Drying Up

Tropical rainforests aren’t just havens of biodiversity; their large rivers also make them promising sources of hydropower. But logging could reduce potential energy production, scientists say.

Hydropower depends on river discharge, which is essentially the amount of water gained through rainfall minus the amount lost through evaporation. Clearing trees decreases evaporation, so hydropower plant designers often predict that deforestation will boost energy output. But deforestation also can reduce rainfall, the study authors say in Proceedings of the National Academy of Sciences.

The team analyzed the Xingu River basin, the site of a major new hydropower complex in the Amazon. If the researchers ignored the effects on climate, they found that clearing 20 to 40 percent of the forest increased river discharge by 4 to 12 percent. But if they took climate effects into acount, “the response is reversed,” they write. Clearing 15 to 40 percent of trees cut river discharge by 6 to 36 percent.

As a result, the plant’s average power production each year might reach only a quarter of its maximum capacity, the team predicts. Similar problems could arise at hydropower plants in tropical forests in Africa and Asia. Roberta Kwok | 14 May 2013

Source: Stickler, C.M. et al. 2013. Dependence of hydropower energy generation on forests in the Amazon Basin at local and regional scales. Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1215331110.

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