Water Scarcity Expected to Worsen More than 80% of Croplands Globally

According to a new study published in the AGU journal Earth's Future, agricultural water scarcity is expected to increase in more than 80% of the world's croplands by 2050. The study looks at current and future water needs for global agriculture and predicts whether available water sources, such as rainwater or irrigation, will be enough to meet those needs as climate change occurs.

Findings of Study:

To do so, the researchers created a new index to measure and predict water scarcity in agriculture's two major sources: rain-fed soil water (green water) and irrigation water (blue water) from rivers, lakes, and groundwater. It's the first study to use this comprehensive index globally to forecast global blue and green water scarcity due to climate change.

"Agricultural production faces unprecedented challenges as the largest user of both blue and green water resources," said Xingcai Liu, an associate professor at the Chinese Academy of Sciences' Institute of Geographic Sciences and Natural Resources Research and the lead author of the new study. "This index allows for a consistent assessment of agricultural water scarcity in both rainfed and irrigated croplands."

Water demand has increased twice as fast as the human population over the last century. Water scarcity is already a problem in agriculture on every continent, posing a serious threat to food security. Despite this, most water scarcity models have failed to include both blue and green water in their analyses.

The portion of rainwater that is available to plants in the soil is known as green water. Green water makes up the majority of precipitation, but it is often overlooked because it is invisible in the soil and cannot be extracted for other purposes. The amount of green water available for crops is determined by the amount of rainfall received and the amount of water lost through runoff and evaporation.

Farming practices, vegetation cover, soil type, and slope of the terrain can all influence the outcome. The green water available to crops will likely change as temperatures and rainfall patterns shift due to climate change, and farming practices intensify to meet the needs of a growing population.

Mesfin Mekonnen, an assistant professor of Civil, Construction, and Environmental Engineering at the University of Alabama who was not involved in the research said the findings are "very timely in emphasizing the impact of climate on crop water availability."

"What interests me about the paper is the development of a water scarcity indicator that considers both blue and green water," he said. "Most studies concentrate solely on blue water resources, with little regard for green water."

According to the researchers, global agricultural water scarcity will worsen in up to 84 percent of croplands as a result of climate change, with a loss of water supplies driving scarcity in about 60% of those croplands.

Changes in available green water as a result of shifting precipitation patterns and increased evaporation due to higher temperatures are expected to affect about 16 percent of global croplands. Including this crucial dimension in our understanding of water scarcity may have implications for agricultural water management. More rain is expected in Northeast China and the Sahel region of Africa, for example, which could help alleviate agricultural water scarcity. Reduced precipitation in the Midwest and Northwest India, on the other hand, may lead to increased irrigation to support intensive farming.

The new index could aid countries in assessing the threat and causes of agricultural water scarcity, as well as developing strategies to mitigate future droughts.

Several practices aid in agricultural water conservation. Mulching reduces soil evaporation, no-till farming encourages water infiltration, and planting at different times can better align crop growth with changing rainfall patterns. Furthermore, contour farming, in which farmers till the soil in rows of the same elevation on sloped land, prevents water runoff and soil erosion.

"In the long run, improving irrigation infrastructure and irrigation efficiency, for example in Africa," Liu said, "would be effective ways to mitigate the effects of future climate change in the context of growing food demand."

(Source: American Geophysical Union)