Journal of Spatial Analysis

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Potential dangers of drought in Shadegan wetland and Identify areas affected by dust from it
 
Introduction
Shadegan wetland is located at the end of Jarahi watershed. This wetland is one of the most important international wetlands registered in the Ramsar Convention, which is currently undergoing ecological changes and is still on the red list of the Montero Ramsar list. This wetland is extremely important due to its high biodiversity and various functions such as flood control, air conditioning and soil erosion control, habitat of various plants and animals and providing livelihood for a part of human societies. One of the most important functions of the wetland, according to the findings of the present study, is the important role of Shadegan wetland in preventing the production and control of fine dust. There are 143 wetlands in Iran, of which 25 are registered in the Ramsar Convention. Shadegan wetland is one of the wetlands of Ramsar Convention, which in the last decade, a large area of ​​it has become dry and has become a center of dust. In this research, it is important to know that in case of drying of Shadegan wetland, which areas in which seasons will be more affected by dust due to atmospheric currents.
Data and methodology
In this study, the boundary of the wetland was determined based on the highest water advance line during a 30-year statistical period (1988-2017). According to satellite images, the border of the wetland has been determined to be about 164,000 hectares based on the rainiest year and month. Wetland area changes were used to monitor the water level of Shadegan Wetland through Landsat TM, ETM + and OLI satellite data from 1998 to 2017 in the period of June. Three stages of preprocessing, processing and post-processing were performed on the images and supervised classification by support vector machine (SVM) method was used and the images were classified into three classes of water, vegetation and without cover or soil. On the other hand, the classification accuracy for the images was calculated using two indicators, overall accuracy and kappa. To calculate the dry area of ​​the lagoon, floor changes without cover were calculated. The most important cities around Shadegan wetland, which in case of wetland drought may be most affected by wetland dust due to proximity and proximity, and have socio-economic importance and the center of the province and port status, were identified. In this study, the cities of Ahvaz, Abadan and Mahshahr were identified and studied as areas affected by wetland dust during drought. In order to study the role of drying of Shadegan wetland in the dust of the surrounding areas, seasonal and annual dust mites were prepared and drawn. Data on the direction and speed of hourly winds along with the dust were used. Then, using WR-PLOT software, in addition to the annual long-term total rainfall, the seasonal distribution of the direction and speed of events was extracted and the rainfall related to each season was plotted and analyzed, and areas affected by drought in different seasons of the year. Wetlands with greater impact were identified.
 
Result
The trend of 30-year changes in the soil cover of Shadegan wetland is increasing in total, so that according to the freshwater area of the wetland, which was obtained in this study 164 thousand hectares, 22960 square kilometers has been added to the dry area of the wetland during these 30 years. The largest soil area of the wetland in 1994 was about 87.4% of the total area of the wetland. The lowest soil area of the wetland in 1998 was about 19%. Sugarcane projects have entered the wetland from the north of Shadegan Zahab Wetland since 2002, but due to widespread drought, it has not been able to increase vegetation and reduce the soil area of the wetland.
During the long-term statistical period, spring is the predominant period of pollination in Ahvaz western synoptic station and secondarily in the northwest. The southeast direction is of third importance, but nevertheless, the dryness of the north and northeast parts of the wetland can affect the south and southeast of Ahvaz in this season in Abadan synoptic station. Drought on the west side of the wetland is not a threat to the city of Abadan. In Mahshahr synoptic station, the predominant direction of long-term seasonal rainfall is northwest. In case of drought, Shadegan wetland will be affected from the northwest. During the long-term statistical period, the summer season was dominated by dust and affected in three stations, such as the spring season, with the difference that in this season, dust is more abundant. During the long-term statistical period, autumn is the predominant direction for flowering and is affected in three stations such as spring and summer, but in this season, the southeast and south directions are more intense and frequent than spring and summer.
During the long-term statistical period, winter is the predominant period of pollination in Ahvaz synoptic station, west and secondarily, northwest. The southeast and south directions are of third importance, but in this season, the southeast and south directions are more intense and frequent than other seasons. In this season, due to the expansion of the westerly wind to the lower offerings, unstable atmospheric systems enter Khuzestan from the south and southeast and bring dust with them from areas such as western and southern Iraq and northern Saudi Arabia, and to the southeast. Northwest and passing through the dry parts of the lagoon and the active dust center of the southeast of Ahvaz, the metropolis of Ahvaz will face problems caused by dust in this season. Due to the cold weather and the inversion phenomenon, the dust of this season, which is associated with wetland and inland resources, has a greater impact on the field of view and causes great damage to the equipment and infrastructure facilities by subsiding on the city of Ahvaz.
Conclusion
Drying of wetlands due to various climatic or human factors can lead to increased dust activities. When a wetland dries out, the salts that settle in it become sources of dust. Wetland fine-grained sediments with air velocity less than the erosion threshold due to small diameter and large volume enter the air streams and are dispersed in the air. Active dust centers in the southern half of Khuzestan province have the largest area in the whole country. Shadegan wetland is bounded on the north by the dust center of the south and southeast of Ahvaz with an area of ​​185043.3 hectares and on the west by the center of the south of Horalazim and north of Khorramshahr with an area of ​​258916.4 hectares and on the east by the dust center of Mahshahr - Omidieh Hindijan with an area of ​​254654.4. Shadegan wetland joins the southeastern center of Ahvaz in case of drought from the north and northeast, as if parts of it, known as Hor Mansoureh, have become part of the southeastern center of Ahvaz in the last decade due to several droughts. Is. From the west, parts of it are connected to the dust center north of Khorramshahr and join it if the drought continues. It is connected to Mahshahr-Omidieh and Hindijan centers from the east. In recent years, parts of the wetland and dust centers have overlapped. If the wetland continues and dries, for natural and managerial reasons, more parts of the wetland will dry up and become dust centers and affect important population, political and port cities of Khuzestan Data and will face irreparable social and economic losses.
 
Keywords: Dust center, dust, wind direction and speed, Shadegan wetland, Right of water