Document Type : Research Article
Authors
1
Ph. D student in Climatology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
2
Associate Professor of Climatology in Shahid Beheshti University, Tehran, Iran
3
Postdoctoral Researcher of Climatology, Ferdowsi University of Mashhad, Department of Geography, Mashhad.
Abstract
Dust is a common meteorological phenomenon in arid and semi-arid regions of the world, which is caused by natural or human factors. The frequency and intensity of dust has increased in the last two decades. Identifying the active sources of dust is the first step to dealing with it and reducing its harmful consequences. For this purpose, two indices of aerosol optical depth (AOD) and the normalized difference vegetation index (NDVI) from the moderate resolution imaging spectroradiometer (MODIS) sensor of the Terra satellite have been used for the last two decades (2001-2021). To investigate dust springs in the study area, the frequency of occurrence of aerosol optical depth (FoO) was investigated with three thresholds of 0.3, 0.5, and 1. The maximum AOD values are related to the spring and summer seasons. Regions with an aerosol optical depth of more than 1 are only limited to the warm period of the year and the areas of Mesopotamia region, Arabian deserts, desert areas of Syria, Dasht-e Margo and Dasht-e Sistan, and eastern Pakistan. The nationwide dust that covers wide areas in Saudi Arabia and the Persian Gulf countries and the west and southwest of Iran are mostly more than 0.5 in terms of AOD concentration. In general, six hotspots of dust can be identified based on the values of the AOD and FoO index for the West Asian region. These six regions are 1- Thar desert in Pakistan, 2- Rub' al Khali, Ad-Dahna, Al Nufud Al Kabirdesert in Saudi Arabia, 3- the Syrian desert, 4- the Desert regions of Iraq and especially the Mesopotamia region, 5- Dry and desert regions of Oman, 6- Dasht-e Margo and Dasht-e Sistan (in Afghanistan and Iran). These dust hotspots are found in arid, desert, and hot climate regions (BWh). The only effective hotspots in northeastern Iran are located in the arid, desert, and cold climate region (BWk) in Turkmenistan. In general, dust hotspots have an inverse relationship with vegetation, although this relationship is more for hotspot springs. Regardless of the determining role of surface characteristics in the occurrence of dust, two meteorological phenomena, the summer Shamal wind and the wind of 120 days of Sistan, have a determining role in the formation of hotspots with higher AOD values of 0.5 and 1. The area-averaged time series of MOD04 product values showed that the concentration of AOD is increasing. Also, the results showed that the increase in AOD values from the 2010s onwards shows an increase compared to the 2000s. The dry bed of lakes and alluvial sources (Mesopotamia), human activities on the one hand, and the occurrence of drought and climate change, on the other hand, are directly related to the extent and intensity of dust in West Asia.
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