Water Debt Indicator Reveals Where Agricultural Water Use Exceeds Sustainable Levels

Abstract

Agriculture overexploits water resources in many regions, as water stress metrics highlight. Tracing back the causes of water overuses and separately accounting for soil water, surface water and groundwater resources is an open challenge to monitor the sustainability of agricultural water use. We introduce the “water debt repayment time” indicator, measuring the time required to replenish water resources used for annual crop production. This indicator disentangles source‐ and crop‐specific water overuses at a high spatial resolution. Globally, we find that wheat and rice production critically overuses groundwater resources and cotton production overuses both surface water and groundwater. Locally, unsustainable production is found over the Sabarmati Basin and in the Chao Phraya Basin, where the repayment time exceeds 5 years in many cultivated areas. Critical overuses are also found over the High Plain and Indo‐Gangetic Plains, where the repayment times reach 50 years. Unsustainable irrigation is often a consequence of growing crops during local dry seasons.

Unsustainable groundwater use for global food production and related international trade

“…They introduced the concept of the groundwater footprint, defined as the area-averaged ratio of abstraction to recharge (where the contribution to environmental streamflow is first deduced from the recharge), with data sources and models similar to those used by Wada et al (2010) (i.e., PCR-GLOBW and national groundwater use statistics). Tuninetti et al (2019) introduced the crop-specific ‘water debt’ indicator, comparing crop water use to availability of green, surface water and groundwater resources from grid cell to watershed and at a national scale.…”

Water, energy and land insecurity in global supply chains

“…The impact of human activity across the Water-Energy-Land (WEL) system is unprecedented within history (Steffen et al, 2015). Major water basins have been over-exploited (Wang and Zimmerman, 2016), some at fifty times their replenishment rate (Tuninetti et al, 2019), resulting in an estimated four billion people affected by severe water scarcity (Mekonnen and Hoekstra, 2016). Global energy demand, primarily for fossil fuel resources, has brought humanity dangerously close to tipping points in the climate system whilst also curtailing national security (Andrews-Speed et al, 2012;IPCC, 2014).…”

Trade of Economically and Physically Scarce Virtual Water

“…On the other hand, other authors identify some paradoxes since some water-scarce countries or areas actually are net VW exporters, and vice versa [13,14,54,55,56]. A second group of scholars focuses on whether VW fluxes associated to agricultural products are 'sustainable' from an environmental point of view, providing different estimates of water stress due to VW trade [among others 11,15,16,17,18,19,20,21,49]. However, only physical water availability is typically considered in both viewpoints when the water endowment of a country is assessed, i.e.…”