فهرست مطالب m. khosroshahi

Biological operations to combat wind erosion must be carried out in the calm bed of dunes, which is often challenging due to high-velocity winds. Therefore, the necessary precondition for stopping the movement of sand is to create obstacles in the path of their movement, protecting newly planted vegetation from wind damage and ensuring stability during the initial years. In this project, various methods of preventing wind erosion, including creating a windbreak to reduce wind speed below the erosion threshold and sand spraying to increase the wind threshold, were evaluated in the dunes of Abuzidabad, Kashan, under severe wind erosion. The windbreaks used include mesh with a percentage of 50% porosity in a checkerboard with dimensions of 2.5 * 2.5 m, and cottonwood harvested from cotton fields in a grid of 5 * 5 meters. The height and distance of the windbreaks were calculated using the wind threshold speed and the maximum wind speed of the region. Sand spraying was tested on dunes and clay-salt panes with 50% and 30% density. To compare the rate of soil displacement in the above and control treatments, graded wooden indicators up to a height of one meter of sediment traps were used. In addition, the effect of net windbreak on the percentage of successful establishment of the Holoxylon sp. plant compared to the control was investigated. In this study, the cost of each method was calculated separately and compared with the cost of spraying oil mulch. The results showed that 50% sand spraying, in addition to having the best performance in stabilizing sands and preventing the formation of dust, as well as stability, also has a lower implementation cost than other methods. Therefore, the 50% sand spraying method is introduced as the best method to stabilize and prevent erosion at the lowest cost and also environmental compatibility.

Improving vegetation cover in arid and semi-arid regions can be controlling desertification and the production of cellulosic materials by afforestation, in these circumstances, human survival and habitat, as well as wildlife, also provided too. For afforestation in arid and semi-arid regions, it is necessary to selection of appropriate species and pay attention to their ecological and eco adaptation needs. Drought resistance mechanisms include water use efficiency in many forest species for a stay of drought condition have been utilization. On the other hand, water requirements and the effects of drought stress on ecological adaptation are important for this plants. Through lysimetry experiments and determination of water requirement for many forest species including Saxual (Haloxylon aphyllum) and several species of eucalyptus (Eucalyptus camaldulensis, E. microtheca E. sarjentii, E. leucoxyloni, E, saligna and E. flocktoniea), there were considered and adaptation mechanisms for survival in dry conditions were studied for them. Among the mentioned species, Saxual had the lowest water requirement and the most resistant species to drought stress. This species had a higher water use efficiency to drought stress.

Dams, as massive hydraulic structures, widely affect the flow of rivers downstream. Assessment of the extent of this impact is one of the most important issues in flood control research. In the present study, the annual and flooding trends of the Jarahi River and the relationship of these changes with the establishment of Maroon Dam was investigated. For this purpose, the diagrams of annual average discharges and flood peak discharges in two hydrometric stations of Idnak (upstream of the dam) and Behbahan (downstream of the dam) were plotted and a pairwise t-test (in SPSS software) was used to analyze the difference. The maximum flow discharge of Jarahi River was used in a period of 17 years before and after the operation of Maroon Dam. The results show the effect of Maroon Dam on peak flood discharges; In the 17-year period after the date of the opening of the Maroon Dam, the peak flood discharges in the downstream station of the dam compared to the 33-year period before that, have decreased significantly (88.9% decrease after Since the opening of the dam). The average maximum flow rate in the two mentioned periods before and after the construction of the dam is 1757.9 and 194 cubic meters per second, respectively, which indicates that the Maroon Dam has restrained the flood peaks. The statistical test also shows that no significant difference between the maximum flood discharge before and after the opening of Maroon Dam is observed in the hydrometric station upstream of the dam; however, at the downstream hydrometric station, a significant difference of 1% is observed between the maximum flood discharges before and after the opening of the Maroon Dam. Also the average annual discharges were coincided in a decreasing trend, given the trends in the two upstream and downstream of the dam, which can be attributed to drought occurrence and climate change.

The occurrence of wind erosion and the spread of dust particles can be regarded as one of the most important and threatening environmental factors. Climate change and the frequency of droughts have played an important role in exacerbating or weakening these events. The primary objective of the present study was to investigate the trend of changes in four important climatic elements (precipitation, temperature, wind speed and relative humidity) and dust storm index (DSI) in Qazvin city using the Mann-Kendall pre-whitened test and to determine the relationship between them based on the multiple linear regression method. Assessment of the meteorological drought status based on two standardized precipitation index and standardized precipitation, as well as the evapotranspiration index and analysis of their effect on activity level of dust events, was the other objective of this study in the study area. For this purpose, after preparing and processing the climatic data and calculating the dust storm index, the trend of changes and the relationship between climatic parameters and dust events were investigated. The results showed that the changes of trend in the annual precipitation and relative humidity in Qazvin city were increasing, while the trend of annual changes in the wind speed and the mean air temperature was a decreasing one. Investigation of the monthly changes in the dust events also showed that there was a sharp decrease in the occurrence of wind erosion and the spread of domestic dust particles only in July. On a seasonal scale, with the exception of winter that has been reported without trends, in other seasons, the intensity of these events was significantly reduced. The effect of the meteorological drought on wind erosion was estimated to be 11% at the confidence level of 99%. In general, these findings indicate a decreasing trend of land degradation and desertification caused by wind erosion in Qazvin.