Distributed ecohydrological modelling to evaluate the performance of irrigation system in Sirsa district, India I. Current water management and its productivity

Distributed ecohydrological modelling can provide a useful tool to evaluate the performance of irrigation systems at different spatial and temporal scales. Sirsa district, covering 4270 km2 in the western part of Haryana State (India), has been selected for a case study with typical problems of canal water scarcity, poor groundwater quality, rising and declining groundwater levels, and sub-optimal crop production. The field scale ecohydrological model SWAP including detailed crop growth simulations was extended in a distributed manner to quantify the required hydrological and biophysical variables for all combinations of weatherââ"šÂ¬Ã¢â‚¬Å“cropââ"šÂ¬Ã¢â‚¬Å“soilââ"šÂ¬Ã¢â‚¬Å“irrigation in the study area. Field experiments, satellite images and existing geographical data were used to aggregate the representative input parameters of all so-called homogeneous ââ"šÂ¬Ã‹Å“simulation unitsââ"šÂ¬Ã¢"žÂ¢ and their boundary conditions. The simulated mean annual evapotranspiration (689 mm) over the entire Sirsa district was 15% lower as compared to the mean annual evapotranspiration (809 mm) estimated by independent remote sensing approach. The simulated water and salt limited crop yields showed a good correspondence with the independent crop yields data obtained from remote sensing, field measurements and statistical records. The performance of Sirsa district during the agricultural year 2001ââ"šÂ¬Ã¢â‚¬Å“2002 was evaluated in terms of water productivity, net groundwater recharge and salt build-up. Factors responsible for low water productivity in Sirsa district include a high percentage of soil evaporation into evapotranspiration (17ââ"šÂ¬Ã¢â‚¬Å“54%, highest for rice), percolation from fields and seepage losses from the conveyance system (34ââ"šÂ¬Ã¢â‚¬Å“43% of the total canal inflow). The study also revealed a large variation of net groundwater recharge and salt build-up over different canal commands, which threatens the sustainability of irrigated agriculture in Sirsa district.