Simulation of the effect of global warming on the mean and extreme events of some hydrochemical variables in Shandiz catchment basin Case study: The Case of the general circulation model CanESM2

Changes in the mean and the extreme values of hydroclimatic variables are two prominent features of the future climate. Therefore, simulating the climatic behavior of Shandiz catchment area, an important tourist area in the northeast of the country, will play an important role in identifying the climate condition and potential vulnerability of these areas in the coming decades of climate change. In this study, we will evaluate the effects of climate change on extreme values of the basin micro scaling precipitation and temperature in CanESM2 model using SDSM model and simulating runoff with SWAT model in future decades. To achieve this goal, the daily temperature and precipitation statistics of the 30 statistical years (1961-1990) of Mashhad synoptic station have been used. The data of the CanESM2 general circulation model under RCP2.6, RCP4.5 and RCP8.5 scenarios are also used to predict precipitation, the minimum and maximum temperature for 2041 to 2100. According to the results, the annual precipitation rises 37 to 54 percent from 2041 to2070 compared to the observation period, and the increase in rainfall of the 2071-2100 rises 52 to 66 percent. Precipitation extreme values, the mean of maximum and minimum temperatures in future periods in all seasons of Mashhad station will increase compared to the observation period (1961-1990).In future decades, the average maximum temperature in Mashhad will increase from 4.6 to 0.65 degrees Celsius and the average minimum temperature will increase 53/1 to 22/4. By introducing micro scaled time series of the maximum temperature, temperature, and micro scaled precipitation by SDSM model to SWAT model, the monthly time series of Shandiz watershed runoff at Sarasiab Station was simulated for the two periods of 2041-2070 and 2071-2100 under three distribution scenarios of RCP2.6, RCP4.5 and RCP8.5. For this purpose, first, the model was calibrated and validated using Shandiz hydrometric station runoff for 2003-2012, and the values of R2 were 65 and 52, respectively. Subsequently, with the introduction of micro scaled time series of maximum and minimum temperatures, and micro scaled precipitation by SDSM model to SWAT model, the average annual trend shows that runoff increases in the coming decades. The lowest average annual increase for runoff is in 2041-2070 and RCP4.5 scenario, with an increase of 56.1% over the observation period. The highest increase of average annual monthly runoff is from 2071 to2100 under RCP 2.6 scenario with 53% to 104% runoff compared to the observation period.