Simple water use accounting of Ganges basin - A working paper by Challenge Program on Water and Food

This paper deals with basin water use accounting and is a contribution to the synthesis work of the CGIAR Challenge Program on Water and Food (CPWF) Basin Focal Projects. It applies principles of water use accounts, developed in the first of the series to the Ganges river basin in South Asia. It provides a means to assess the interactions between water, food, poverty, and the environment and helps develop sound information about water availability in a basin, where it goes and how it is used.

The water-use accounts spreadsheets provide basin overviews of water uses, and provide a basis for examining the impact of physical changes to the system and for interactions with agricultural productivity, economics, and livelihoods. More specifically, the paper observes the following -

• The simple spreadsheet model with few adjustable parameters has produced plausible runoff and river flow behavior in the Ganges basin and can be further developed to give a better representation of water use by different land use. 
• Net discharge from the basin accounts for more water than any other use, followed by rainfed agriculture. Irrigation is the third major water user, accounting for a little under a quarter of the total water use: one third of the irrigation water comes from groundwater.
• A unique feature is the strong seasonal variation in both precipitation and potential evaporation. The water related issues in the basin are both due to high and low flow. 
• Net runoff is about 37 % of total precipitation. Rainfed agriculture covers 52 % of the basin and uses about 32 % of the precipitation. Grassland covers much of the upper part of the basin, consuming about 9 % of the precipitation. Irrigated agriculture covers 25 % of the basin and uses about 18 % of the water.
• Changing irrigation efficiency from the currently assumed 40 % to 60 % and increasing the irrigated area by 10 % has relatively little impact on water availability overall since the water thus made available can be consumed downstream.

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