Towards a framework for quantifying water resources in india
D. Shankar
e-mail: shankar@darya.nio.org
Vidya Kotamraju
e-mail:vidyakr@darya.nio.org
S. R. Shetye
Physical Oceanography Division, National Institute of Oceanography
Dona Paula, Goa 403004, India.
Abstract
While issues related to water attract considerable attention in India, very little quantitative information is available on her water budget. There are two reasons for this lacuna: the dearth of information on hydrological variables, and the absence of an easily accessible quantitative framework to put these variables in perspective. In this paper, we assemble a framework to address both issues. At its core is a hydrological routing model; the basic data needed for implementing the framework are a digital elevation model and data on precipitation and evapotranspiration. We demonstrate the viability of the framework by applying it to the hydrology of the Mandovi river in Goa. The model output mimics the observed discharge well.
Introduction
India, as one of the countries affected by both population explosion and the Green Revolution, hardly sees a day without some problem related to water figuring in the news. The problems are twofold (Agarwal and Narain, 1997, 1999; Agarwal and Chak, 1991; Agarwal et al., 1999; Rao, 1975). First, there is the problem of scarcity, resulting in drought or famine; second, there is the problem of surplus (mostly during the summer monsoon, when most of India receives almost 80% of the annual precipitation), resulting in floods. It is also evident that certain regions of the country, especially in the south and northwest, are more prone to drought, while other regions, especially in the east and northeast, are more prone to floods. With each disaster comes the clamour for some long-term solution. One solution that has been proposed is the transfer of water, through the medium of a network of canals, from river basins with a surplus (mostly the rivers in the north and northeast) to river basins with a deficiency (Radhakrishna, 2003; Rao, 1975) (mostly in the south and northwest). This idea received a major boost last year following one of the worst droughts of the century (Gadgil et al., 2002).
The financial implications of networking rivers over an area the size of India are enormous: a tentative estimate for this project is Rs. 560000 crores (Radhakrishna, 2003). Commissioning a project of such magnitude and then executing it successfully will require a vast database on hydrology and a framework that can use the data to quantify the water budget for each river basin. This apart, given the pressure that exists on the resources of fresh water, there is an urgent need to evolve better, sustainable strategies for managing the country's water resources. This, in turn, requires hard data on the basis of which decisions can be made: we need quantitative estimates of water budgets for the river basins at a resolution small enough for evolving strategies for, say, an average Indian district, yet large enough to make possible an estimate of water resources on the scale of the Indian subcontinent.
The estimates of water resources available in India today are often on too small a scale, like a small watershed, or are on too large a scale, like gross statistics based on the average precipitation over the entire country and the measurements made at a few stream-flow gauges on major rivers and in the neighbourhood of some dams (Nag and Kathpalia, 1975; Agarwal and Narain, 1999; Anon, 1988; Rao and Ramaseshan, 1985; Chaturvedi, 1985; Rao et al., 1971; Rao, 1975). For individual river basins, the tendency has been to adopt an empirical systems
approach (Chaturvedi and Srivastava, 1981; Rao, 1975). What is lacking is an overview that provides a reliable quantitative estimate of the water resources of the country. There are two reasons for the absence of such estimates. First, there is a dearth of information on the basic hydrological variables of interest -- groundwater recharge rates, stream-flow, evapotranspiration, etc. Only precipitation data have been collected systematically over a long period; evapotranspiration data are scanty (Rao, 2001); stream-flow data are confined to a few rivers, and are often not easily accessible (The Ad Hoc Group on Global Water Data Sets, International Association of Hydrological Sciences, 2001; Radhakrishna, 2003). Second, a quantitative framework that can put these variables in perspective is often missing. Though several hydrological software packages are available, Indian academic institutions are reluctant to invest in them because these packages are usually expensive and are geared to handle situations in developed countries where the hydrological databases are much more advanced. They also rely too often on commercial GIS (Geographical Information Systems) packages, which too are expensive for Indian academic institutions. Hence, in view of the present state of continental-scale hydrology of the subcontinent, it seems that what is needed today is a quantitative framework that satisfies the following conditions.
- The framework should include a simple hydrological model that can provide a reliable water balance of a river system;
- demands on the database required by the model should be consistent with the realities in the country;
- the packages that incorporate the model should be able to handle a range of spatial scales, from small rivers to continental scales, to enable many groups working independently on different river basins to dovetail their analyses into a coherent picture on the larger scale; and
- the models and their ancillary software should be freely accessible.