Analysis of the trend of snowmelt changes in Iran and its impact ability from changes in the Mediterranean wave of westerly winds

Snow is considered as one of the climatic elements of water supply for life. Therefore, this study was conducted aimed to investigate the trend of changes in snowmelt in Iran and its impact on changes in the Mediterranean wave of westerly winds. For this purpose, we provided snowmelt and geo-potential height data of 500, 600, and 700 hPa atmospheric levels from the European Center for Medium-Range Weather Forecasts (ECMWF) version ERA5 with a spatial resolution of 0.25 * 0.25 ° for 1979-2019 January, February, March, April, November, and December. First, the trend and slope of monthly snowmelt changes in Iran were evaluated using non-parametric Mann-Kendall statistical tests and Sen.’s slope estimator. Then, using the percentile method, 25% and 75% percentiles of monthly snowmelt values in Iran were determined. The relationship between the changes in the Mediterranean wave of the westerly winds and the months with snowmelt values lower and higher than 25% and 75% percentiles was measured. Finally, the Middle East Synoptic Index (MESI) and decade expansion were used to analyze the impact of the monthly decreasing trends of snowmelt of the Mediterranean wave changes of the western winds in Iran. The results showed that in January, February, March, April, and December, the mean monthly snowmelt in Iran has a decreasing trend. In addition, a relationship was between the Mediterranean wave heights of the westerly winds in January, February, March, November, and December with the mean snowmelt of lower and higher than 25% and 75% percentiles, respectively. Also, the results showed changes in the height of the Mediterranean wave of westerly winds. It seems that these changes are among the factors affecting the decreasing trend of snowmelt in Iran, which is especially evident in the third and fourth decades (since 1999 onwards) in January, February, March, November, and December.