Contribuições à dinâmica geomorfológica recente na bacia do rio Javaés, Brasil Central

Abstract

The morphodynamics of rivers are controlled by various external factors, whether natural or anthropogenic. In intertropical regions, Morphodynamic processes have been influenced by the expansion of land use conversion, transforming original vegetation cover into pastures and cultivation areas, as well as by the intensification of climate variability. These factors have triggered changes in fluvial discharge regimes, flooding, erosion, and sediment deposition. These alterations have been observed on the slopes of Brazilian savannas, while studies exploring their relationship with fluvial dynamics remain underexplored. The connection between slope and floodplain processes is particularly important for the Araguaia River Basin, which houses the world's largest fluvial island, Bananal Island. The objective of this thesis was to evaluate how hydrogeomorphological processes are influenced by climate change and land use, especially due to the intensification of agricultural activities in the eastern portion of the island, drained by the Javaés River. The methodology combined Remote Sensing approaches, machine learning techniques, statistical analysis, and field verification. LANDSAT images (1984-2022) were processed on the Google Earth Engine (GEE) platform to map flooded surfaces, water bodies, and sandbars. Supervised classification was applied to distinguish water areas, sandbars, and vegetation. Precipitation, land cover, and land use data were also analyzed using GEE. The Revised Universal Soil Loss Equation (RUSLE) was used to map sheet erosion rates in the sub-basins on the eastern edge of the island. Mann-Kendall (MK) and Sen’s Slope statistical tests were applied to identify temporal trends. The results indicate that climatic seasonality generates unimodal flooding cycles, with higher incidence in flat and basin-like areas. Paleoforms within Bananal Island control connectivity between flooded areas, affecting water flow and sediment deposition. The MK test indicates a reduction in flood occurrence between 1984 and 2022, particularly during the dry months and the beginning of the rainy season. A 57% (6.5 km²) increase in sandbar areas and a 39% (15.2 km²) reduction in water bodies were observed. Changes in the distribution of regional precipitation rates, combined with the expansion of agricultural activities, are contributing to increased sediment input, resulting in imbalances in the dynamics between erosion and deposition in the Javaés River, a tributary of the Araguaia River. The application of RUSLE revealed increased erosion rates, particularly in sub-basins where native vegetation has been replaced by degraded pastures. The highest soil loss rates were observed in the time series, reflecting the impact of intensified agricultural use. Protected areas, such as Bananal Island, demonstrated greater resilience and lower erosion rates compared to surrounding unprotected areas. These results underscore the importance of integrating management strategies to mitigate erosive impacts and preserve the geomorphological integrity of the region, particularly in contexts of increasing anthropogenic pressure and climate variability.