Abstract
Global water use for food production needs to be reduced to remain
within planetary boundaries, yet the financial feasibility of crucial
measures to reduce water use is poorly quantified. Here, we introduce a
novel method to compare the costs of water conservation measures with
the added value that reallocation of water savings might generate if
used for expansion of irrigation. Based on detailed water accounting
through the use of a high-resolution hydrology-crop model, we modify the
traditional cost curve approach with an improved estimation of demand,
increasing marginal cost per water conservation measure combination and
add a correction to control for impacts on downstream water
availability. We apply the method to three major river basins in the
Indo-Gangetic plain (Indus, Ganges and Brahmaputra), a major global food
producing region but increasingly water stressed. Our analysis shows
that at basin level only about 10% (Brahmaputra) to just over 20%
(Indus and Ganges) of potential water savings would be realised; the
equilibrium price for water is too low to make the majority of water
conservation measures cost effective. The associated expansion of
irrigated area is moderate, about 7% in the Indus basin, 5% in the
Ganges and negligible in the Brahmaputra, but farmers’ gross profit
increases more substantially, by 11%. Increasing the volumetric cost of
irrigation water influences supply and demand in a similar way and has
little influence on water reallocation. Controlling for the impact on
return flows is important and more than halves the amount of water
available for reallocation.