jebraeel ghorbanian

Dust events are one of the most important and challenging environmental and climatic hazards of the whole country and especially of Khuzestan province. The main goal of this research is to reveal the role of changes in vegetation cover and soil moisture in the annual distribution of dust events in Khuzestan province. In this regard, 3 categories of data were used. The data related to station dust codes obtained during the statistical period of 2010-2020 for the synoptic stations of Khuzestan province on an hourly scale. The second set of monthly vegetation data was obtained from the NDVI product (MOD13C3) of the MODIS sensor, and finally, the moisture data of the upper 5 cm layer of the soil was provided from the SMAP sensor on a monthly basis. By analyzing the frequency of dust codes, the monthly frequency of dust events, the concentration and persistence of dust were investigated. By obtaining the spatial average values of the two moisture indices of the upper 5 cm soil layer and the monthly NDVI index, the correlation and relationship between the dust indices and these indices was analyzed. The results showed that based on the average period of 2010-2020, the period of 4 months from May to August is the dust peak period in the province. There are at least 11 days of dust in every month, and the concentration of dust is more than 2800 micrograms per cubic meter in the air, and the duration of the dust event in the province is at least 40 hours. The investigation of the moisture indicators of the upper layer of the soil and vegetation showed that, exactly in the province during the same dust peak period, the soil moisture of the upper layer of the soil reached less than 10% in a large part of the central and southern regions of the province, and at the same time, the vegetation index also In these sectors, it has reached less than 0.18. In addition, in this research, it was observed that the monthly changes in the moisture content of the upper 5 cm layer of the soil with a correlation coefficient of -0.88 have the greatest effect on controlling the dust concentration in Khuzestan province.

Extensive and massive agriculture, along with other agricultural activities such as animal husbandry, industrial activities in the southern half of the province, has created and intensified extensive changes in the environmental resources and natural structure of the province. This extensive change can show its effects and consequences in the destruction of forest lands, the transformation of rich pastures into poor pastures and barren lands, severe soil erosion, and finally the creation and development of internal centers of dust. and intensify the severity of dust incidents in the province. Dust events have profound and significant effects on agriculture and soil fertility, health and hygiene, disruption and destruction of industries and power plants, and negative effects on the environment, including the deterioration of forests. Airborne particles, which are mainly driven to the region by dust storms, are one of the important components of the atmospheric system. They can not only change the albedo of the energy balance by acting as cloud particle nuclei, or ice nuclei.

The study location of this research is Khuzestan province, which is one of the most challenging provinces in the country in terms of environmental hazards. This province, with an area of about 6.5 million hectares, occupies about 4% of the country's area. Dust is one of the major and most important challenges of this province. Its destructive effects can be traced in various dimensions, such as the quality of water resources, the quality and performance of agricultural products, industries and energy transmission networks, and the air quality of cities. Three categories of data have been used in this research. The data of the first category is related to the data of widespread dust days in Khuzestan province. These data were obtained from the dust codes of the current air condition (ww parameter of synoptic stations of the province) during the statistical period of 2000, 2020. The second category of data was actually the remote sensing data of MODIS sensor, which included the Aerosol Optical Depth (AOD) product of MODIS sensor (MOD04 product) and Aerosol Exponential Index (AEA). These two indicators are dimensionless but with different directions. In the AOD index, higher numbers represent more aerosols in the atmosphere and in the AEA index, in addition to the presence of dust in the place, it also provides the size of the aerosol particles. Finally, the third category of data is the reanalysis data related to incoming net shortwave radiation (SNSR), which was taken from the reanalysis data of the European ECMWF database version ERA5 with a spatial resolution of 0.5 arc degrees. 

In this research, it was tried to investigate the influence of the dust event in the context of fluctuations and daily changes in the amount of net shortwave radiation received on the earth's surface. The results of the investigation of three cases of widespread dust in the province showed that in these three cases of widespread dust, aerosol particles are generally in the central, southern and western parts of the province (plain and lowland areas of the province) from the type of medium to large particles (index angstrom between 0.5 and 1) and in the eastern and northeastern parts, it was of the type of coarse particles (angstrom index less than 0.5). In the context of the impact of dust events on the amount of shortwave radiation received by the earth's surface, it was seen that in the dust event of July 22, 2010, the Angstrom exponential index indicates the presence of coarse particles in the atmosphere near the earth's surface and the AOD index also indicates the presence of dense dust in the entire area of the province. The received net shortwave radiation (at 12 noon or 09 UTC) was about 194 watts per square meter (about 28 percent) lower than the average for the same month. This drop rate was less in the other two dust waves, whose AOD and Angstrom index values indicated finer and less concentrated dust. In the dust wave of June 19, 2012, the amount of net shortwave radiation received was only 5% (25 W/m2 at 12 noon or 09 UTC) less than the long-term average, and this drop in the dust event of May 12, 2018 was equal to 28 W/m square (about 4% drop compared to the average of the same month).