Water yield variation as linked to catchment parameters: A biophysical analysis for Kerala, India

River basins are basic hydrological units and considered as the best unit to work out water yields. Biophysical characteristics of a river basin play significant role in determining the water yield of a river basin. This study intends to investigate linkage between water yield and selected catchment parameters. The catchment yield of all major west flowing rivers of Kerala has been considered for this analysis. Drainage basins with smaller areas have been grouped with neighbouring basins to work out catchment efficiency. Methodology followed here consists of i) working out catchment yield index for each basin and ii) computation of biophysical parameters. Out of 28 basins as many as 12 river basins have catchment yield index of less than 1 indicating the characteristics of deficit river basins. It is found that besides, rainfall, the primary determinant of water yield, area under highland, forest coverage and catchment shape contributed to variations in water yield. Soil thickness and infiltration rate are other contributing parameters. It is suggested that this method can be used for inter basin comparison.