The Role of Biological Windbreak in the Creation of Microclimate in Arid Areas of Dehloran, Ilam

In this study, the ENVI-met Headquarter model was used to design a biological windbreak to control wind erosion, and wind tunnel was used to determine the wind erosion threshold. In order to determine the wind erosion threshold, soil samples were transferred to laboratory and exposed to dry air and transferred to wind tunnel. Then, the wind erosion threshold velocity was measured by adjusting the wind flow velocity and using an anemometer. The data required for simulation with Envi-met model include geographical location of the region, soil texture, average minimum and maximum temperature, average minimum and maximum relative humidity, average maximum wind speed and wind direction. Based on the simulation results, both designed windbreak for the Prosopis juliflora and Haloxylon aphyllum species can create microclimate in region. The wind speed decreased to the wind erosion threshold in the Haloxylon aphyllum species windbreak and less than that in the Prosopis juliflora species windbreak. In general, in the Prosopis juliflora species windbreak temperature in the first and last row of the windbreak was 36.12 and 34.78˚C, respectively. Besides, the lowest relative humidity in the first row was 28.52% and reached to 33.11% in the distance of 8h to 10h behind the first row. On the contrary, inside the Haloxylon aphyllum species windbreak, the temperature in the first row was 34.67˚C and in the last row was up to about 35.21˚C. Moreover, the highest relative humidity in the first and last row was 33.28% and 31%, respectively. Therefore, the designed windbreak for the Prosopis juliflora species can protect the more distance behind the initial windbreak, reduce the wind speed to a longer extent from the initial windbreak, more effectively affect the microclimate of the area, and modify it. Thus, it is recommended as a suitable windbreak for the study area.

Wind erosion is one of the major problems in arid and semi-arid regions which occurs mainly in the areas with rainfall less than 200 mm. Following the erosion of the wind, the area is deserted and degraded. The problem of erosion in the arid and semiarid regions is very important, since the compensation for the eroded soils is impossible and difficult due to the unfavorable conditions and the fragile ecosystem. Among the methods used to combat wind erosion, the construction of live and inert windbreaks is a good place to be considered as an appropriate option to prevent damage caused by wind erosion to biological and economic resources. The construction of windbreaks has many positive effects on environmental factors, including the advantages of the Windbreak on the temperature of the soil, air humidity and soil, snow accumulation, evaporation rate, carbon dioxide accumulation, etc. Therefore, considering that Dehloran city has a critical center of wind erosion and is also exposed to dust due to its proximity to Iraq, the current study aims to draw a biological windbreak and figure out its role on the microclimate of the study area investigated using the ENVI-met Headquarter model, which is one of the micro-climatic simulation models of urban climate.

After a detailed visit and the identification of the area, sampling was carried out at the depth of 0-3 cm in three replications. In this study, the threshold wind velocity for erosion was determined using a wind tunnel machine in Ilam University Lab. In order to determine the threshold wind velocity for Erosion, soil samples were exposed to the air in a dry tunnel after being transferred to the laboratory in a wind tunnel. Then, the threshold wind velocity for Erosion was measured with acceptable accuracy by adjusting the wind speed and using the Manometer. The ENVI-met Head quarter was also used to design a biological windbreak. This model calculates the weather conditions (temperature, wind, humidity) at different levels of the domain and the range of effects (buildings, types of vegetation, types of permeable and impenetrable surfaces). Therefore, the most commonly used and used seedlings in sand dunes SStabilization, two Prosopis juliflora and Haloxylon aphyllum species, which are most used in sandy stabilization and flooding projects in the study area, were selected for simulation. The preliminary data required for the implementation of the model is based on the geographical location of the study area, including latitude, longitude, soil texture, air temperature conditions, velocity, wind direction and relative humidity. After implementation of the model, the outputs of the model were prepared and analyzed using Leonardo software.

Based on the results of Table 3, mean Threshold Velocity for Wind Erosion in the study area is 4.84 m/s. According to the simulation results, both designed Windbreak for the Prosopis juliflora and Haloxylon aphyllum species could lead to the formation of microclimate in region, so that the wind speed has dropped around the wind erosion threshold in the Haloxylon aphyllum species Windbreak and less than that in the Prosopis juliflora species Windbreak. In the Prosopis juliflora Windbreak, the region temperature in the first row of the Windbreak is 36.12 ˚C and in the last row of the Windbreak is reduced to 34.78 ˚C. The relative humidity of the area in the first row of the Windbreak was 28.52%, and of the last row reached 32.55%. On the contrary, in the Haloxylon aphyllum Windbreak, the temperature of the region in the first row of the Windbreak was 34.67 ˚C, but in the last row of the Windbreak increased about 35.21 ˚C, although the relative humidity of the area in the first row of the Windbreak was 33.28% and decreased to 31% in the last row. However, at the end, it can be said that designed windbreak for the Prosopis juliflora species can protect more distance behind the initial windbreak, reduce the wind speed to a longer extent from the initial windbreak, more effectively affect the microclimate of the area, and modify it. Based on the results, it can be said that the changes in temperature and relative humidity in the Prosopis juliflora contrary is a Haloxylon aphyllum species. This difference seems to be due to how the wind velocity changes in the two windbreak, which is the speed change itself to the height of both windbreak, because the higher the wind speed, the lower the wind speed. Therefore, in a Prosopis juliflora windbreak, with a further reduction in wind speed and air turbulence in the vicinity of the surface of the soil and the creation of shadows, there is a region with relatively moderate, relatively low temperatures. As a result, with decreasing air temperature, the amount of evaporation decreases and consequently the amount of moisture increases.

Considering that all three factors of wind speed decrease, temperature decrease and humidity increase can reduce evaporation from the water surface. Therefore, in addition to reducing wind erosion in sand dunes and road sides, Prosopis juliflora species can be used as a suitable type for windbreak construction in order to reduce the evaporation from very limited water resources located in the windy region.