Impacto das mudanças climáticas sobre as vazões em bacias hidrográficas do pampa brasileiro

Abstract

Climate changes have become a growing concern worldwide. These changes have an impact on the management of water resources as they may change hydrological conditions in an uncertain manner in the future. As a consequence, changes in rainfall and temperature spatial and temporal patterns are expected due to changes regimes. Therefore, they can cause significant impacts on the climate of each region, which may affect agriculture, urban and industrial development, and water availability, and increase the frequency of occurrence of extreme events, such as floods and droughts. In this context, the present study aims to assess the impact of climate changes on the hydrological conditions of three subwatersheds of the Mirim-São Gonçalo basin (MSGB). MSGB is characterized by the Pampa biome and is considered an area of environmental, social and economic importance for the southern Brazil. This basin is extremely sensitive to variations in the water regime, thus, studies that consider the simulation of the impacts associated with climate changes in the region are important. The Soil and Water Assessment Tool (SWAT) was calibrated and validated for each subwatershed considering observed meteorological and hydrological data and, later, such a model was forced with daily meteorological data simulated for the past and projected for the future. These projections were based on the Representative Concentration Paths (RCPs) 4.5 and 8.5 of four global climate models by the downscaling projections of the ETA model: Brazilian Earth System Model (BESM), Canadian Earth System Model (CANESM2), Hadley Centre Global Environmental Model (HADGEM2), and Interdisciplinary Research on Climate (MIROC5). In general, the SWAT performance was satisfactory in the calibration and validation for all sub-watersheds, as well as in the representation of the hydrological indicators analyzed in this study. With respect to climate changes, the results indicate an increase in annual average, maximum and minimum streamflows, and that the greatest variations were obtained for the climate projections based on RCP 4.5. For RCP 8.5, most of the hydrological indicators presented an increase that was less accentuated at the end of the 21st century. The results project the effects of climate changes on water availability, where an increase in rainfall in future periods is expected for the region, leading to an increase in streamflows, generating water erosion and a higher frequency of extreme events. On the other hand, these results can be positive for agriculture, which depends heavily on the future water availability. Such results can help decision makers to better structure the management of water resources considering these expected climate and hydrological changes.