Impact of land use and climate change on monsoon flow of Ganges river basin using swat model

Abstract

Ganges River Basin is a part of Ganges-Brahmaputra-Meghna (GBM) basin which is second largest river basin system in the world based on drainage. This basin system with an area of 10,87,500 km2 carries enormous volume of 525 km3/yr water through Bangladesh. Water related issues of the basin are due to both high and low flows which will be more effected due to climate change and also due to land use changes. Now a days, global warming causes the change in frequency of rainfall and temperatures. It is alarming that many studies identified significant changes in the climate of this larger South Asian region due to global warming. These changes are very likely to affect the hydrological regimes of the whole Ganges River Basins including the sub-basins and subsequently the flows that enter into Bangladesh from the system. The present study focuses on developing a hydrological model of Ganges River Basin using Soil Water Assessment Tools (SWAT) model to estimate present and future discharge considering the climate change and land use changes. A semi-distributed hydrological model of the Ganges River Basin has been developed using SWAT. A 90-m resolution DEM derived from the Shuttle Rader Topography Mission (SRTM) has been used to delineate catchment boundary. A 300- m resolution of land use data of 2009 has been used. The soil map of the catchment has been extracted from the FAO digital soil map of the world. The gridded rainfall and temperature data have been obtained from Nasa-POWER. The evaluation process of model comprises of sensitivity analysis, calibration and validation. This hydrological model has been calibrated from 2000 to 2007 and validated for 2008 to 2016 at Hardinge Bridge transit (SW 90). The NSE, PBIAS, RSR, R2 values showed satisfactory result for calibration and validation period respectively. The calibrated hydrological model of Ganges River Basin has been used to assess the impact of climate change on discharge of Ganges River Basin by applying different climate change scenarios of selected GCMs. Four climate change scenarios, such as warmest, coolest, driest and wettest were selected based on the projected precipitation and temperature of the 21st century obtained from four RCPs (RCP 2.6, RCP 4.5 and RCP 8.5) of three GCMs (BCC-CSM 1.1, IPSL-CM5A-LR and HadGEM-2 ES). Ganges River Basin projected an increase in the mean annual streamflow for 21st century under the climate projections for almost all the four scenarios considered in this study. It is found that the average annual flow generated from the Ganges River Basin is 330,175.21 Mm3. The results also indicate that the discharge will be changed during dry period and also during monsoon. The average annual flow volume has an increasing rate for 2020s, 2050s and 2080s. An increase in urbanization and deforestation area for all over Ganges River Basin, have been done to analyze the changes of discharge. It has been found that the increasing trend of discharge for land use change scenarios towards the 21st century.