Document Type : Research Paper

Authors

• Jalil Helali ¹
• Ebrahim Asadi Oskouei ²
• Touran Hosseinzaheh ³
• Mansoureh Kouhi ⁴
• Seyedeh Maryam Mohammadi ⁵

¹ Department of Irrigation and Reclamation Engineering Department, Faculty of College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

² Climatological Research Institute,, Atmospheric Science and Meteorology Research Center (ASMERC), Tehran, Iran

³ Department of Natural Geography, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

⁴ Climatological Research Institute, Mashhad, Iran

⁵ Department of Environment, College of Basic Science, Islamic Azad University, Hamedan Branch, Hamedan, Iran

Abstract

Keywords

• Dust storm (DS)
• spatiotemporal trend
• Arid climates
• Mann-Kendall trend

20.1001.1.2008479.1402.54.3.6.0

Main Subjects

• ...

EXTENDED ABSTRACT

Introduction

Dust storm (DS) is an atmospheric phenomenon that causes economic damage to the environmental and agricultural sections. The occurrence of this type of weather has exerted an extremely adverse effect upon the environment. In recent years, the frequency and intensity of dust storms have increased dramatically in Iran (Gerivani et al., 2011; Miri et al., 2021). These atmospheric phenomena have been recognized as having a very wide range of environmental, health and climate impacts in the southern provinces of Iran including the southwest of Khuzestan Province and the northern part of the southeastern Sistan and Baluchistan Provinces (Misconi & Navi, 2010). This study aims to investigate and compare the annual and seasonal variability of DS days before and after the 2005 year using 42 synoptic stations of DS days during three periods: 1977-2005, 2005-2021 and 1977-2021.

Material and Methods

Study Area

Iran, with an area of 1,648,195 km2, between the eastern longitudes of 44–63° and the northern latitudes of  25–45°, is located in the dust belt that extends from the west coast of North Africa, over the Middle East, Central and South Asia, to China. This country borders the Caspian Sea in the north and the Persian Gulf and Oman sea in the south. The Zagros in the west and the Alborz in the north are the two ranges of high mountains of this country which have a vital role in preventing the Mediterranean and the Caspian Sea winds near the central plateau of Iran, respectively. The country has a different type of climate. It is mild and quite wet on the coast of the Caspian Sea, continental and arid on the plateau, cold in the high mountains, and hot on the southern coast and in the southeastern region (Abbasi et al., 2021).

Meteorological data

Weather stations worldwide are used to record surface meteorological observations as defined by the WMO. In these regards, the codes of dust events are assigned to reflect the severity and proximity of each event. For this article, dust codes (05, 06, 07 & 08), recorded at 42 stations over Iran, were the main data source. In order to investigate the main seasons of dust storm occurrences, seasonal sub series were used, i.e. spring (from April to June), summer (from July to September), autumn (from October to December) and winter (January to March) of period 1977-2021. This period was divided into two sub-periods before and after 2005. The number of DS days of these two sub-periods and total period (1977-2021) were finally compared.

 Methods

The purpose of the Mann-Kendall (MK) test (Mann 1945, Kendall 1975, Gilbert 1987) is to statistically assess if there is a monotonic downward or upward trend of the variable of interest over time. To calculate the trend, list the data in the order in which they were collected over time, , , …, , which denote the measurements obtained at times 1, 2, …, n, respectively. The MK test statistics are calculated based on the sign of the difference between two consecutive observations, 𝑠𝑔𝑛 (𝑥𝑗 − 𝑥𝑖).

The sign function is

(𝑥) = 1 𝑖𝑓 𝑥 > 0; = 0 𝑖𝑓 𝑥 = 0; = −1 𝑖𝑓 𝑥 < 0                                                                                    (1)

and then

𝑀 = ∑ (𝑥𝑗 − 𝑥𝑖)                  1≤𝑖≤𝑗≤𝑛                                                                                                 (2)

Under the null hypothesis (𝐻₀) of no monotonic trend, M has asymptotically normal

distribution with mean zero and approximated variance:

(𝑀) = 𝑛(𝑛 − 1)(2𝑛 − 5)/18                                                                                                                (3)

Results

The obtained results show that a sharp increasing trend in the frequency of dusty days in the period after 2005 is conspicuous compared to the period before 2005 and long-term, especially in the extra-arid climates. The variations revealed a significant positive trends in extra-arid, arid and semi-arid climates respectively, up to 93, 83, and 88 percent of stations (PS) in winter, 71, 50 and 44 PS in spring, 57, 58 and 13 PS in summer and 64, 83 and 63 PS in autumn. In annual scale, a significant positive trend of DS was found to be 64, 83 and 63 PS for extra-arid, arid and semi-arid climates, respectively. Moreover, a clear seasonal pattern of dust emissions shows increases in the frequency of dust events in spring and winter which indicates the extension of this phenomenon to the wet seasons.