Quantification and uncertainty of the impact of climate change on river discharge and sediment yield in the Dehbar river basin in Iran

Purpose The purpose of this study is to identify future changes in weather variables (precipitation and temperature) due to climate change using different general circulation models (GCMs) for different emission scenarios, so as to assess the impact of climate change on river discharge and sediment yield in the Dehbar river basin in Iran. Materials and methods The magnitude and uncertainty of the impact of climate change on river discharge and sediment yield in the Dehbar river basin in Iran is quantified using a calibrated and validated SWAT model with future weather inputs generated using the LARS-WG6 program to downscale the output of five large-scale GCMs for three possible emission scenarios (RCP26, RCP45, and RCP85) and the period 2021-2040. Results and discussion Annual maximum and minimum temperatures are projected to increase by 22-28% and 65-84%, respectively, with a 1-month shift in temperature peak. The future rainfall amounts show both increasing (fall and winter) and decreasing (spring and summer) trends. Future temperature and rainfall patterns are predicted to cause the largest flows to occur a month earlier (February instead of March), an increase in discharge in the wet months of fall and winter (up to 137%) and a decrease in the dry months of spring and summer (down to - 100%). Sediment yield, which is caused by runoff (also controlling river discharge), has a similar projected trend, with a general decrease in spring and summer (down to - 95%) and an increase in fall and winter (up to 340%). The coefficient of variation of the future monthly, seasonal and annual river discharges and sediment yields are relatively low, revealing a general agreement in projections among the different GCM and RCP scenarios considered. Conclusions This study highlights the significant negative impact of climate change on the Dehbar river basin, with amplification of river flows and sediment concentrations in the wet season and increased water scarcity in the dry season. Both effects may adversely impact the region's livelihood (cultivation, fish farming) and land resources.