The Challenge Program on Water and Food undertakes research to maximize water productivity in several of the world’s major river basins. The research must be underpinned by information on how much water there is in a basin, where it goes and how it is used. There should, furthermore, be an understanding of future constraints (such as the impact of climate change), opportunities (such as increased diversions for irrigation), and trade-offs (such as changed land use improving dryland productivity but leaving less water for downstream use).
We describe the underlying concepts of water use accounts that provide monthly estimates of major water uses in a river basin. We have used them for historical estimates, and they can also be used for prediction. Starting with rainfall (and in some basins snowfall), the accounts track the partitioning of water into runoff, and evapotranspiration by dryland vegetation. The runoff is tracked as it becomes flow down the rivers, with losses (such as evaporation and seepage) and gains (such as tributary inflows), storages in lakes and reservoirs, diversion for irrigation or other purposes, floods in lowland floodplains, and finally discharges to the sea. The account estimates the water use by the major irrigation industries and other uses. The account helps develop understanding of the water uses in a basin, and the likely consequences of large changes, such as climate change, land-use change, increased diversions and irrigation water use, and changed storages.
The water use accounts are developed as Excel spreadsheets. They are a tool for integrated water-resources management, and provide a sound basis for integrating hydrology, environment, social and economic issues, and policy and institutional issues in a river basin.
CPWF Working Paper: Basin Focal Projectseries, BFP01. Colombo, Sri Lanka: The CGIAR Challenge Program on Water and Food. 22 pp.