results of the models differed, the researchers were able to identify specific common patterns, including the hotspots where soil moisture had the greatest impact on precipitation. The hotspots were, as expected, all in the transition zone between wet and dry regions. In humid climates, the sun's energy and cloud formation play a greater role in evaporation rates than soil moisture. In dry climates, however, the lack of water leads to evaporation rates that are too low for them to have a significant impact on the atmosphere. display

The understanding of soil moisture levels and their relation to precipitation has implications for a wide range of scientific fields and applications. It could improve the seasonal forecast of rainfall and thus make water management predictable in the longer term. At the same time, however, the short-term weather forecast also benefits.

(NASA, 23.08.2004 - DLO)