O custo da garantia da água bruta: o caso dos rios intermitentes do Ceará

Abstract

The hydrology of Brazilian Semi-Arid has as characteristics: the intermittency of a number of rivers, the high variability of the annual river discharges, and an intense evaporation. The intermittency of the rivers makes surface reservoirs as the main, and sometimes the unique, way to guarantee water supply. The high stream flow variability makes necessary to keep water stored for long time waiting for a drought that, for sure, will come. In turn, the intense evaporation in water stored results in low efficiency of reservoirs. Some authors consider these inevitable losses as inefficiency of the water management, when, in fact, that is a price to pay for the guarantee of the water supply. The Monte Carlo Method was used to estimate the yield at equilibrium state. In the article the cost of water was estimated in a sample of 40 reservoirs in Ceará State. It was observed that for 99% guarantee the cost of water are 203% more expensive than the cost for 80% guarantee. It was also observed that the cost of water yield can be up to 35 times more expensive in inefficient reservoirs than in the most efficient.