Geographical Research

The global warming process during last century has not only affected on meteorological elements but also affected on onset and end of each meteorological elements. For studying probability changes in time series of onset and end date of temperature thresholds 0 and 5 centigrade in country level and deciding the kind and its direction، daily temperature data during the past 45 years (1962-2006) for 29 synoptic meteorology stations have been used. For doing this research، first، extract onset and end date of temperature in Gliosis code has been implied. The homogeny of time series was tested by run-test and construct missing value by auto-correlation. For distinguishing random data and trends which had in 95% of trusty level some changes، Mann Kendal method was used. The type and onset time trend was calculated and the changes were also calculated in terms of days with graphic of Mann Kendal and moving average 5 year. The findings of this research shows that there are positive trend at Alpha level 0/05 for onset date of 5 centigrade temperature at 11 stations، negative trend for end date of 5 centigrade temperature at 10 stations . There are also positive trend at Alpha level 0/05 for onset date of 0 centigrade temperature at 10 stations، negative trend for end date of 0 centigrade temperatures at 6 stations. The graphical Mann Kendal test also showed that trends could be as calm; jumping that each of them could be as descending and ascending.