Hydrological Impact of Land Use and Climate Change on The West Coast River Basins of Karnataka

Abstract

The Western Ghats of India is an environmental and climate-sensitive region of India. The Western Ghats are the mountainous forest range of a tropical region that play significant role in distributing Indian monsoon rains. Three west-flowing rivers of the Western Ghats representing different levels of anthropogenic influence were chosen for this study to understand the individual and combined effect of land use land cover (LULC) and climate change (CC) on the hydrology of river basins that spread over the northern, middle and southern portion of the west coast Karnataka. The study was carried out with five objectives which include (i) Assessment of satellite and India Meteorological Department (IMD) rainfall products for streamflow simulation in the study area, (ii) To investigate long-term changes in current LULC and model predicted future LULC scenarios on streamflow, (iii) To evaluate the impact of long-term climate change on regional hydrology using SWAT and to assess the river basin responses, (iv) To assess the combined impact of land use land cover change and climate change over the study area, (v) Scenario analysis of the combined effect of land-use change and climate change on blue water and green water availability. Evaluation of satellite precipitation data was performed using the Tropical Rainfall Measuring Mission (TRMM) and Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), employing a semi-distributed hydrological model, i.e., Soil and Water Assessment Tool (SWAT), for simulating streamflow and validating them against the flows generated by the India Meteorological Department (IMD) rainfall dataset. The historical land use (LU) changes were studied for four decades (1988– 2016) using the maximum likelihood algorithm and the long-term LU (2016–2100) was estimated using the Dyna-CLUE prediction model. Five General Circulation Models (GCMs) were utilized to assess the effects of climate change (CC) and the SWAT model was used for hydrological modeling of the three river basins. To characterize granular effects of LU and CC on regional hydrology, a scenario approach was adopted and three scenarios depicting near-future (2006–2040), mid-future (2041–2070), and far future (2071–2100) based on climate were established. iIt was observed that the IMD rainfall-driven streamflow emerged as the best followed by the TRMM, CHIRPS-0.05, and CHIRPS-0.25. The impact of climate change was more predominant than the impact due to land use land cover. However, deforestation and the conversion of other LULC into an unorganized plantation/ agriculture with urban expansion contribute to an increase in streamflow. As per the water availability and vulnerability assessment, the Aghanashini basin was classified under the extremely vulnerable sector, Gurupura and Varahi basins under the low vulnerable sector for water scarcity. The thesis is an attempt to study the LULC comprehensively on the impact on rivers of the Western Ghats of India and is an effective tool in understanding the hydrological impacts and adopting strategies to counter the impacts of LULC and CC.