Quantifying the impacts of anthropogenic changes and climate variability on runoff changes in central plateau of Iran using nine methods

•Nine methods were used to investigate anthropogenic changes and climate variability.•Runoff changes in two selected areas were investigated.•Climate variability played a key role in runoff decline in the Ghaleh-Shahrokh watershed.•Anthropogenic changes had a major role in runoff decline in the Javanmardi watershed.•Each method has its advantages and disadvantages. Quantification of affecting factors on river regime changes can be greatly helpful for water resources planning and management in the basin. Both anthropogenic changes and climate variability have affected rivers’ regime and led to considerable social and economic impacts. Observations in most parts of the world indicate that the hydrological cycle has been influenced by human activity besides of climate variability. In this study, 9 different methods which are divided into three general categories have been used to determine the impact of anthropogenic changes and climate variability on runoff changes in two watersheds in the central plateau of Iran, including Ghaleh-Shahrokh and Javanmardi watersheds. The results indicate that climate variability plays a dominant role in runoff decline in the Ghaleh-Shahrokh watershed, accounting for 60.2% of the total decrease, while human activities accounted for 39.8 %. In the Javanmardi watershed, anthropogenic changes played a dominant role in runoff decline, accounting for 77.1% (on average). In comparison, 22.9% (on average) of the decrease was attributable to climate variability. Sensitivity analysis of the annual mean runoff shows that precipitation plays a key role in runoff changes in both study areas. After precipitation, changes in potential evapotranspiration and temperature have the greatest impact on the annual mean runoff in the studied watersheds, respectively. Comparison of the different applied methods indicate that elasticity-based methods are the fastest and intuitive methods to investigate the impacts of anthropogenic changes and climate variability on runoff changes. Despite this, using different methods should be taken into account.