Modeling water use from non-strategic reservoirs for irrigation of annual crops in the Brazilian semi-arid region

Abstract In the semi-arid region of northeastern Brazil, irregular rainfall, high evaporation rates, and frequent droughts make water supply highly vulnerable. Water provision depends on networks of reservoirs constructed by public authorities and civil society. However, most small reservoirs do not ensure continuous supply and often dry out. In this context, the NeStRes model was developed to define irrigation conditions for temporary crops using non-strategic reservoirs, aiming to maximize irrigator income. The model was applied to 23 reservoirs in the Fogareiro Reservoir basin, Ceará, considering crops such as rice, sweet potato, beans, maize, and sorghum. Key input parameters included crop water demand, crop cycle duration, root zone depth, crop coefficient, production cost per hectare, and market price. Results indicate that the water use that maximizes agricultural income and optimal economic return vary according to reservoir characteristics, geometry, climatic conditions, and crop type. Annual crops are more suitable for non-strategic reservoirs that frequently dry out, as they reduce losses associated with water deficit. However, the main limitation is related to management, since the methodology does not account for multiple water uses and is therefore recommended exclusively for irrigation planning.