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How much water flows into agricultural irrigation? New study provides 18-year water use record

Irrigation for agriculture is the largest use of fresh water around the globe, but precise records and maps of when and where water is applied by farmers are difficult to locate. Now a team of researchers has discovered how to track water used in agriculture.

In a paper published in the journal Geophysical Research Letters, the researchers detail their use of satellite images to produce annual maps of irrigation. The findings, the scientists said, will help farmers, water resource managers and others understand agricultural irrigation choices and make better water management decisions.

"We want to know how human activities are having an impact on the environment," said hydrogeologist David Hyndman of Michigan State University (MSU), principal investigator of the project. "Irrigation nearly doubles crop yields and increases farmer incomes, but unsustainable water use for irrigation is resulting in depletion of groundwater aquifers around the world. The question is: 'How can we best use water?'"

The paper highlights the need to know when and where irrigation is occurring to effectively manage water resources.

The project focuses on an economically important agricultural region of the central U.S.--the Republican River Basin--that overlies portions of Colorado, Nebraska and Kansas, and provides surface water and groundwater to the High Plains Aquifer. The team found that irrigation in this area roughly doubled between 2002 and 2016.

From the study:

Irrigated agriculture is the world's largest consumer of global freshwater. In order to effectively use limited water supplies, managers need to understand when and where irrigation occurs. We fill this knowledge gap by using satellite images to produce annual maps of irrigation for 1999–2016 in a large, economically important agricultural region in the central United States that must manage its water supply for multiple users. We then used these maps to study changes in irrigation over time. We were surprised to find that the total area and individual locations of irrigated fields changed substantially from year to year. Our analysis suggests that farmers expanded irrigation when crop prices were high to increase crop yield and profit. We initially expected to also see increases in drought years to compensate for lack of rainfall, but instead, we found the opposite: irrigated area decreased in dry years. Looking closer, we realized that this happened because farmers had to irrigate more heavily over each field, which reduced the number of fields they could irrigate due to limited water supply. These irrigation maps consistently track irrigation over time and are freely available for others to use to help manage water sustainably and meet food needs.

About:The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2017, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards.