Identificação de limiares de precipitação causadores de inundação em bacias de pequena escala: estudo de caso para o Ribeirão José Pereira, Itajubá/MG

Abstract

Extreme events, such as flash flood, have increased globally, causing significant damage. In Brazil, this concern is worsened by climate change, with phenomena such as La Niña in 2022 and El Niño until 2024. José Pereira river, in Itajubá/MG, crosses the urban area and is susceptible to flooding. This study aims to establish precipitation thresholds that trigger floods in the José Pereira river basin. To this end, the basin was characterized, considering climate data, flood history, topography, soil, land use and subdivision into sub-basins. Subsequently, parameters such as curve coefficient (CN), concentration time and lag time were calculated. It was then possible to select two flood events in the rainy season of 2022 and 2023 to calibrate the HEC-HMS model, using level and precipitation data from stations available in the basin. Furthermore, parameter calibration sought an acceptable fit between observed and simulated data. Based on this, events were chosen for simulation based on a minimum daily accumulation, selected from the historical series records from 2013 to 2023 from the UNIFEI-CEPREMG rainfall station. To define this minimum value, maximum rainfall analysis and return time calculations were carried out, indicating a value of 40 mm in 24 hours. These events demonstrated concentrated and distributed rainfall, highlighting the influence of upstream basins on the variation in river levels during flood events. Detailed analysis revealed that significant precipitation occurs between the first 25% and 50% of the total duration of rainfall triggering overflow or flooding. From the simulations, the minimum accumulated rainfall necessary to exceed 1.5m in river was identified. Through simulations, the minimum volume of accumulated rain necessary to exceed the 1.5m mark in river was determined. Analysis of the resulting graph, together with the logarithmic curve derived from the minimum accumulation in each selected event, revealed that upon reaching 34.60mm of accumulated precipitation, regardless of the duration and distribution of the rain, it becomes essential to issue an alert.