Comparison of the water footprint of two hydropower plants in the Tocantins River Basin of Brazil

The purpose of this study was to characterize the water footprint of the Tucuruí and Lajeado hydropower plants (HPPs), located in the Tocantins River Basin, Brazil. The water footprint of hydropower was evaluated by three different methods based on the electricity production of the HPP and the monthly and annual evaporation rates estimated according to Penman's method. The first water footprint method (WF-1) considers only the gross water consumption by the HPPs; the second method (WF-2) considers the net water consumption, discounting what would be lost by evapotranspiration in the area previous to the construction of the reservoir; and the third method (WF-3) accounts for the net water balance. The results demonstrated that the estimates of average annual water footprint for the Tucuruí reservoir, using the WF-1, WF-2 and WF-3 methods, were, respectively, 49 m3/GJ, 26 m3/GJ and −21 m3/GJ, while for Lajeado, these estimates were 95 m3/GJ, 48 m3/GJ and 21 m3/GJ. The flooded area of the reservoir per unit of installed capacity of Tucuruí HPP is 34 ha/MW, while for Lajeado, this value reaches 70 ha/MW, which explains Tucuruí's greater water efficiency. Confirming this result, the normalized WFs based on the reservoir area and the installed capacity were approximately 100% higher for the Lajeado HPP than for the Tucuruí HPP through all water footprint methods analyzed. The WF-2 method is the most appropriate to account for the consumption of water directly related to hydroelectric energy generation since it considers the change in evaporation caused by the construction of the reservoir.