Mapping land degradation in the Gilbués region, northeastern Brazil, using Landsat TM images

Abstract

Several areas of land degradation are present in the northeastern part of Brazil, resulting primarily from old practices of vegetation clearing and burning for subsistence farming and grazing. However, no reliable information is currently available on the extent of these areas and whether they are expanding over time. Taking the Gilbués region as an example, this study shows the potential for obtaining this information using multitemporal dual-season Landsat Thematic Mapper (TM) imagery. We used digital image processing, which involved the enhancement of soil-fraction images by segmentation/region classification and Normalized Difference Index (NDI) techniques. The results show highly degraded soils covering an almost continuous area of approximately 600 km2. The data also show that, over the past two decades, land degradation has been concentrated mainly along and in the heads of drainage systems, a pattern that indicates removal of riparian forests, thereby compounding the serious problem of sediment loading in the streams in the area. We show that satellite remotely sensed data can provide valuable information in support of environmental policies for northeast Brazil.