Impact of irrigation on crop yield gain under future change in water resources

Irrigation system has greatly contributed to stable production of crop by alleviating agricultural drought damage, which has been regarded an effective agricultural adaptation measure in response to climate change. Future change in water availability with shifting to a different climate condition is likely to bring a different benefit of irrigation adaptation than current. However, many agricultural impact assessments have not necessarily considered changes in the water availability for irrigation under changing climate. Therefore, we assessed crop yield gains due to irrigation as the benefit of irrigation adaptation under current irrigation system within the context of climate change by using a large-scale crop-river model, CROVER [Okada et al. 2018]. The CROVER model simulates the large-scale terrestrial hydrological cycle and crop growth depending on climate, soil properties, landuse, crop cultivation management, socio-economic water demand, and reservoir operation management. The bias-corrected multi-GCMs outputs under RCP 2.6, 4.5, 6.0, and 8.5 scenarios were used. The grid-cell extents of rainfed and irrigated areas for the individual crops were obtained from MIRCA2000 [Portmann et al. 2010]. The results showed that the global irrigation adaptation benefits on maize yield will decrease with the more distant future or the higher emission scenario. Especially, the decrease is remarkable on the region from Indus River basin to eastern Europe and central North America. For rice also, the irrigation adaptation benefits on Asia are anticipated to decrease with the more distant future or the higher emission scenario. The decrease is significant on Southeast Asia and South Asia, whereas the change of the irrigation adaptation benefits on East Asia differs depending on the GCM. The study found that future change of precipitation condition strongly influences the benefits of irrigation adaptation for crop production.