Banca de QUALIFICAÇÃO: CARLOS CÉSAR DE ARAÚJO

Analysis of Sediment Yield in the Seridó River Basin, Brazilian Semiarid Region, Using the SWAT Model

Land use and land cover; Hydrosedimentological modeling; SWAT; Seridó River Basin.

The Seridó River Basin (SRB), located between the states of Rio Grande do Norte and Paraíba in northeastern Brazil, is one of the main sub-basins of the Piancó–Piranhas–Açu River Basin and is situated within the Brazilian semi-arid region. The basin exhibits typical characteristics of this environment, including high temperatures, marked spatial and temporal rainfall irregularity, prolonged drought periods, intermittent rivers, Caatinga vegetation, and predominantly shallow soils. It also encompasses the Seridó Desertification Nucleus and the UNESCO Seridó Global Geopark. Over recent decades, the basin has undergone significant land use and land cover changes associated with intensified human activities, making it essential to understand their effects on hydrosedimentological dynamics. In this context, this study aims to analyze the spatial distribution of sediment yield in the Seridó River Basin using the Soil and Water Assessment Tool (SWAT) model, seeking to understand its relationship with precipitation, surface runoff, land use, soil type, and slope. To achieve this objective, quantitative and qualitative methods were employed, based on a literature review, statistical analyses, geoprocessing techniques, and hydrosedimentological modeling. The SWAT model, integrated with a Geographic Information System (GIS), was supplied with topographic, land use and land cover, soil, and climatic data, enabling watershed delineation, the definition of Hydrological Response Units (HRUs), and the spatial analysis of hydrosedimentological processes. Preliminary results showed that the basin is predominantly covered by Savanna Formation, accounting for 59.83% of the total area, followed by Pasture (22.56%) and Mixed Land Uses (13.01%). Validation of the land use and land cover map through field surveys and the Kappa coefficient resulted in a value of 0.668117, classified as indicating very good agreement. The adaptation of the original MapBiomas product enabled the reclassification of vegetation classes into terminology more consistent with the Caatinga ecosystem. The SWAT+ model delineated 21 sub-basins, with areas ranging from 7.10 km² to 1,371.87 km², and indicated a predominance of gently undulating terrain, corresponding to 39.6% of the total basin area. Spatial analysis of hydrosedimentological processes revealed annual precipitation ranging from 564 to 875 mm, with an average of 638 mm, and the highest values occurring in the southern and southeastern portions of the basin. These areas were associated with higher surface runoff, ranging from 160 to 607 mm (average of 349 mm), and sediment yield ranging from 232 to 26,608 t (average of 8,875 t). Sub-basins 18 and 21 were particularly noteworthy, demonstrating the combined influence of precipitation, topography, land use and land cover, and soil characteristics on the basin's erosive dynamics. These findings highlight the importance of integrating geoprocessing techniques, field validation, and hydrosedimentological modeling to improve the understanding of the environmental dynamics of the Seridó River Basin, providing valuable support for the planning and sustainable management of water resources in semi-arid environments.