تحلیل روند تغییرات پدیدۀ گرد و غبار ناحیۀ غرب ایران طی دورۀ آماری 2018-1979

The trend analysis of dust phenomenon changes in the western region of Iran during 1979-2018





Introduction

Dust, one of the most important known atmospheric phenomena and natural disasters, has attracted the attention of many thinkers and researchers in various branches of science, including atmospheric science. The origin and mechanism of formation, transmission, and diffusion, as well as the consequences of this phenomenon, are studied with various techniques and methods. Countries located in the arid and semi-arid belt of the world, including Iran, have always been involved with the phenomenon of dust. The occurrence of successive droughts in recent years and the possible consequences of climate change in the field of desertification have made dust storms the focus of many researchers' attention (Shahkoi and Rahmani, 2018).

Data and methods

For 18 selected stations in the annual time series (1979-2018), first, the statistics of both Mann-Kendall and Sen,s slope non-parametric tests were calculated. After that, the significance of their results was tested at the 95% confidence level. In this research, to evaluate the frequency of days with dust, weather codes 06 and 07 were prepared in the west of the country, and maps of days with dust were drawn. In this way, the mentioned maps were analyzed on the annual and seasonal scale of codes 06 and 07 using the IDW interpolation method in the ArcGIS 10.7 software environment. In addition to that, the trend of changes in the days with the dust of weather codes 06 and 07 during 40 years was analyzed based on the non-parametric Mann-Kendall and Sen,s slope statistical methods, as well as the charts for determining the 40-year jump points of codes 06 and 07 using the method Mann-Kendall was evaluated. Finally, codes 06 and 07 were interpolated annually and seasonally by the IDW method in the ArcGIS 10.7 software environment.

Results and discussion

Based on the findings of the present research, the frequency of annual occurrence of codes 06 and 07 (1979-2018) in the west of Iran showed that in code 07, the highest amount of dust phenomenon is related to Sanandaj and Kermanshah stations, and in code 06 stations Sanandaj, Kermanshah, and Abadan are the most abundant. The results of the frequency of seasonal occurrence of code 06 showed that dust covers a larger area in the spring season. In the summer season, there is more dust phenomenon in the northeastern parts of the region. And in the autumn season, a noticeable decrease in the frequency of dust occurrence was observed. Finally, the frequency of dust occurrence has decreased in the winter season as well as in the autumn season. The results of the frequency of seasonal occurrence of code 07 also indicate that the dust phenomenon was the most frequent in the spring of Sanandaj and Saqqez stations. And the lowest frequency of occurrence in spring is assigned to Ramhormoz station. In the summer season, more dust phenomenon occurred in the northeastern parts of the region, i.e. Bijar and Qorveh stations. Significant decreasing trend; In both codes 06 and 07, Dezful and Ramhormoz stations show a decreasing trend. a significant trend of increase; It includes the stations of Abadan, Bandar Mahshahr, Dehlran, Sara Roud, Saqqez, and Sanandaj in code 06. And in code 07, Bijar, Ravansar, Sarpol Zahab, Saqez, Sanandaj, Qorve, and Kangavar stations have a significant increasing trend. The jump graphs of dusty days in code 06 of Abadan and Sanandaj stations showed an increasing trend, and in code 07, the mentioned stations continued to show an increasing trend for most of the years.

Conclusion

The significant increasing trend of the phenomenon of dust showed that the highest frequency of occurrence in the stations of Abadan, Bandar Mahshahr, Dehlran, Sara Roud, Saqez, and Sanandaj in code 06 and code 07 Bijar, Ravansar, Sarpol Zahab, Saqez, Sanandaj, It has been Qorve and Kangavar. A significant decrease trend of codes 06 and 07 have occurred in Dezful and Ramhormoz stations. The results of the annual charts for determining the mutation points of code 06 during the last 40 years in Abadan and Sanandaj showed that the increasing trend has increased in recent years. And in code 07, the mentioned stations have continued to increase in most of the years. According to the distribution of stations with significant trends in western Iran, it can be concluded that the trends are subject to a certain order. In code 07, on an annual scale, the highest amount of dust is related to Sanandaj and Kermanshah stations, and in code 06, Sanandaj, Kermanshah, and Abadan stations have the highest frequency. The reason for the occurrence of more dust in the spring season should be considered to be the combined factors and the exit of the western winds from the country. In the summer, the very dry air dominating the deserts of the neighboring countries causes the instabilities of these regions to turn into dust. In autumn and winter, which coincides with the arrival of external systems with instability and humidity in the country, a decrease in the frequency of dust occurrence is evident in some study stations.



Keywords: trend analysis, frequency of dust occurrence, Man-Kendal, Sen’s Slope, west of the country