Agriculture Reference
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depicting human impacts such as changes in land and water use; also the impacts of water
storage and depletion through withdrawals for various water uses, and inter basin water
transfers. The model takes into consideration complex interaction between numerous
factors including surface and groundwater, land use and natural water supply, storage and
water withdrawals and returns, through separate water balances for surface and
groundwater as well as an overall water balance.
To support the 'decision making', several scenarios were examined by a multifaceted
hydrologic modeling which brings on board not only the hydrologic cycle, but also
factors that are relevant for irrigated and rainfed agriculture, forestry and desirable flows
in streams for the aquatic ecosystem.
The approach through modelling the entire land and water use of the basin, as
developed, was found to be useful especially for understanding existing as well as future
water availability; also for assessing future water needs under different scenarios, and for
analysing the impact of different policy options for an integrated and sustainable
development of resources. In a dynamic situation, one sees in the developing nations like
India the conversion of barren lands either into forests or into irrigated or rain fed
agriculture. Such actions tend to increase the evapo-transpiration, and in turn impact the
river or stream flows adversely. Similarly, rainwater harvesting and soil and water
conservation practices were also seen to influence the total as well as the inter-
distribution of surface and groundwater. An impact of internal changes in land use
invariably occurs in the long run. The changes in policies and programmes in regard to
soil and water conservation can be properly tested only when the overall water balance
for the entire land phase of the hydrologic cycle is studied. Dry season flow in rivers is
contributed-to by shallow aquifers. Large-scale groundwater use for agriculture is
becoming more common in some basins, particularly in India and Pakistan. Such use
severely affects environmental interests and the sustenance of ecosystems, as the base
flow in rivers vanishes, apart from depletion of the water table. The separate water
accounts for the river-surface and groundwater systems enable a study of this in order to
achieve integration of supply sources and to consider the natural and human-induced
interaction between the surface and groundwater components. Nevertheless, one also sees
that several hydrologic modelling solution techniques are available to study any basin in a
detailed manner; but these are seen to be rigorous, and hence are more apt to evolve the
best operational policies of existing systems that are developed fully. A quick and easier
approach is to study the dynamics of different options where development actions are still
being contemplated, as in India (and other developing countries). The impacts of such
actions were required to help decision-making processes, and CPSP is one such attempt.
India was chosen for the detailed study alongside China, and this paper restricts its
coverage to Indian studies only. Two typical basins were taken up. A water deficit basin
in the west coast, namely the Sabarmati river basin, and a water rich basin in the east
coast, namely the Brahmani river basin, were the candidates for this study. The location
of these basins is shown in the India country map - (Annex Map 1).
For depicting the type of results emerging out of the CPSP, the example of Sabarmati
is dealt with broadly in what follows.
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