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

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 Banabuiú 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.

     

Discussion of “Investigating the Vulnerability of dry-Season Water Supplies to Climate Change: A Case Study of the Gwangdong Reservoir Drought Management System, Korea” by Donghoon Cha; Sangeun Lee; and Heekyung Park

Cha et al. (Water Resources Management, 26(18):4183–4201 2012) improved the method used to measure the vulnerability of a reservoir water supply that arises due to water scarcity in a dry season. Water supply vulnerability is expected to increase due to climate change. The authors showed that the Gwangdong Reservoir Drought Management Model (GRDM2), developed in a previous study and based on the adaptation mechanism, is useful to estimate the vulnerability of water supplies. The authors assumed 48 future scenarios, consisting of a combination of 6 future inflow scenarios and 8 future water requirement scenarios, of the Gwangdong reservoir drought management system. They computed damage cost of water scarcity in dry seasons until the 2050s. Simulation results showed that severe damage may take place from the 2020s and damage four times greater than in the 2009 water scarcity event may occur in the 2050s. As a result, GRDM2 was reported to be useful to measure the magnitude of climate change vulnerability, concentrating on damage of water scarcity in a dry season.