Since the 2nd WWF held at The Hague in 2000 the necessity of curtailing water withdrawals for irrigation purposes and diverting them to nature/ecosystems has been debated. The International Commission on Irrigation and Drainage (ICID) adopted a ''Strategy for Action'' in the same year, highlighting the need for integration of supply and demand sides for the three sectors, viz. food, people and nature. ICID, through its project entitled the Country Policy Support Programme* (CPSP), has carried out a detailed assessment of the water supply-demand situation for the three sectors in two representative river basins each in China and India. The CPSP specifically addresses future water scenarios for food and rural development, water for people as also water for nature, in an attempt to integrate them in the broader context of Integrated water resources development and management (IWRDM) to achieve sustainable development, management and use of the water resources.
The goal of the CPSP is to evolve policy level interventions through the assessments for the representative basins, quantifying and integrating the needs of the three sectors, viz. people, food and nature, on one hand and taking a holistic view of water availability as modified by human interventions on the other.
A hydrologic model has been developed for the basin level assessments which was applied in the two selected basins in India, viz. the Sabarmati and Brahmani. The model enables: (i) simulation of past, present and future conditions of water supply and demand; (ii) quantification of evaporation/evapotranspiration (non-beneficial and beneficial) by the three sectors; (iii) estimation of impact of land-use changes on yields of water in rivers, aquifers, etc.; (iv) computing separate and composite water balances for surface and groundwater systems; (v) simulating interaction between surface and groundwater availability and withdrawal; and (vi) simulating effects of land-use changes on supplies, and impact of sectoral policies.
The Sabarmati river basin has a catchment area of about 2.1 million hectares (Mha) and is a water-deficit basin having intensive agriculture and industrial development and large population density. The current population in the basin is 11.74 million with 51% of the population living in urban areas. Average annual rainfall in the basin is 750 mm with renewable water resources of 4849 million m 3 (Mm 3 ) per year and water availability of 413 m 3 per capita per year. Out of 1.5 Mha of gross cropped area in the basin, about 0.8 Mha (gross) is irrigated. Almost 70% of the current irrigation use is from groundwater. The current storage capacity of the basin is 1324 Mm 3 . Currently about 1580 Mm 3 is imported from the adjacent Mahi river and there is a plan to import up to 2138 Mm 3 of water from the Narmada river to meet the current gap in demand and future demands from expansion of the irrigated area and domestic and industrial water requirements.
The preliminary findings of the application of the model in the Sabarmati basin are as follows:
Non-beneficial evapotranspiration (ET) in the nature and agriculture sectors exceeds annual river flow. A possible strategy to reduce non-beneficial ET could be through rain harvesting and soil and water management measures. Import of the Narmada water is necessary to sustain the present withdrawals and meet future needs, including improvement of low flows. Present groundwater use is unsustainable. While the situation would improve slightly in future due to large additional Narmada imports, composition of return flow indicates a much higher risk of pollution.
The Brahmani basin has a catchment area of about 3.93 Mha and is a relatively water-rich basin, having large industrial development and less developed agriculture. The current population in the basin is 8.46 million of which about 15% is urban. The average annual rainfall of the basin is 1304 Mm with annual renewable water resources of