Estimating spatial variation of river discharge in face of desertification induced uncertainty

Abstract

Climate change and global warming along with wide scale forest degradation have induced desertification in different parts of the world including India. The problem of desertification includes excess runoff, soil erosion, etc., which ultimately leads to catchment degradation. A study was performed to analyze the impact of desertification on river discharge. River Ajay, a small tributary of river Bhagirathi in the west of West Bengal was chosen as the study area due to the semideserted condition of the catchment. DIStributed COupled RATional Model (DISCORAT) where Orange County rational method (Rational OC) and MODified RATional (MODRAT) were coupled to estimate river runoff due to desertification-induced uncertainty. The desertification-induced uncertainty was generated by three scenarios where two scenarios represent extreme desertification (Actual-50%) and semi-desertification (Actual-5%). The input variables were modified according to the generated scenarios and applied to DISCORAT model for estimation of stream flow. As the catchment was divided into 16 15/15 grids and contribution of each grid was included in the estimation, the predicted stream flow for the desertification scenarios would give a distributed variation of stream flow and impact of desertification for each grid could be observed from the estimated stream flow at the grids. Cumulatively, a continuous variation of stream flow due to desertification could be generated and analysis could be made about the impact of desertification on stream flow. According to the results, reduction of stream flow was observed due to desertification and the relationship between desertification and reduction of stream flow was found to be inversely proportional, that is, more intense desertification would imply more reduction of stream flow except in the outlet of the river basin where an opposite relationship was observed between desertification and stream flow. A reason for this estimation could be contributed to the reduction of rainfall as considered in the scenarios of desertification. The reversal of relationship at the outlet could be because of runoff-rainfall ration, which was considered to be well above 150% in Actual-50% scenario of desertification. © 2010 Springer Science+Business Media B.V.