Investigating trend of frequency changes of sultry days in southern half of Iran

Investigating the climatological and meteorological phenomena change trends has a particular importance in climate change studies. In this study, hourly data of vapor pressure related to 15 synoptic station in the south of Iran within a statistical period of 30 years (1980-2009) are collected from Meteorological Organization of Iran to detect and achieve the trend frequency of changes within sultry days in the southern of Iran. After collecting data, a database was established based on maximum vapor pressure equal to or more than 18.8 hPa. The frequency of sultry days are extracted for all target stations with regard to two time scales of annually and seasonally. The Sen’s Slope Estimator Non-Parametric Method was used to detect trend of frequency changes of sultry days. The results showed no significant trend in frequency of sultry days in target stations with the probability level of %95 in three seasons of autumn, winter and spring. The only station which showed a significant trend was Dezfoul station (trend slope: -1.05) while a reducing trend was observed in summer. Four stations of Kerman (trend slope: -0.1), Dezfoul (trend slope: -1.46), Iranshahr (trend slope: -1.08) and Zahedan (trend slope: -0.16) showed a significant trend in the frequency of sultry days while a reducing trend for all four stations was observed in annual scale.