Modelling land-use and climate change impacts on hydrology: the Upper Ganges river basin

Abstract

This thesis explores the effects that large-scale land-use/cover change (LUCC) and climate change pose to the terrestrial water cycle, by developing a case study in the Upper Ganges (UG) river basin, in India. In an area experiencing rapid rates of LUCC and changes in irrigation practices, historic land-use maps are developed, based on satellite images, to investigate historical trends of LUCC. Future projection scenarios of LUCC for years up to 2035 are derived from Markov chain analysis. To explore the impacts of those changes in hydrology, the generated maps are used to force the Land Surface Model (LSM) JULES. JULES is found to be reasonably skilful in terms of its ability to reproduce observed streamflow. However, the results indicate that there is much room left for improved estimates of evapotranspiration (ET) fluxes, which JULES is found to over-predict. By dynamically coupling JULES with the crop model InfoCrop, the simulated ET fluxes are improved, compared to the original JULES model. The difference in mean annual ET between the two models (coupled and original) is approximately 150 mm/yr and indicates the potential error in ET flux estimations of an LSM without dynamic vegetation. The impact of LUCC and climate change on the hydrological response of the UG basin is quantified, by calculating variations in hydrological components (streamflow, ET and soil moisture) during the period 2000–2035. Severe increases in the high extremes of flows (+40% in the multi-model mean) are being projected for the nearby future (2030–2035). The changes in all examined hydrological components are greater in the combined land-use and climate change scenario, whilst climate change is the main driver of those changes. These results provide the necessary evidence-base to support regional land-use planning, advanced irrigation practices and develop future-proof water resource management strategies under a water-limited environment.