The global value of water in agriculture

Abstract

Major environmental functions and human needs critically depend on water. In regions of the world affected by water scarcity economic activities can be constrained by water availability, leading to competition both among sectors and between human uses and environmental needs. While the commodification of water remains a contentious political issue, the valuation of this natural resource is sometime viewed as a strategy to avoid water waste. Likewise, water markets have been invoked as a mechanism to allocate water to economically most efficient uses. The value of water, however, remains difficult to estimate because water markets and market prices exist only in few regions of the world. Despite numerous attempts at estimating the value of water in the absence of markets (i.e., the "shadow price"), a global spatially explicit assessment of the value of water in agriculture is still missing. Here we propose a data-parsimonious biophysical framework to determine the value generated by water in irrigated agriculture and highlight its global spatiotemporal patterns. We find that in much of the world the actual crop distribution does not maximize agricultural water value.

Keywords: irrigation; water productivity; water value.

Fig. 1.

Current irrigation water value (ca. year 2000, mean value) by region for four major staple crops accounting for 57% of global food calorie and 61% of global protein production for human consumption (36). (A) Values based on water withdrawals to meet irrigation water requirements with the existing technology (Methods). (B) Values based on water consumption (i.e., evapotranspiration) to meet irrigation water requirements. See SI Appendix, Fig. S1 for the definition of these geographic regions.

Fig. 2.

Current (ca. year 2000) value of irrigation water used for irrigation of maize, wheat, soybean, and rice, based on water withdrawals.

Fig. 3.

Crop-specific irrigation water values. The box plots represent current (ca. year 2000) median, 25th, and 75th percentile and maximum and minimum values; outliers are not shown in the figure. These values are based on water withdrawals to meet irrigation water requirements with the existing technology (Methods). See SI Appendix, Fig. S3 for values based on water consumption.

Fig. 4.

Irrigation water value (mean value) considering current (ca. year 2000) crop distribution and the hypothetical distribution of crops that maximize the economic value of irrigation water (i.e., maximize water value; see Fig. 5). These water values are based on estimates of water withdrawals for irrigation. (A) Mean regional water values. (B) Global statistics of irrigation water values. The box plots represent median, 25th, and 75th quartiles and maximum and minimum values; outliers are not shown in the figure. See SI Appendix, Fig. S1 for the definition of these geographic regions.

Fig. 5.

Value of irrigation water withdrawals (A) based on the existing (ca. year 2000) crop distribution and (B) based on the crop that maximizes the value of irrigation water. SI Appendix, Fig. S2 for the correspondent crops that maximize the value of irrigation water. The corresponding values of irrigation water consumption are shown in SI Appendix, Fig. S4.

Fig. 6.

(A) Value of irrigation water (based on withdrawals) in areas suitable for sustainable and unsustainable irrigation (based on existing crop distribution and irrigated areas). In the areas suitable for sustainable irrigation the water value has a more skewed tail toward higher irrigation water values. Sustainable and unsustainable irrigation areas were taken from Rosa (14). (B) Changes in the value of water between 1992 and 2016 as a result of interannual fluctuations in irrigation water demand, water availability, crop yields, and crop prices at the farm gate.