Impact of Climate Change and Land Use Land Cover Change on Stream Flow of the Teesta River Basin under CMIP6 Climate Scenarios

Abstract

The Teesta basin, shared by Bangladesh and India, undergoes profound changes due to land use and land cover (LULC) dynamics combined with climate change, significantly impacting its water balance. This study intends to analyse the combined effects of future LULC changes and climate change on the stream flow of the Teesta River. Employing a cellular-automata model, we accurately predicted LULC for 2020 and projected scenarios for 2050 and 2080. A semi-distributed hydrological model, Soil Water Assessment Tool (SWAT) is used to generate flow for the base period (1995-2014), the near future (2035-2064), and the far future (2071-2100). SWAT model is forced by 8 General Circulation Models (GCMs) under two Socioeconomic Pathways (SSP245 and SSP585). Satellite image analysis showed notable LULC changes, with substantial increases in agricultural (0.49%), water bodies (4.24%) and settlement areas (1.67%), while a decrease in forest (1.45%) and sand bar (5.49%) decreased from 2000 to 2010. During 2010 and 2020, increases in agricultural (2.77%), water bodies (7.7%) and settlement areas (8.59%), while decreases in forest (1.36%) and sand bar (0.18%) were found. The CA-Markov prediction indicates significant future increases in settlements and agricultural land by 2050 and 2080, coupled with reductions in forest, water, and snow cover. The calibrated and validated SWAT model effectively simulated discharge, yielding satisfactory results. Projected changes in discharge during the monsoon and winter periods were examined under different scenarios. Monsoon discharge is predicted to increase by 26% to 38% in the near future and 30% to 45% in the far future. Conversely, the winter/dry period may experience a decrease of 46% to 49% in the near future and 38% in the far future for SSP245 and SSP585 scenarios, respectively. Considering LULC changes to account, additional discharge increases during the monsoon are projected, with slight increases in the dry period during the near future and decreases during the far future. This study anticipates an increasing trend in peak flow during the monsoon and a declining trend in mean flow during winter without further upstream water control. Understanding and managing the combined effects of LULC changes and climate change on the hydrological dynamics of the basin is of utmost importance for sustainable water resource management in the region.