Irrigation variability and climate change affect derived distributions of simulated water recharge and nitrate leaching

Authors: Green, Timothy; Anapalli, Saseendran

Submitted to: Water International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2018
Publication Date: 10/15/2018
Citation: Green, T.R., Anapalli, S.S. 2018. Irrigation variability and climate change affect derived distributions of simulated water recharge and nitrate leaching. Water International. 43:829-845. https://doi.org/10.1080/02508060.2018.1515568.
DOI: https://doi.org/10.1080/02508060.2018.1515568

Interpretive Summary: 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.

Technical Abstract: In arid and semi-arid regions, irrigation (“blue”) water used from agriculture has high value as municipalities seek water security under growing populations and projected climate change and variability. In Colorado, USA, water law considers historical return flows to streams and groundwater part of regional water resources which must be quantified before selling water rights. Such return flows are challenging to estimate due to spatial variability of applied irrigation water caused by inefficiency of in-field irrigation application. Here, we define and demonstrate a framework for simulating spatially variable infiltration and derived spatial distributions of deep percolation (i.e., vertical water flux beneath the root zone; called “recharge” here) and nitrate leaching. We used an agricultural systems and vadose zone model, RZWQM2, to simulate recharge and nitrate leaching at a depth of 3 m under irrigated corn (maize; Zea mays L.) in semi-arid northeastern Colorado, USA. Historical and projected climate scenarios were used to evaluate potential changes in simulated groundwater return flows. Predicted average fluxes of the derived distributions indicated moderate increases in historical recharge (2-42%) as the spatial variability of applied irrigation increased. Projected climate representing a period centered on 2050 increased recharge above baseline historical rates by up to 58%, but the climate effect decreased with increasing irrigation inefficiency. Absolute changes in nitrate leaching and surface runoff were small, but negative. This study illustrates a framework for further evaluations of the potential combined effects of irrigation management and climate change on groundwater resources.