عنوان مقاله [English]
One of the factors influencing the changes in the morphology of desert areas is the frequency of wind blowing due to the relative poverty of wind blowing and the surface and covering cover in these areas. Wind transport of sand is a complex process that depends on factors such as wind speed, amount of bare soil, dry air conditions, soil grain size, vegetation, local and external air system, short-term discharge, extent of deforestation, in an area. Based on this, the activity of winds in carrying out erosion is significantly related to the climatic conditions of each region. Wind erosion in desert areas is seen in the form of sand dunes.The importance of sand dunes studies is due to their impacts on water and soil resources, flora and fauna, human infrastructure, and roads. Therefore, for the purpose of basic planning, monitoring the speed and direction of movement or the expansion of sand dunes, due to the damages caused by it and especially the preservation of natural resources and human projects and facilities, is of special importance in the management of desert areas.
In this research, wind characteristics, dust characteristics, soil moisture and its effects on Zabol region are investigated. To check wind speed and direction, the data of Zabol anemometer station were evaluated in Wrplot software. Then, the sand graph was drawn in SandRose-Graph software in order to check the indicators of sand movement. The changes of dust and AOD index of the region were extracted in the Erthengine system and MODIS satellite images in the period from 2012 to 2023. Changes in soil moisture index in the region were also monitored using SMAP satellite images in Arth Engin.
Results and Discussion
In this research, the predominant wind direction of the region was determined as northwest-southeast by examining the wind direction of Zabol station. On the other hand, examining the trend of wind speed changes at Zabol station shows that the average wind speed at Zabol station has been increasing over the past 56 years; So that the average wind speed has reached from 2.5 m/s per month in 1962 to about 4.8 m/s per month in 2018, which shows an increase of 2.3 m/s during this period. The amount of sand carrying potential (DPt) at this station is 2079/8, which is estimated to be high based on Freiburger's and Dean's classification of wind energy at this station. The variability index (UDI) of wind directions for Zabol station is in the low variability group with the classification of unidirectional and channelized winds, which greatly increases the intensity of erosion and dust production. The highest amount of displaced sand (DSF) in Zabol station indicates the amount of sand particles transported in the region.
In addition to examining the characteristics of the wind in the region, the changes in the dust index (AOD) and aerosol were also carried out using MODIS sensor images in the environment of Erth Engin from 2012 to 2023, and the results showed that the highest percentage of dust with a size greater than 55 microns and less than 47 microns in the summer of every year and with the decrease in surface humidity and the increase in temperature and the occurrence of 120-day winds in Sistan, also the examination of the percentage of dust changes in the air in the 5-year period from 2018 to 2023 showed a significant increase. which indicates an increase in the percentage of airborne particles due to the expansion of wind erosion in the region.
Next, the soil moisture of the region was monitored using the Smap satellite image series, including changes in the percentage of surface and subsurface soil moisture in the Zabol region in the Google Earth Engine environment and the time period from 2015 to 2023, and the results showed that the highest percentage of soil moisture is from February to April. And the lowest percentage of soil moisture is from July to September, which corresponds to the occurrence of 120-day winds in Zabol region.
The results obtained from this research show that the main cause of dust occurrence in Zabol region is the increase in the wind speed in the region in the long term and the increase in dust supply centers around the region, which, along with climate change and the decrease in rainfall and the occurrence of drought, in the scale Locally, the drying up of Lake Hamon as a result of the Afghan government's non-compliance with the 1351 Kabul agreement regarding the introduction of 850 million cubic meters of water per year into Lake Hamon has had a significant impact on this issue. Considering the location of the dried Hamon lake in the northwest and west of Zabol city, and the direction of the prevailing wind, it can be said that most of the dust particles transported to Zabol originate from this area. Therefore, the only solution to the current situation of Zabol can be the restoration of Lake Hamon and stabilization of the sediments on the bottom of Lake Hamon. On the other hand, the presence of channelized and dominant northwest-southeast in the region has provided the conditions for the construction of wind power plants in this region, considering the criticality of the country's energy, which is used with proper planning and investment for this issue.