Evaluating the impacts of anthropogenic, climate, and land-use changes on streamflow

Abstract

Abstract Surface water resources and their contribution to the water balance components are crucial for effective water resource utilization and management in arid and semi-arid regions. Several factors, including natural and human-induced, can affect river discharge. This study aims to examine the influence of land use changes and climate variations on the monthly average rainfall time series in the Talar River basin, situated in the central Alborz watershed in northern Iran. To investigate the impact of human factors, namely land use change and point source operations, on monthly average streamflow, the DBEST (Detecting Breakpoints and Estimating Segments in Trend) method was used to detect any breakpoint in the streamflow time series caused by gradual changes in land use and climate. The Soil and Water Assessment Tool (SWAT) model was used to simulate the basin at two stations, Kiakola and Shirghah, between 2001 and 2020. The model setup for this study used various datasets, including a Digital Elevation Model (DEM), hydrological and meteorological data, stream network, land use maps, soil texture maps, and point source operations parameters. The land use maps were created by integrating data from Landsat 5 and 8 and MODIS satellites for the years 2001 and 2019. Calibration and validation at the Kiakola station showed that the Nash-Sutcliffe model (NSE) had an efficiency of 0.8 and 0.76, respectively, while at the Shirghah station, the same values were 0.84 and 0.75. The SWAT model yielded satisfactory results, enabling the contribution calculation of climate change factors, land use changes, and point source operations on water levels in the basin. Findings revealed that human activities, specifically the combined impact of land use change and point source operations, had a 60% influence on the monthly average streamflow of the Talar River. Further analysis comparing the relative contributions of the three influential factors showed that the combination of land use changing and water harvesting played the most significant role in altering the basin's outflow on a monthly scale.