The scientists hope that their analysis will help maintain a stable and sustainable food supply as the world contends with more severe weather over many agriculturally important areas, including much of North America.

"One key finding is that both maize and soy are most vulnerable to short-term droughts that occur during the reproductive stage of the growing season," Samuel Zipper told environmentalresearchweb. "This is worrying, because these short-term or ‘flash’ droughts are much harder to anticipate and plan for than longer-term, multi-year drought."

As the data highlight, maize is particularly sensitive to one-month drought occurring in July, while soybean, traditionally planted later than maize, is most sensitive to two-month drought occurring in August. What’s more, the drought sensitivity at short timescales is nonlinear for both maize and soybean yields as water stress in the crops, triggered by more extreme drought conditions, drives greater losses.

For these short-term impacts, irrigation was seen to be a very effective tool in mitigating damage to the crop. However, as the researchers point out, there are knock-on effects – for example, an over-reliance on irrigation can place an unsustainable demand on groundwater aquifers. Alternative strategies include the development of more drought-tolerant crops through advances in plant breeding and genetics, or a mixed landscape featuring a variety of crops with varying sensitivities to drought.

A more surprising observation was that shifts towards reduced drought sensitivity over time are prevalent in the northern and western parts of the study domain – NE Iowa, Nebraska, Minnesota and the Dakotas. Increased drought sensitivity, on the other hand, was seen to be more common in central and southeastern areas – Ohio, Kentucky, Tennessee, Illinois, southern Indiana.

"It’s an interesting result, although we didn’t set out to answer this question," said Zipper. "Work by other groups has found that as yield went up, sensitivity to drought also rose – basically, because yield was on a higher shelf, it was able to fall further. We're seeing these increases in drought sensitivity in places that have been historically very productive, so that's one potential cause. Local agricultural management, including the adoption of precision agriculture or changes in irrigation extent, could also cause shifts like the ones we observe, although these hypotheses remain to be tested."

The team, which included Jiangxiao Qiu and Christopher Kucharik, published their work in Environmental Research Letters (ERL).

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