Improving allocation of irrigation water in southwest India

Irrigation schemes in southwest India are heterogeneous in crops, area of irrigation units, soils and climate. The areas planned for irrigation each year under different crops and the scheduled duration of irrigation to each farmer are estimated, however, based on assumed uniform characteristics (planned schedule). In practice the schedules are not followed and users mostly over-irrigate their fields (the actual schedule). In this paper a simulation-optimisation model is used to develop two alternative (proposed) schedules based on full irrigation and on optimised deficit irrigation within the framework of area-proportionate water distribution, taking heterogeneity into account. As a case study, the allocation and water delivery plans were obtained for one irrigation scheme for the actual, planned and proposed schedules and compared using the simulation-optimisation technique. This showed that the proposed schedule for deficit irrigation had the maximum monetary productivity (total net benefits) and area productivity (irrigated area) and that the equity of both proposed schedules was much higher than those for either the planned or actual schedules. The proposed schedules can be adopted within the framework of the existing system of water distribution, which shows that there is considerable scope for improvement in the performance of existing irrigation schemes without major capital investment.