Tipologia fisiográfica das bacias contribuintes das estações fluviométricas do estado do Ceará obtida por análise de agrupamento

Abstract

The hydrological availability in the semi-arid region of Ceará is strongly controlled by the behaviour of its river basins, which makes an integrated knowledge of their physical characteristics essential. This study aims to physiographically characterize and propose a typology for the contributing basins associated with streamflow gauging stations in Ceará, in order to support hydrological regionalization studies and water resources management. A total of 63 contributing basins were delineated in a GIS environment (QGIS/GRASS) from a hydrologically conditioned Digital Elevation Model, using the gauging stations as outlets. For each basin, parameters describing basin size and shape, drainage network, relief, soils, land use/land cover and lithology were computed. The variables were standardized and subjected to Principal Component Analysis (PCA), which condensed most of the data variance into three principal components. K-means clustering was then applied in the PCA space, and the solutions with K=4, K=5 and K=6 were compared. The configuration with K=5 was selected based on silhouette index values, internal physiographic consistency and spatial coherence of the clusters. From the mean values of the variables in each cluster and their spatial distribution, five types of basins were identified: (i) crystalline dissected basins with high Curve Number; (ii) large elongated crystalline basins; (iii) basins with high soil water storage capacity and lower drainage density; (iv) transitional basins with lower crystalline proportion and more circular shapes; and (v) small steep basins associated with escarpments and plateaus. The resulting typology is consistent with the main geological domains and relief units of the state and provides a useful framework for basin comparison, selection of representative units and regionalization of hydrological information in data-scarce areas.