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's (CPWF) Basin Focal Projects. 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.
It describes the underlying concepts of water use accounts that provide monthly estimates of major water uses in the study river basins, Ganges being one of them. Starting with rainfall (and in some basins snowfall), the accounts track the partitioning of water into runoff, and evapotranspiration by dryland vegetation.
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 account is dynamic, with a monthly time step, and thus accounts for seasonal and annual variability. The account is a high level, whole-of-basin account: necessarily, it averages or glosses over much detail.
The water-use account is a top-down model based on simple partitioning of rainfall into runoff and infiltration into a generalized surface store. This is done at the catchment level, with no attempt to model the spatial distribution of hydrological processes and storages within a catchment.
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.
This is not a detailed catchment hydrology model, and is not suited to river planning and management, or to investigations of small-scale, detailed effects. It is at a level of detail appropriate to an overview of the uses of water at a river-basin scale. The individual model components are inferred from the data, rather than pre-conceptions.
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