Review the Trend of Frosty Days in Iran

In this study, by the help of interpolated data of minimum temperature of Iran within the time period of 21, March 1961 up to 19 March 2003, the trend of frosty days in Iran was reviewed and studied. An array with dimension 15705*7187 was obtained and day was inserted on rows and cells on the column. For all the months of the year, the number of frosty days on each cell was counted. Nonparametric Mann–Kendall test was used for identification of the trend and Linear regression test of least square method was used for calculation of the trend slope. In total, the study results showed that, the number of frosty days in an extensive area of Iran has a negative and decreasing trend. These regions located on northwest and also on even and plain areas at the central, eastern and southern part of Iran. Only on a small part of higher elevations including Zagros and Alborz mountain chains, the trend is positive The most extensive negative trend was observed in January while the most extensive positive trend observed in March. The frosty days in Iran summer and May is fixed and without any trend.