Land Degradation Processes of Silabati River Basin, West Bengal, India: A Physical Perspective

Abstract

Degradation of land indicates a definite decline in productive capacity and environmental function of land. Almost half of the total terrestrial land faces land degradation due to different processes. The tropical, temperate and arid environment lead to different processes of land degradation. Water-related soil erosion is deemed to be one of the dominant processes for the degradation of lands in the tropical and subtropical areas of the world. Arid and semiarid regions, on the other hand, face vulnerability owing to wind or vegetal degradation related land degradation processes. Tropical plateaus of the world face a distinct type of land degradation which is generally created by water erosion processes. The present study involves understanding the physical processes of land degradation in tropical plateau environment. Chotanagpur plateau is one of the most degraded region in tropical eastern India; mostly eroded by water. Granite–gneiss geological formation, low-to-medium developed soil cover, undulating lateritic uplands, high drainage density, semi-humid climate (35–40 °C of average monthly temperature; 100–140 cm of annual rainfall) and dry tropical deciduous forest areas make the River Silabati basin a true representative of plateau region of tropical environment. Erosion by water, degradation of vegetation and declining soil quality are the major processes of land degradation in the Silabati basin. Different physical parameters causing the degradation of the land include topographic features, edaphic maturity, hydrological features and vegetation cover span. Remote sensing (multispectral information), elevation data (DEM), meteorological data, field observation and thematic maps are being used to unveil the possible mechanisms of land degradation in tropical plateaus. Granite–gneiss geological formation is the foundation for developing an undulating topography in the basin. Less developed soil profile, low organic matter and poor structure of soil cause high soil erosion. The dissected highland and crests of undulating plateau cause topographic hindrance in productivity of land. High drainage density and frequency in rugged upland cause high soil erosion. Decreasing rainfall and increasing aridity (P/Potential evapotranspiration (PET)) cause threats of water stress condition in the region. Green biomass cover area is also continuously declining. Through overlaying the different physical factors (geological formation, soil characteristics, geomorphological characteristics, etc.) of considerable importance in geographic information system (GIS) environment, the variability in the level of land degradation is mapped. It is found that with intense eroded laterite soil cover, middle reaches of Silabati basin are more susceptible to soil erosion within the whole basin.