Investigating climatic variables and human activities in the changes of runoff in Qezelozen watershed

In recent decades, the amount of runoff has decreased significantly in a few regions of the world. Human activities and climate change are the two main factors in runoff changing. Accordingly, it is very important to analyze the influencing factors and quantify their impact on the runoff. In this research, the analysis of the process of gradual and sudden changes in the QezalOzen River runoff at the Yesaul hydrometric station in Kurdistan province was carried out using the linear regression method and Pettit's test. The results showed that the runoff time series in the upstream watershed of Yesaul hydrometric station has a decreasing trend and the breaking point of the runoff time series is 1998. According to this, the runoff time series was divided into the base period and the evaluation period. Runoff simulation was done using SWAT model. After entering input data of the watershed in the SWAT model, the model was implemented between 1987 and 2010. From 1987 to 1993 is before the change point. Based on this, syear 1987 was used as warmup, 1988 to 1991 was used for calibration, and years 1992 and 1993 were used to validate the model. SUFI-2 algorithm was used in SWATCUP software package to calibrate the model. Since the number of the parameters in SWAT model is large, before calibration, the sensitivity analysis was done and the sensitive parameters were determined. Examining the results of calibration and validation of the model in the base period showed that the SWAT model has a good performance in simulating the runoff in Yesaul hydrometric station. Also, the results of the study showed that the impacts of climate change (76%) in reduction of runoff during the evaluation period is much higher than the impact of human activities (24%). In general, the current research states the necessity of taking necessary measures to adapt to climate change and create guidelines for human activities for sustainable access to water resources.