Water scarcity ahead for 80% of croplands, but farming methods can help

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According to a new study published April 25, 2022, in the peer-reviewed AGU journal Earth’s Future, agricultural water will become scarce in over 80% of the world’s croplands.

The study examines current and future water requirements for global agriculture and predicts whether the water levels available, either from rainwater or irrigation, will be sufficient to meet those needs under climate change. To do so, the researchers developed a new index to measure and predict water scarcity in agriculture’s two major sources. First is soil water that comes from rain, called green water. Second is irrigation from rivers, lakes and groundwater, called blue water. This is the first study to apply this comprehensive index worldwide and predict global blue and green water scarcity as a result of climate change.

Xingcai Liu is an associate professor at the Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences and lead author of the new study. Liu said:

As the largest user of both blue and green water resources, agricultural production is faced with unprecedented challenges. This index enables an assessment of agricultural water scarcity in both rainfed and irrigated croplands in a consistent manner.
Demand for water has grown
In the last 100 years, the 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 fail to take a comprehensive look at both blue and green water.

Green water is often overlooked
Green water is the portion of rainwater available to plants in the soil. A majority of precipitation ends up as green water. It is often overlooked because it is invisible in the soil and can’t be extracted for other uses. The amount of green water available for crops depends on the how much rainfall an area receives and how much water is lost due to runoff and evaporation. Farming practices, vegetation covering the area, the type of soil and the slope of the terrain also have an effect. As temperatures and rainfall patterns shift under climate change, and farming practices intensify to meet the needs of the growing population, the green water available to crops will also likely change.

Mesfin Mekonnen, an assistant professor of Civil, Construction and Environmental Engineering at the University of Alabama who was not involved in the study, said the work is:

… very timely in underlining the impact of climate on water availability on crop areas. What makes the paper interesting is developing a water scarcity indicator taking into account both blue water and green water. Most studies focus on blue water resources alone, giving little consideration to the green water.
Water scarcity in the future
The researchers find that under climate change, global agricultural water scarcity will worsen in up to 84% of croplands. They say there will also be a loss of water supplies driving scarcity in about 60% of those croplands.

If greenhouse gas emissions rise, experts predict that agricultural water scarcity will intensify in 84% of croplands from 2026 to 2050. In this figure, dark brown hues indicate greater water scarcity. Image via Liu et al./ Earth’s Future.
Sowing solutions help water scarcity
Experts expect changes in available green water, due to shifting precipitation patterns and evaporation caused by higher temperatures, to impact about 16% of global croplands. Adding this important dimension to our understanding of water scarcity has implications for smarter agricultural water management.

For example, scientists predict northeast China and the Sahel in Africa 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 new index helps countries assess the threat and causes of agricultural water scarcity to develop strategies to reduce future droughts.

Multiple practices help conserve agricultural water. Mulching reduces evaporation from the soil. No-till farming encourages water to infiltrate the ground. Adjusting the timing of plantings better aligns crop growth with changing rainfall patterns. Additionally, contour farming, where farmers till the soil on sloped land in rows, prevents water runoff and soil erosion.