Models uncertain about climate change impact on soil moisture

Models uncertain about climate change impact on soil moisture

Study aims to answer how soil will react to climate change in the Midwest

A Dartmouth-led study is asking the question that's sure to be important to farmers across the Corn Belt: Will the U.S. Midwest trend drier or wetter with projected climate changes?

Related: USDA lays out broad climate change mitigation plan

While the researchers ultimately find that the answer is uncertain, their study is one of the few to examine the response of soil moisture to climate change, and still fewer have assessed soil moisture using a combination of model simulations and regional observations.

A Dartmouth-led study is asking the question that's sure to be important to farmers across the Corn Belt: Will the U.S. Midwest trend drier or wetter with projected climate changes?

Previous studies have focused more on surface air temperature and precipitation as it relates to climate change, but soil moisture is a key indicator of the water cycle, reflecting dynamics of precipitation, evaporation, plant transpiration and runoff.

A potential consequence of climate change, a Dartmouth summary said, is significant modification of the water cycle in heavy ag areas like the Midwest. It asserts that the study's findings are important, given the Midwest's agricultural output is critical to the U.S. economy and global food security.

A look at moisture predictions
The Dartmouth-led team ran multiple regional climate model experiments to project summertime changes in the water cycle over a representative area of the Midwest.

Some of their experiments predict drier soil conditions over the Midwest, while others predict wetter soil conditions, with the response strongly dependent on the choice of global climate model used to provide input to the regional climate model.

Related: Risks to ag, rural Midwest evident if no action taken on climate change

To resolve the contradictory predictions, the researchers also assessed an extensive and unique observational dataset of the water budget in Illinois. Their results show no statistically significant trends in soil moisture, precipitation, streamflow, groundwater level or surface air temperature over a recent 26-year period.

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Model simulations unanimously project increased temperatures in the Midwest, but the observed trend has been insignificant so far in contrast to climate trends across the world, where most places have already warmed.

"Based on our analysis of model simulations and regional observations, we conclude that climate change impacts on the water cycle of the Midwestern United States remain uncertain," says lead author Jonathan Winter, an assistant professor of geography at Dartmouth.

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"Our findings also suggest that while increases in surface air temperatures have been insignificant so far, adaptation to projected increases in temperature should be given priority as the signal is robust and could have large impacts on crop yields," he said.

Ultimately, Winter said the findings highlight a need for expanded study on soil moisture and improved simulations of soil moisture by climate models.

The study appears in the journal Water Resources Research. The study included researchers from Dartmouth College, Columbia University, National University of Singapore and Massachusetts Institute of Technology.

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