The effect of changes in climate parameters on the mobility and stability of sand dunes in the watershed of Lake Urmia - Mahabad Station

Studying the mobility of sand dunes and sand dunes in different parts of the world show different indicators of wind erosion and mobility of sand dunes. All of them are based on two factors, which decrease or increase the mobility of sand dunes. The first factor is related to the degree of windiness (W), which is expressed as the annual percentage of days when the wind speed is higher than the threshold speed of sand movement. If the degree of windiness (W) increases, most of the sand dunes become mobile. The second factor on which vegetation growth depends is the ratio between average annual rainfall (P) and evaporation. Potential (PET) is expressed annually. This ratio is also called effective rainfall. The basis of this model is known as the index of mobility of Lancaster sand dunes.
Calculations related to potential evaporation and transpiration, frequency and continuity of the phenomenon of meteorological droughts have been done using the SPEI index, the total of which is 755.98 millimeters per year in Mahabad station, which shows an increasing trend. About 84% of the winds recorded in this station have a speed of less than 6 meters 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%, About 27% of the prevailing winds have a speed of (6-10) meters per second. Meanwhile, less than 1% of prevailing winds have a speed of (10-12) meters. According to the Lancaster index, the mobility of sand dunes in the region is less than 50 in a period of 33 years and they are in an inactive state. There is a direct relationship between the Lancaster index with the percentage of winds above the erosion threshold and the amount of evaporation and transpiration and the opposite relationship with the amount of precipitation. The rate of change of the Lancaster index is the same for the increase or decrease of the percentage of winds above the erosion threshold in Mahabad region. The rhythm of changes in the mobility of the sand dunes of Mahabad region is almost the same with respect to the increase or decrease in the rate of evaporation and transpiration potential of the region; With the difference that the decrease in the mobility of sand dunes with a decrease in potential evaporation and transpiration is greater than its increase rate in the case of an increase in potential evaporation and transpiration. According to the aridity index based on UNEP classification, all weather stations of the province are in a semi-arid to humid state, and according to this, The region is facing a moderate risk of desertification and semi-humid, which threatens its desertification.