Pegada hídrica das usinas hidrelétricas do sistema interligado nacional na região hidrográfica do Paraná

Abstract

Recently, water footprint (WF) has been used as an indicator of the efficiency and sustainability of water resources assigned for hydropower generation. WF of a given hydropower plant is calculated based on the ration between evaporation from the reservoir and the electric energy generated by the facility, and it is known as Gross Water Footprint (GWF); however, WF can also be calculated taking into account the net evaporation, a so-called Net Water Footprint (NWF). This study was carried out at Funil Hydropower Plant (FHP), located in Grande river, southern Minas Gerais, Brazil, using observed weather datasets of two consecutive years, recorded by four meteorological stations installed in the reservoir’s surroundings. It was possible to analyze the intra-annual WF behavior of this facility along with the use of this indicator. In addition, a spatial and temporal wider study was also conducted based on operative data of the plants and weather data over a period of fifteen years for the Parana Hydrograph region (PHR), which accounts 62 hydropower plants belongs to the Brazilian Interconnected System (SIN). This second study was done considering each one plant and in a systemic way for entire PHR. GWF and NWF to FHP was, respectively, equal to 29 and 13 m 3 .GJ -1 , being the later 55% lower. This difference occurred due to the methodology approaches considered in the calculation of GWF and NWF; the later one considers the difference between the evapotranspiration from the flooded area before the reservoir filling and the evaporation from it. The results have demonstrated a reasonable efficiency of the water use for electric energy generation in FHP, since both WFs are low, allowing for characterizing a positive balance between water availability and water demand in the basin where the plant is located. The hydropower plants belonging to the SIN have showed different behaviors for WF especially due to the specificities of each one facility, e.g. installed power, energy generation, and size of the reservoirs. In this sense, WF showed low correlation with both Köppen climate type and the reservoir evaporation, however, a strong dependence of the flooded area and installed power ration (ha.MW-1 ) was observed. Power plants built with a water constant reservoir level showed lower WF than the plants built with reservoirs of regularization (non-constant level), mainly those located in the headwater basins. GWF and NWF of the electric energy generation from PHR were, respectively, of 25 and 11 m 3.GJ -1 , meaning that the most important hydrograph region in the context of hydroelectric generation in Brazil is, on average, lower than the WF observed in other Brazilian facilities or even in the world. Itaipu Power Plant stands out being the second greatest facility in world in terms of installed power and the greatest in the energy production, which leaded to lower WF. Considering now the basins of the PHR as reference, Iguassu Basin showed the lowest WF (from 7 to 1,6 m3 .GJ -1 , respectively, for GWF and NWF) because of the highest installed power and small reservoirs which generated the lowest amount of evaporation. In the other hand, Tiete river basin showed the largest WF among the basins of the PHR (120 and 61 m 3 .GJ -1 , respectively, for GWF and NWF) due to the lowest installed power in relation to the flooded area of the SIN reservoirs in this basin.