Synopsis analysis of cold waves in Ardabil city and estimation of return periods and its changes in the coming years

To check the consensus, the average temperature data was obtained from the Meteorological Department of Ardabil Province and the days with temperature below -10°C during the statistical period (1355-1400) were selected as cold days, then the trend of the time series of the frequency of freezing days with the least square error method in the model Linear regression was determined and its results showed a decreasing trend from 2010 onwards. Finally, for the simultaneous analysis of atmospheric factors, 25 January 2016 was selected as a representative through the ward hierarchical clustering method. Next, the data of the upper levels of the atmosphere were received from the website (NCEP/NCAR) and synoptic maps were drawn in Gardes. The results of the analysis of these maps showed that the Siberian thermal high pressure system played an effective role in transferring cold air from northern latitudes to the studied area. In addition to this phenomenon, the location of the study area in front of the European Ridge has resulted in negative air circulation conditions, which resulted in the strengthening of downward currents and a decrease in air temperature. Hyfran-plus statistical model was used to estimate the return periods of cold waves, and the result showed that the stationarity test (Wald-Wolfowitz) and the normal statistical distribution were more accurate in determining the return periods of cold waves. And the results of the Chi-Squared test also showed that it is possible to ensure the extraction of the results at a significant level of 5%. Finally, in order to predict changes in the temperature parameter, using the CanESM2 general circulation model, under three scenarios RCP2.6, RCP4.5, and RCP8.5, the future perspective of the period (2020-2050) was examined. Its results showed that the model had the necessary ability to simulate the average temperature.