Freshwater shortages could double the effects of climate change on agriculture yields, a new study combining climate, agricultural and hydrological models found.

Published in the Proceedings of the National Academy of Sciences, the study estimates that climate change alone could result in a loss of between 400-2,600 petacalories of food supply, or 8 to 43 percent of present day levels. Add projected declines of freshwater into the mix and this could jump an additional 600-2,900 petacalories, the models showed.

The study represents a unique blend of research designed to give a more complex and honest look at where the planet is headed.

"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," said co-author Joshua Elliott, a research scientist with the Computation Institute's Center for Robust Decision Making on Climate and Energy Policy, Argonne National Laboratory. "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."

While both account for climate, the two models differ substantially in what they measure. Agricultural models are mainly designed to simulate how temperature, precipitation and other factors alter crop yield, while hydrological models estimate factors stream flow, water availability and storm runoff.

The results from the two overlapped when it came to estimates of the amount of water used for agriculture, but veered far from each other in terms of future demands for freshwater irrigation.

By peering deeper inside the mechanics behind the two, the researchers found discrepancies in how hydrological models account for processes such as the carbon cycle and crop water productivity when compared to agricultural models - a discovery that could help ensure greater accuracy in existing models.

Of the results, Elliott concluded: "It's a huge effect, and an effect that's basically on the same order of magnitude as the direct effect of climate change."

There is hope yet, the researchers found, should nations pursue measures such as redistributing water from areas projected to see an excess. 

"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."