The world鈥檚 irrigated land has grown by more than 300,000 square kilometres since 2000. More than half of that increase occurred in places that lack enough water to irrigate without eventually running dry.
Around used by people goes toward irrigation, and irrigated lands produce food for 3.4 billion people. Irrigating rain-fed cropland could help grow food for an additional 1.4 billion people, and also help farmers adapt to climate change, says at Stanford University in California. But irrigation in places without enough water can deplete stores, threatening water security.
at the University of Delaware and his colleagues used statistics on irrigation infrastructure collected from 243 countries to see how irrigated land had changed in the 21st century.
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Their preliminary findings show that, between 2000 and 2015, the overall amount of irrigated land increased by 11 per cent to 3.3 million square kilometres. The greatest overall increase was in China, followed by India, then water-rich Brazil, where irrigated land more than doubled. Several regions saw a decrease in irrigation, including the drought-stricken western US, northern China and parts of Pakistan. Russia鈥檚 irrigated land declined by half.
The researchers then examined the amount of , considering both rainfall and groundwater. Of the places where irrigation increased, 52 per cent did not have enough water to support the new irrigation without eventually depleting available stores. Measured against a warmer climate, the amount of unsustainable irrigation is likely even greater than this count, says Rosa, who wasn鈥檛 involved with the study.
While much of the expansion in China, Egypt, Iran, Thailand and a number of other countries was unsustainable, the largest unsustainable expansion was in India 鈥� the country accounted for more than a third of all unsustainable new irrigation across the globe, notably in the fertile North Indian Plain.
鈥淚t鈥檚 very hot and water demands are very high,鈥� says at the Indian Institute of Technology Gandhinagar. Other factors contributing to new irrigation include more reliable electricity for pumping, and a new water-intensive summer corn crop. Because of concerns that groundwater will be sucked dry, the to help monsoon rainfall recharge aquifers.
鈥淚rrigation helps farmers in the short run adapt to climate change,鈥� says Mishra. 鈥淏ut if you look long term, we cannot go back鈥� once groundwater is depleted, he says.
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