Impacto das mudanças climáticas na qualidade da água na bacia do rio Piracicaba/MG

Abstract

Precipitation and air temperature are the most used variables to indicate the climate changes that are taking place in a given region. The Piracicaba River basin is inserted in an important economic region of the Minas Gerais State, with a strong presence of mining, steel and pulp activities, which depend on water resources in their production processes. In this context, the present study evaluated the influence of air temperature and precipitation on water quality in a current and future scenario in the Piracicaba/MG river basin. For this, water quality parameters dataset was analyzed from 2001 to 2020 and simulated precipitation and temperature data, from the regionalized climate model ETA/HADGEM2-ES, were obtained for 1960 to 2099 period, considering the historical scenario and the one with the greatest increase in the concentration of greenhouse gases. A cross-correlation analysis was performed between all variables and a multiple regression model was adjusted, in order to identify which water quality parameters are most influenced by precipitation and air temperature in the basin. The impact of extreme precipitation and temperature events on water quality was also assessed. According to the results obtained, it was possible to verify that, in a future scenario, air temperature will increase in average by up to 6.6°C by 2099 and precipitation will decrease by up to 3.39 mm/month. The results also showed that, in a warmer climate, there will be a decrease in dissolved oxygen by up to 15.57% and the water temperature will increase by up to 25.37%. In approximately 85% of the monitoring points analyzed, air temperature explained at least 60% of the variability in water temperature and at least 30% of the variability in dissolved oxygen. Additionally, the projected decrease in precipitation is expected to result in an average decrease in turbidity by up to 50.31% and total solids by up to 22.50%. However, extreme rainfall may continue to occur in the basin, and in this sense, temperature and precipitation events, above the 90th percentile, were associated in more than 90% of cases with a poor or regular water quality index. The stations close to the mouth of the basin showed a higher percentage of extreme temperature events, but a lower percentage of extreme precipitation events. It was also found that precipitation, air temperature, nitrate, total phosphorus, pH, total solids and thermotolerant coliforms jointly explain 33% of the variability in the water quality index. Thus, adaptation and mitigation measures to climate change were proposed to guarantee water quality, helping to effectively manage water resources within the Piracicaba/MG river basin.