Impacto da urbanização na microbacia do rio Cascavel – município de Cascavel – Paraná – Período 2015 a 2020

Abstract

Rapid and unplanned urban growth has caused significant changes in watershed dynamics, compromising their capacity for hydrological regulation and their environmental sustainability. The Cascavel River micro-watershed, located in the municipality of Cascavel, Paraná, Brazil, with a catchment area of 50.51 km², is a representative example of this process, as its headwaters lie within the urban perimeter and are directly affected by urban and agricultural expansion in the region. This study analyzed the impacts of urbanization on the streamflow of the Cascavel River micro watershed, investigating the relationship between increasing soil sealing, land use and occupation, and the watershed's hydrological response over time. The methodology combines analysis of historical streamflow and precipitation records from 2002 to 2020, supervised classification of Sentinel-2 satellite imagery (2015-2020) processed in QGIS using the Maximum Likelihood algorithm (MAXVER), with an Overall Accuracy of 86.57% and a Kappa coefficient of 0.8159, and multivariate statistical analysis through Principal Component Analysis (PCA) and Hierarchical Cluster Analysis. A continuous expansion of the urbanized area was identified, from 28.41% to 31.28% of the micro-watershed (+1.45 km² over six years), at the expense of temporary cropland and remaining forest cover. Mean daily streamflow dropped from 1.53 m³/s in 2018 to 0.33 m³/s in 2020 — a decrease of approximately 78% — including an interval between 2018 and 2019 in which precipitation varied by only 3.4% while streamflow fell by 66%. The multivariate analysis organized the data into two orthogonal factors — a rainfall factor and a hydrological response factor — accounting for 79.70% of the total variance, evidencing a partial decoupling between precipitation and streamflow. The results indicate a contribution of urbanization and soil sealing to the variations in the Cascavel River's streamflow, with effects on surface runoff, infiltration, and basin recharge, and risks associated with a higher frequency of extreme events, such as floods and severe droughts. The findings provide technical support for public policies and for environmental recovery and urban planning strategies, with a focus on water resources conservation and the mitigation of the effects of urban densification.