Extended Abstract

Introduction

One of the problems that has been spreading in the last few years as a result of climate change, human intervention and irrational use of natural resources and its destruction is the phenomenon of dust. The characteristics of Iran's drought show that a large part of Iran is not safe from this phenomenon and experiences the effects of this destructive phenomenon in proportion to its natural reality. Especially the southern, eastern and central parts of the country are more vulnerable due to large fluctuations in rainfall amounts. Khuzestan province is frequently exposed to severe dust storms due to its semi-arid climate and its proximity to the vast expanse of neighboring deserts such as Iraq, Arabia, Syria and North Africa, and the living conditions in this province become critical. Due to the increase of drought in recent years in the region and neighboring deserts, the frequency of days with dust has increased greatly, especially in the hot season of the year; therefore, the purpose of the current research is to analyze the trend of dusty days and investigate the effects of the dusty phenomenon in the studied area. Accordingly, considering the damages and problems caused by the dust phenomenon in Khuzestan province and the need to know it accurately in terms of examining the trend of dust days and analyzing it, it is necessary to plan to reduce the damages and deal with this environmental crisis.



Materials and methods

Khuzestan province, with an area of about 64.05 square kilometers, is located in the southwest of Iran, between 47° and 38´ to 50° and 33´ east longitude and 29° and 57´ to 33° north latitude from the equator. This province occupies about 4% of the total area of the country, which is considered the tenth province of the country.

In this research, the data of 19 stations of Khuzestan province have been used to analyze the trend of dusty days in southwest Iran. The desired data from the year of establishment of each station to 2015 were obtained in raw form from the Meteorological Organization. First, the data were sorted in Excel software, then the data were processed in Minitab software to check the trend of dust days. The data includes dust codes (98, 35-30, 09, 08, 07, 06). Dust codes were arranged in 19 stations by month in 8 hours of observation. Codes 06 in total dh (extra-local dust phenomenon), codes 09, 08, 07 in total lde (local dust phenomenon), codes 30-32 and 98 in total Mds (light to moderate dust storm) and codes 33-35 in total sds (sand storm phenomenon) ) it placed. By sorting and arranging each dust code in the DH, LDE, MDS, SDS folders, mentioning the horizontal visibility in each dust code, then all the mentioned codes were included in the total of dusty days. Next, the trend of dusty days was analyzed and processed using Mann-Kendall and Sense slope in Minitab software.



Results and discussion

The results of analyzing the frequency and determining the minimum and maximum dust occurrences for all stations in the region show that the months of July and June have been associated with the peak of dust occurrences. On the contrary, in most of the stations, the least occurrence of dust has been recorded from November to January. These results indicate the peak of the dust phenomenon in the hot days of the year In terms of the distribution of dust frequency in different observation hours, 09:00 and 12:00 hours were the hours that had the highest dust occurrences in the months of July and June, while 00:00 hours had the lowest number of dust occurrences. The results of the analysis tests of the monthly trend of dust occurrences showed that in the month of January, only at 09:00 at Dezful station, a significant decreasing trend occurred at the 95% confidence level. After that, in the month of December, at 12 and 09, the phenomenon of dust occurred with a significant trend. In other months and by hours in the stations, a significant increasing and decreasing trend has been estimated. Ahvaz station is one of the stations with a significant increasing trend in all observation hours. Only at 21:00 in November, Ahvaz station has brought a significant decreasing trend. On an annual scale, an increasing trend has been observed in the dust of the studied area in all hours.



Conclusion

The general results indicate that the highest number of dust events in Khuzestan province are related to the months of June and July. In these two months, due to the intense heating of the earth's surface due to intense sunlight, surface thermal low pressures occur on the earth's surface. In these months, intense sunlight hits the studied area, on the one hand, it increases evaporation and transpiration, and on the other hand, it causes the surface layer of the soil to become drier, and the soil moisture and, in addition, the air humidity also decrease drastically. The low soil moisture, along with the creation of thermal low pressures in the area, which gives rise to strong winds, has the ability to raise soil particles and create dust storms. The lowest soil moisture and air humidity and the largest thermal pressure difference are related to the hot hours of the day, i.e. 12:00 to 3:00 p.m., and the most dust is observed in these hours. In the early hours of the morning and at night, due to the decrease in temperature, the relative humidity of the air increases, and in addition, the pressure difference, which is the main driver of wind, reaches its lowest level during these hours of the day and night, so the lowest amount of dust is recorded during these hours. Since the main goal of this research was the hourly monitoring of dust in Khuzestan province, its results can be used as an early warning tool for people prone to cardiovascular diseases, children and the elderly and predicted the hours with high risk of dust event.