Looking to the Distant Past to Understand Future Droughts

December 6, 2011 | 11:01 AM

By Terrence Henry

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 (NASA’s Goddard Institute for Space Studies)

This map shows rainfall declines during the Mayan civilization as a result of converting forest to farmland.  

New research by NASA of early droughts in Central America shows that deforestation can lead to droughts. A climatologist at the agency found that ancient civilizations like the Mayans and Aztecs made droughts worse “by clearing rainforests to make room for pastures and farmland.”

The research shows that when forests are replaced with farmland, it essentially makes the surface more reflective, and that affects rainfall. “Farmland and pastures absorb slightly less energy from the sun than the rainforest because their surfaces tend to be lighter and more reflective,” Ben Cook, the climatologist who authored the report, said in the report. “This means that there’s less energy available for convection and precipitation.”

NASA says that the pre-Colombian era “saw widespread deforestation” on the continent. Rainfall declined as much as twenty percent between 800 C.E. and 950 C.E., which corresponds with the period the Mayan civilization peaked and “abruptly collapsed.” “During the post-Columbian period,” the report says, “forests regenerated as native populations declined and farmlands and pastures were abandoned.”

“I wouldn’t argue that deforestation causes drought or that it’s entirely responsible for the decline of the Maya,” Cook says in the report, “but our results do show that deforestation can bias the climate toward drought and that about half of the dryness in the pre-Colonial period was the result of deforestation.”

Read the full report from NASA.