Characteristics of Wind Regime and Sand Transport Potential in Coastal Hills (Case Study: Jask)

One of the most important natural processes in arid regions is semi-arid wind erosion. Sand dunes are one of the most important facies of wind erosion. Sand dunes in the field of wind process are among the most dynamic geomorphic features of the earth's surface, which, on the one hand, are affected by the characteristics of speed, direction, wind frequency and, on the other hand, are affected by the characteristics of the earth's surface and sedimentary materials. Probability-based wind prediction for sand transport phenomena is a key element for human activities in arid regions. Wind erosion and movement of quick sands, which is considered as one of the important processes of land degradation and a serious challenge in Iran, occurs due to the interaction between climatic and terrestrial processes. The phenomenon of dust and the movement of quick sands is considered one of the important processes of land degradation and a serious challenge in Iran, and on the other hand, coastal areas are sensitive lands that have been affected by both sea and land ecology. They are also unique in terms of ecosystem diversity. Therefore, knowing the status of wind erosion and the activity of wind sediments, especially in landforms sensitive to this destructive environmental phenomenon, as well as identifying climatic factors affecting it can be an effective step in reducing desertification and improving air quality, especially in arid and semi-arid areas.

According to the purpose of the study, data on wind (frequency and direction), rainfall, temperature and number of dust days related to the synoptic station located in Jask city during a 20-year statistical period (2001-2021) were obtained from the Meteorological Organization. WR-Plot View 7 software was used to analyze the anemometer data. Also, using the mentioned capabilities of the software and considering the basic speed equal to the threshold speed of wind erosion, annual and seasonal storm rose were prepared. Land use maps and sand maps of the study area were prepared using aerial photographs, Google Earth satellite images and field visits.

Statistical analysis of climatic data in Jask region during the period (2001-2021) showed that significant annual changes in annual rainfall, temperature and wind occurred, so that the annual rainfall trend decreased significantly. The trend of annual temperature changes has not been significant, but the temporal changes of wind have taken a relatively downward trend and have shown a significant decrease in recent years. According to the annual windfall of Jask station, it was observed that 7.7% of the total annual observation hours, the air is calm and without direction, 3.92% of the winds blow in different directions and the speed is more than 0.5 m/s. The prevailing wind direction is from the west in all seasons and from the east in summer. The results of classifying the percentage of wind speed frequency showed that about 80% of winds have a speed of less than 6 m/s. The trend of changes in erosive winds during the statistical period under study has an upward trend until 2014 and in recent years has a decreasing trend so that in 2021 the lowest frequency of erosive winds was observed. The results of the portability calculation showed that the annual average of DP is 257 units. The final direction of movement of the sand is at an angle of 280 degrees to the north and the UDI index (RDP / DP) is 0.3, which indicates the variability of low wind directions. The Golmaseh diagram also showed that the wind sediments were moving to the northwest. The highest sand carrying capacity was seen in 2014 and the lowest in 2021. Considering the average of 257 vector units for Jask, the capacity of the amount of sand that can be moved annually is estimated to be about 18 cubic meters per unit width. In terms of land use, most of the area covers the rangeland. Also, sand zones cover about 5.7% of the area, which is mainly located in the south and southeast. The results of the interpretation of aerial photographs, satellite images, as well as field visits to the sand dunes of the southern regions of Iran, indicate the existence of sand dunes of the type of transverse hills, Barkhan and Seif, which are the result of two-way winds from one sector is blowing.

80% of winds have a speed of less than 6m/s, 20% of winds have a speed of more than 6 m/s. The monthly distribution of wind speeds below the threshold indicates that the highest number of erosive winds was observed in summer and the lowest frequency was observed in autumn. The wind direction is dominant throughout the year and all seasons except summer from the west. The amount of sand carrying capacity based on the threshold speed of 6.5 m/s is about 257 vector units moving from the southeast (coastal lands) to the northwest (coastal lands), which indicates that the direction of transfer of most sands from relatively arid and saline coastal areas (coastal grasses) are towards the plains and mountainous lands along the southern coasts of Iran. The ratio of vector to annual algebraic output (UDI) of this station is 0.3, which indicates composite multi-directional winds with sharp angles of variability of wind directions at low levels. Existence of sand dunes of longitudinal hills, seifs and silks is the result of two-way winds blowing from one segment. In the southern coasts of Iran, most of the main winds from the southwest and sub-southeast winds from the coast to the sea are effective in the formation of sand dunes. The strongest winds of the study area blow in summer and the weakest in autumn. The trend of changes in sand transport potential also showed the trend of wind energy in Jask station, which for most years has the ability to carry wind sediments in the middle class (DP> 200> 400), but a significant decrease was seen in 2018 to 2021; the highest sand carrying capacity was seen in 2014 and lowest in 2021. Also in the study station, the RDP/DP ratio has a range of changes between 0.022 to 0.8 in almost all seasons and throughout the year. The area of sandy regions has increased from 72.260 to 82.925 km2 between 2013 and 2021, which shows an increase of 10.66 m2.