LAUSR

The study aims to investigate the trend of annual variations of dusty day frequency (DDF) in relation to the climatic parameters variations in the eastern part of Iran. In this regard, the data of DDF, temperature, rainfall, and wind speed for 15 meteorological stations during 1951 to 2016 was analyzed. First, the trend of mentioned parameters was detected by using the two nonparametric statistics of Mann-Kendall and Sen’s estimator slope. The results showed that there are significant spatial and temporal differences in DDF in eastern Iran, and in general, it is significantly higher in southeastern and southern areas with an annual average of 160 days than the northern areas. The highest DDF occurs in the months of July and June. The output of Mann-Kendall test showed a significant increasing trend in Zahedan, Iranshahr, Tabas, Garmsar, and Chabahar stations, while most of the stations located in the northern side had decreasing trend. The maximum upward rate of DDF in Iranshahr, Tabas and Zahedan stations was calculated as 1.35, 0.96, and 0.78 days per decade, respectively. The correlation coefficients showed that there is a positive (negative) correlation between DDF and wind speed and temperature (rainfall), and the wind speed fluctuation was the most effective climatic parameter in DDF variations. The study of dust storm wind roses showed that although dust storm occurs under various winds, since most winds blew from northwest to northeast (320 to 040 degrees clockwise), the effective role of 120-day wind of Sistan in dust storm activity was documented.