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When Earth Speaks to Sky

Research connects soil moisture to next-day rainfall

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Damp soil in the western United States indicates a higher probability of rain the next day. But the opposite is true in the eastern US, where dry soil means rain is more likely tomorrow. Photo by cgouin/iStock

In 1881, a land speculator named Charles Dana Wilber wrote a book called The Great Valleys and Prairies of Nebraska and the Northwest, in which he, stumping for western settlement, coined a phrase: “Rain follows the plow.”

The phrase captured a popular theory of climatology—that homesteading and farming could permanently change the climate of the arid West, increasing rainfall and turning the Great American Desert, as it was known, into a verdant paradise.

The idea, though lyric, turned out to be false. But scientists—as well as farmers, water managers, and urban planners—remained intrigued by the notion that soil and rain are somehow linked. Now, two scientists using comprehensive satellite data and sophisticated statistical techniques have proved that they actually are linked—but in an unexpected way.