Quantification of the impact of land cover and climate change on water and sediment yield in sub-tropical Himalayas in upstream Teesta river basin, Sikkim

Abstract

The assessment of isolated and combined impact of land cover (LULC) and climate change on water and sediment yield of hilly watershed is essential for sustainable land and water management and social developments. An improved hydrological modelling approach coupled with statistical tools was used to explore the role played by LULC and climate change on key water balance components and sediment yield (SY). The calibrated Soil and Water Assessment Tool (SWAT) model was used to simulate the key hydrological components and SY from 1990 to 2019 (historical) and 2020 to 2059 (near-future). The trends and slope analysis were carried out to understand the temporal shift in meteorological timeseries and to aid in interpretation of climate change impacts on variables.Historically, the LULC change led to decrease in actual evapotranspiration, streamflow, baseflow, and water yield (WY) (∼4 %) and increase in lateral flow, and SY (∼36 %). Consistent results were also obtained in all seasons. In near future, the impact of LULC change on these variables is anticipated to be negligible in all aspects. The climate change under historical scenario has substantially increased the magnitude of all variables at annual scale as well as in all seasons except winter season. The historical increase in annual WY and SY is ∼12 % and ∼25 %. Also, a substantial increase in magnitude of all variables is projected during monsoon under SSP2-4.8 and SSP5-8.5 emission scenario. The suggested approach has promising results in isolating the effect of LULC and climate change on SY, WY and some key hydrological components over upstream Teesta River basin supporting with consistent results from the previous studies from different areas.The SWAT model effectively captured streamflow and SY dynamics at daily timescales during calibration and validation. Additionally, our proposed approach demonstrated promising results in discerning the distinct impacts of LULC and climate variations on WY and SY.