Many objective optimization and impact assessment of water management options in the Jaguaribe Basin of North East Brazil

The Jaguaribe river basin in the north east of Brazil lies in the country's driest state, Ceará. Rainfall is concentrated in six months of the year, evapotranspiration can reach 2000 mm per year and a high proportion of the population relies on irrigated agriculture for their subsistence or livelihood. The current water management strategy involves negotiating monthly release rates from each of the basin's three major reservoirs twice a year. The state water management company leads these negotiations with representatives of various water user groups; releases are decided based on the currently stored volume and limited modelling of release scenarios. Presently reservoirs are managed such that municipal demands are guaranteed for 30 months from the date of negotiation. We use multi-objective optimization to search for the pareto-optimal number of months of municipal demand to be guaranteed, and the shape of release rules (based on stored volume). System performance is assessed by comparing flow-duration curves and livelihood factors, such as riparian farm land availability and fishery quality , in addition to the satisfaction of demands in the region supplied by each reservoir. Historical monthly flows are used to simulate the system over 90 years. Results shows the trade-offs between different performance measures and the effects of management option combinations on different water users. A few climate change projections of reservoir inflows are used to assess how a selection of the resulting release rules might perform against the same measures under altered future hydrological conditions. The proposed approach helps planners evaluate the impacts of management options and allows finding balanced stakeholder-backed ways to reduce negative impacts on the environment and the region's vulnerable groups while maintaining overall system performance.