Freshwater scarcity is a fact of life for people across much of the planet with agricultural production severely affected as irrigation at croplands already accounts for 70% of water use globally.
Much worse is to come, however, scientists warn. By the middle of the century, say the authors of a new study, water scarcity in agriculture will likely increase in a staggering 80% of the world’s croplands.
The team of experts behind the study has reached this conclusion after examining current and future water requirements for agricultural production worldwide to see the amount of water that will be available in three decades from rainwater and irrigation in various regions in the face of a fast-changing climate.
Specifically, they devised a way to measure and predict water scarcity in two major sources used in agriculture: water in the soil available for plants from rain (called green water) and irrigation from freshwater sources such as rivers, lakes and groundwater reservoirs (called blue water).
The extent of green water available for crops depends on the level of precipitation in a given area as well as on the degree of loss to runoff and evaporation. Other factors such as farming practices, soil types and the lay of the land also impact water availability in the soil. In addition, increased demands for water in coming decades and a changing climate will also have a bearing on green water sources.
“As the largest user of both blue and green water resources, agricultural production is faced with unprecedented challenges,” stresses Xingcai Liu, an associate professor at the Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences who was lead author of the study.
Liu’s team has found is that owing to climate change, agricultural water scarcity across the planet will worsen in as many as 84% of existing croplands with a loss of water supplies driving scarcity in about 60% of them. This is disconcerting, to say the least, as water scarity is bad enough as it is.
Over the past century, the scientists explain, demand for water worldwide has grown twice as fast as the human population. “Water scarcity is already an issue on every continent with agriculture, presenting a major threat to food security. Despite this, most water scarcity models have failed to take a comprehensive look at both blue and green water,” they note.
Changing precipitation patterns and evaporation levels caused by higher air temperatures from climate change will impact large swathes of cropland worldwide, according to the scientists. Yet not everywhere will the effects be the same with more water in some areas and less in others.
“Adding this important dimension to our understanding of water scarcity could have implications for agricultural water management. For example, Northeast China and the Sahel in Africa are predicted to receive more rain, which may help alleviate agricultural water scarcity. However, reduced precipitation in the midwestern U.S. and northwest India may lead to increases in irrigation to support intense farming,” the researchers observe in a statement on their findings.
With less green water available for crops in many areas, sustainable practices to conserve diminished sources will be key, the experts emphasize. “Mulching reduces evaporation from the soil, no-till farming encourages water to infiltrate the ground and adjusting the timing of plantings can better align crop growth with changing rainfall patterns. Additionally, contour farming, where farmers till the soil on sloped land in rows with the same elevation, prevents water runoff and soil erosion,” they explain.
“In the longer term, improving irrigation infrastructure, for example in Africa, and irrigation efficiency would be effective ways to mitigate the effects of future climate change in the context of growing food demand,” Liu adds.
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