Spatial Analysis of the Temporal Long-Term Variations in Frequency of Dust Storm Days in Iran

In this study, the total seasonal and annual frequency of dust storm days (DSD) of 44 synoptic stations with long-term statistics over a 50-year period from 1968 to 2017 was analyzed using the Mann–Kendall nonparametric test, kriging, and radial basis function (RBF), spatial interpolation methods, directional distribution of spatial statistics, and mean center. Based on the results of Mann–Kendall test and related maps using RBF, it was found that about 30 stations had an increasing trend, most of which demonstrated a significant upward trend in the southern regions and western part of Iran. Significant decreasing trends were observed in the northern part. The results of DSD zoning showed that the maximum incidence of DSD occurs in spring and summer, and more in the southern and western parts of Iran, while they are much less frequent in the middle and northern regions of Iran. Investigation of the directional distribution of spatial statistics and the decadal foci for five decades, i.e., 1968–1977, 1978–1987, 1988–1997, 1998–2007, and 2007–2017, showed that the foci of DSD in the first and second decades moved to the east, but subsequently shifted to the west in the fourth and fifth decades. Given that the movement has been to the west, it can be said that the frequency of DSD is increasing from southeast to west. The results of directional distribution also showed that in all seasonal and annual time scales, the focus of DSD in Iran is from southeast to west.