NeStRes – Model for Operation of Non-Strategic Reservoirs for Irrigation in Drylands: Model Description and Application to a Semiarid Basin

Abstract

Water availability in dry inhabited environments has usually been promoted by large strategic reservoirs, but small non-strategic ones, built by farmers and communities, are unable to cope with long term droughts and inappropriate for human supply. Nevertheless, small reservoirs promote water spatial distribution and play a major role for livelihood in rural areas. To fill the gap of operation methods for non-strategic reservoirs used for irrigation where water is a limiting factor, the NeStRes model was developed. The model is composed of three modules: i) hydrological: to define the reliability of water withdrawals from the reservoir; ii) agricultural: to simulate crop production based on water availability; iii) economic: to compute the possible income from irrigated agricultural crops. NeStRes was applied to 91 reservoirs of the semiarid Banabuiu River Basin – BRB, Brazil. The simulations indicated that the maximum income from the cultivation of maize is obtained when the reservoirs are intensely used, drying completely in one to two thirds of the time. Adoption of a fixed reliability level of daily water supply (54%, in the BRB) generates at least 85% of the maximum possible income for all simulated reservoirs. This model application suggests a paradigm change in the operation of small non-strategic reservoirs in drylands: to use water for crop production and save the revenue, instead of saving water, which is susceptible to evaporation. Although high reliability level is desired for human supply by strategic reservoirs, non-strategic ones can be more intensely explored to generate income from irrigated agriculture in drylands.