Tendências em eventos extremos de precipitação na Região Metropolitana de Belo Horizonte: detecção, impactos e adaptabilidade

Abstract

Extreme climatic events have emerged as one of the main manifestations of climate changes, being that the adaptation and minimization of inherent impacts demand studies of the magnitude and frequency of their occurrence. In this context, the present research seeks to identify trends for extreme precipitation events in the Metropolitan Region of Belo Horizonte, in function of the growing concern about its occurrence in the region and also to plan measures to minimize the risks arising from the observed trends. The first stage of the work consisted in the research for flood events in the region, also analyzing daily precipitation data corresponding to the days of floods occurrence, in order to establish an indicative threshold of extreme rainfall. In this sense, trends in precipitation indexes recommended by the Expert Team for Climate Change Detection Monitoring and Indices (ETCCDMI) were studied, including the time series of the annual number of rainy days above the established threshold, for 14 rainy seasons. In the later stages, the trends in maximum annual precipitation with durations less than 24 hours were investigated, and considering the observed changes it was proposed a new IDF curve, as well as measures of urban resilience, by the use of compensatory techniques. The research carried out allowed to obtain 104 flooding cases for the city of Belo Horizonte, with a threshold of 40 mm being determined, which is an indicative of an event with the potential to cause impacts associated with urban drainage. A regional pattern was not detected in the daily precipitation indexes analyzed, however when statistical significance was detected, the indexes showed a predominant positive trend. The station located in the city of Belo Horizonte pointed the increase in precipitation events associated with most of the indices analyzed, being an indication of local change. With regard to sub-daily rains, increases were detected from 2000 onwards only for durations less than 1 hour. In this context, an adaptation of the concept "Minimax Design Life Level: the T1 -T2 p% bounded yearly risk level" was proposed to quantify the rain intensities and to adjust a non-stationary IDF equation, being estimated for the year of 2040 rain intensities up until 48% higher than current estimates. Considering this fact, it was evaluated the impact of the implantation of green roofs and permeable pavements in a watershed of Belo Horizonte, from a perspective of urban renewal, being possible to observe that the increase of the peak flow obtained when comparing the scenarios that contemplate the different prospects of IDF (current and non-stationary), although quite expressive, can be attenuated with the implantation of techniques that will contribute to the reduction of the flow. The results of this study show the hydrological benefits that the implantation of compensatory techniques can promote in face of a scenario of changes in precipitation patterns.