Non-uniform irrigation affects groundwater recharge and nitrate leaching

What is it about?

In semi-arid regions like Colorado, USA, agricultural water has high value as municipalities seek water security under growing populations and projected climate change and variability. Historical “return flows” to streams and groundwater must be subtracted from the amount of irrigation water traded. A framework for simulating spatially variable infiltration and derived distributions of groundwater recharge and nitrate leaching is defined and demonstrated. We used an agricultural system model to simulate groundwater recharge and nitrate leaching under irrigated corn in Colorado, USA. Projected climate representing a period centered on 2050 increased baseline recharge by up to 58%, but the climate effect decreased with increasing spatial variability of applied irrigation. This study illustrates a framework for further evaluations of the potential combined effects of irrigation management and climate change on groundwater resources.

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Photo by henry perks on Unsplash

Photo by henry perks on Unsplash

Why is it important?

Temporal averaging of fluxes over a sufficient time period can provide well-defined transfer functions to convert variable inputs (irrigation) to the output fluxes of interest. Irrigation “return flows” to groundwater (renewable “blue” water) respond nonlinearly to irrigation (in)efficiency. The derived distribution approach allows distributional uncertainty of irrigation efficiency (spatial variability) to be translated to output distributions and mean fluxes over space and time. The current simulations of climate change showed potential for large increases (32 to 58%) in recharge (2050 versus historical climate). The water footprint of cropping systems can be estimated along with the combined return flow to groundwater available for future pumping. Such analyses may require complex systems models and should not be oversimplified.

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