Basin-Wide Water Accounting Using Remote Sensing Data: The Case of Transboundary Indus Basin
The paper describes the application of a new Water Accounting Plus (WA+) framework to produce spatial information on water flows, sinks, uses, storages and assets, in the Indus Basin, South Asia. It demonstrates how satellite-derived estimates of land use, land cover, rainfall, evaporation (E), transpiration (T), interception (I) and biomass production can be used in the context of WA+. The results for one selected year showed that total annual water depletion in the basin (502 km3) plus outflows (21 km3) exceeded total precipitation (482 km3). The deficit in supply was augmented through abstractions beyond actual capacity, mainly from groundwater storage (30 km3). The "landscape ET" (depletion directly from rainfall) was 344 km3 (69% of total consumption). "Blue water" depletion ("utilized flow") was 158 km3 (31%). Agriculture was the biggest water consumer and accounted for 59% of the total depletion (297 km3), of which 85% (254 km3) was through irrigated agriculture and the remaining 15% (44 km3) through rainfed systems. While the estimated basin irrigation efficiency was 0.84, due to excessive evaporative losses in agricultural areas, half of all water consumption in the basin was non-beneficial. Average rainfed crop yields were 0.9 t ha−1 and 7.8 t ha−1 for two irrigated crop growing seasons combined. Water productivity was low due to a lack of proper agronomical practices and poor farm water management. The paper concludes that the opportunity for a food-secured and sustainable future for the Indus Basin lies in focusing on reducing soil evaporation. Results of future scenario analyses suggest that by implementing techniques to convert soil evaporation to crop transpiration will not only increase production but can also result in significant water savings that would ease the pressure on the fast declining storage.