A modeling study of irrigation effects on global surface- and groundwater resources under a changing climate

Tuesday, 16 December 2014
Guoyong Leng1, Maoyi Huang1, Qiuhong Tang2 and L. Ruby Leung1, (1)Pacific NW Nat'l Lab-Atmos Sci, Richland, WA, United States, (2)IGSNRR Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing, China
In this study, we investigate the effects of irrigation on global surface water (SW) and groundwater (GW) resources by performing simulations of the Community Land Model 4.0 (CLM4) at 0.5-degree resolution driven by downscaled/bias-corrected historical climate simulations and future projections from five General Circulation Models (GCMs) from 1950-2099. For each climate scenario, three sets of numerical experiments were configured: (1) a control experiment (CTRL) in which all crops are assumed to be rainfed; (2) an irrigation experiment (IRRIG) in which the irrigation module is activated; and (3) a groundwater pumping experiment (PUMP) in which a groundwater pumping scheme coupled with the irrigation module is activated. The parameters associated with irrigation and groundwater pumping were calibrated based on a global inventory of census-based SW and GW use compiled by the Food and Agricultural Organization (FAO).

Our results suggest that irrigation could lead to two major opposing effects on SW/GW: SW depletion/GW accumulation in regions with irrigation primarily fed by SW, and SW accumulation/GW depletion in regions with irrigation fed primarily by GW. Furthermore, irrigation depending primarily on SW tends to have larger impacts on low-flow than high-flow conditions of SW, suggesting that intensive irrigation water use has the potential to further exacerbate low-flow conditions, increasing vulnerability to drought. By the end of the 21st century (2070-2099), climate change significantly increases (relative to 1971-2000) irrigation water demand in the regions equipped for irrigation across the world. The increase in demand combined with the increased temporal-spatial variability of water supply will cause more severe issues of local water scarcity for irrigation. Regionally, irrigation has the potential to aggravate climate-induced changes of SW/GW although the effects are negligible when averaged globally. Our results emphasize the importance of accounting for irrigation effects and irrigation sources in regional climate change impact assessment.