An assessment of global net irrigation water requirements from various water supply sources to sustain irrigation: rivers and reservoirs (1960–2000 and 2050)

Abstract

Water supply sources for irrigation, such as rivers, reservoirs, and groundwater, are critically important for agricultural productivity. The current rapid increase in irrigation water use threatens sustainable food production. In this study, we estimated the time-varying dependency of the supply of irrigation water from rivers, large reservoirs with a greater than 1.0 km³ storage capacity, medium-size reservoirs with storage capacities ranging from 1.0 km³ to 3.0 Mm³, and non-local non-renewable blue water (NNBW), particularly taking into account variations in irrigation area during the period 1960–2000. We also estimated the future irrigation water requirements from water supply sources in addition to these four sources, using an irrigation area scenario. The net irrigation water requirements from various supply sources were assessed using the global H08 water resources model. The H08 model simulates water requirements on a daily basis at a resolution of 1.0° × 1.0°. We obtained net irrigation water from rivers and medium-size reservoirs, and determined that the NNBW increased continuously from 1960 to 1985, but the net irrigation water from large reservoirs increased only marginally. After 1985, the net irrigation water from rivers approached a critical limit with the continued expansion of the irrigation area. The irrigation water requirements from medium-size reservoirs and NNBW increased significantly following the expansion of the irrigation area and the increased storage capacity of medium-size reservoirs. Under the irrigation area scenario without climate change, global net irrigation water requirements from additional water supply sources will account for 26% of the total requirements in the year 2050. We found that expansion of irrigation areas due to population growth will generate an enormous demand for irrigation water from additional resources

Asian irrigation, African rain: Remote impacts of irrigation

“…Both scenarios fall within the range of estimates from previous studies. IRR max is close to the upper limit of estimates and it is likely that the present irrigation‐induced moisture flux is closer to the one simulated in IRR min [ Gordon et al , ; Wada et al , ; Yoshikawa et al , ]. Nonetheless, it can be seen that the remote impacts are sensitive to the magnitude of the moisture flux related to irrigation.…”

Influence of Groundwater Extraction Costs and Resource Depletion Limits on Simulated Global Nonrenewable Water Withdrawals Over the Twenty‐First Century

“…The first is a clear moderating effect on global groundwater depletion, which brings about a departure from the historically observed linear increase in depletion with demand. Yoshikawa et al () project a doubling of global groundwater depletion rates between years 2000 and 2050. A projected rise in groundwater depletion is also present in Wada and Bierkens (), although the rate of increase is less, with an approximate doubling of current depletion rates by the end of the century (the discrepancy between the two studies is largely due to allowance for increased irrigated land area in the former).…”

“…Spatially varying demands for water are introduced as fixed trajectories, and nonrenewable groundwater is summoned where needed to supply the portion of that demand unmet by renewable water. Perhaps unsurprisingly, the resulting projections of groundwater depletion follow the assumed demands for water, increasing steadily through the century (e.g., Yoshikawa et al, ; Wada & Bierkens, ). But the underlying assumption of a fixed water demand trajectory is problematic, because it neglects the likelihood that users of groundwater will curb their withdrawals as resources draw down.…”

Illustrating a new global-scale approach to estimating potential reduction in fish species richness due to flow alteration

“…FSR calculated by the FSR-FLVAR method were generally more sensitive than those predicted by the FSR-MAD method. For comprehensive future assessments, the impacts of water use and river regulation should be incorporated into this framework, as was done in global-scale water resource models, accounting for the effects of anthropogenic water use and dam regulation (Biemans et al, 2011;Döll et al, 2009;Wada et al, 2011;Wisser et al, 2010;Yoshikawa et al, 2013).…”