تأثیر تغییرات سنجه‌های اقلیمی بر تحرک و پایداری تپه‌های ماسه‌ای در آبخیز دریاچة ارومیه، ایستگاه مهاباد

Introduction and Goal
Sand dunes with their unique system can be mobile or stable, and the main factor influencing their stability is the presence of vegetation cover. The unique characteristics of sand dunes and their high hydraulic conductivity increase the rate of rainwater infiltration. With the drying of sand particles and the loss of cohesion between grains, weak vegetation and wind erosion will occur. Considering the new climatic conditions prevailing in the areas surrounding Urmia Lake, the aim of this research is to identify and examine the new sand dunes and their movement trends in these regions. Therefore, due to the absence and their formation at the provincial level, only the Mahabad meteorological station was examined regarding wind conditions and the Lancaster index.
Research materials and Methods
In this research, to examine the effect of climate changes (wind and precipitation) on sand activity and to predict the likelihood of mobility of sand dunes and sand fields, as well as the dust generated from them, the global Lancaster method was used. Based on the Lancaster index, the relationship between sand mobility and climatic variables was modeled. Then, sand and dust particles move following winds with speeds exceeding the erosion threshold, which has an inverse relationship with effective precipitation. Therefore, the necessary data including precipitation statistics, temperature, wind, and relative humidity of the Mahabad station were obtained from the Provincial Meteorological Organization. Also, in order to determine dry and wet years and their effects on the increase or decrease of dust days, the SPEI index was used. Potential evapotranspiration, frequency, and continuity of meteorological droughts can be calculated using the SPEI index. To determine the climatic status and the risk of desertification, the aridity index (AI) was used. Considering the precipitation and potential evapotranspiration measurements, the aridity index was calculated using the Torrent-White method, and the desertification status of the region was determined according to the UNEP classification. This index is an effective tool for determining the climatic status and desertification risk of various regions.
Results and Discussion
In this research, using the SPEI index, data on potential evapotranspiration, frequency, and duration of meteorological drought events were collected. The results showed that the total potential evapotranspiration at the Mahabad station was 755.98 mm per year, with an increasing trend. About 84% of the winds recorded in this station have a speed of less than 6 m per second. Meanwhile, the concentration of the strongest observed winds is in the months of (Mar), (Feb) and (Apr) with 12.1, 11.2 and 10.1 percent, respectively. Additionally, 27% of the prevailing winds had speeds between 6 to 10 meters per second, while less than 1% of the prevailing winds had speeds between 10 to 12 meters per second. According to the Lancaster index, the mobility of the existing sand dunes in the area over a 33-year period was less than 50, indicating that their status was inactive. The relationship between the Lancaster index and the percentage of winds exceeding the erosion threshold was direct, while it was inverse with the amount of precipitation. In the Mahabad region, the rate of changes in the Lancaster index in relation to the increase or decrease in the percentage of winds exceeding the erosion threshold was equal. The mobility of the sand dunes is a function of changes in potential evapotranspiration in the area and has a direct relationship with it. Therefore, with an increase in potential evapotranspiration, mobility also increases. The aridity index obtained, according to the classification provided by UNEP, showed that all meteorological stations in the province are in a semi-arid to humid status. Consequently, the Mahabad region faces a medium risk of desertification, which threatens its semi-humid status.
Conclusion and Suggestions
Based on the studies conducted in West Azerbaijan Province, areas with significant sand dunes or those currently forming have not been reported so far. However, during visits to the shores of Lake Urmia and within the boundaries of Mahabad County, small signs of sand dune formation were observed, which disappeared a year later due to being within the range of annual water level fluctuations of the lake and the flow of water from the surrounding shore. In this study, while recognizing the trend of changes in climatic elements and the correlation between these factors as independent variables, the possible effects of climate change on the dust phenomenon and the mobility of existing sand dunes have been investigated. In all statistical years, the mobility of existing sand dunes in the region was less than 50 and the Lancaster index obtained for the Mahabad synoptic station showed an inactive state. Also, based on the sensitivity analysis of the Lancaster index, the decrease in the mobility of sand dunes with a decrease in the potential evapotranspiration was greater than the rate of increase in mobility under conditions of increased potential evapotranspiration. Based on the UNEP index classification, the Mahabad region has a semi-humid aridity index with the lowest level of evapotranspiration, facing a medium risk of desertification. Therefore, considering the prevailing climatic conditions, it is recommended to be extremely careful and sensitive in land use and to use optimal irrigation methods in agriculture and drinking.