Freshwater loss compounds climate change’s detrimental effects on agriculture
The researchers discovered discrepancies in how hydrological models incorporate processes such as the carbon cycle and crop water productivity when compared to agricultural models — a finding that will help make existing models more accurate.
“This is absolutely the first study in which a multi-model ensemble of hydrological models was compared to a multi-model ensemble of crop models,” Elliott said. “Several modeling groups have already changed the way that they are modeling the hydrological cycle with respect to crops because of the results of this paper.”
The comparison also produced new insight about the potential agricultural consequences of climate change. Due to climate change alone, the models predicted a loss of between 400 and 2,600 petacalories of food supply, 8 to 43 percent of present day levels. Due to the decline in freshwater availability, however — and the associated conversion of irrigated cropland to rain-fed — the models predict an additional loss of 600 to 2,900 petacalories, the researchers discovered.
While the models predict freshwater shortages in some areas of the world, such as the western United States, India, and China, other regions may end up with a surplus of freshwater.
Redistributing that excess water to restore or add irrigation to rain-fed crop areas could dampen some of the consequences of climate change upon irrigation and agriculture, Elliott said.
“We found that maximal usage of available surplus freshwater could end up ameliorating between 12 and 57 percent of the negative direct effects of climate change on food production,” Elliott said.
“However, there are lots of different political, economic and infrastructural reasons why you would consider that to be overly optimistic.”
The results are among several major findings reported in the ISI-MIP special issue of PNAS by the AgMIP group, which conducted a “fast-track” exercise to generate new knowledge about climate change impacts on agriculture for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.
“Understanding the climate change implications of freshwater availability is key to the future food security goals of society,” said Cynthia Rosenzweig, co-primary investigator of AgMIP and co-author of the paper. “The rigorous AgMIP multi-model approach is enabling advances in research on how climate change will affect agriculture worldwide and water is a vital component.”
The release notes that computing for this project was provided by a number of sources, including the University of Chicago Computing Cooperative, the University of Chicago Research Computing Center, and through the NIH with resources provided by the Computation Institute and the Biological Sciences Division of the University of Chicago and Argonne National Laboratory
— Read more in Joshua Elliott et al., “Constraints and potentials of future irrigation water availability on agricultural production under climate change,” Proceedings of the National Academy of Sciences (16 December 2013) (doi: 10.1073/pnas.1222474110)
