جستجوی مقالات مرتبط با کلیدواژه « کانون گرد و غبار » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

This study investigates and analyzes the decades of change in climatic zones in Karkheh, Karoun, and Zohreh - Jarahi watersheds. For this purpose, the database of temperatures and precipitation networks during the period 1976-2015, with a spatial resolution of 15 x 15 km, formatted in the conical Lambert image system, was used. In fact, because these two elements are the most important climatic drivers in the study area and the changes of other elements in these two elements are more visible, they have been used to study and analyze the climate change zone. After establishing the database, cluster analysis was used to identify climatic regions, and the audit analysis was used to validate it. Cluster analysis was performed on 52 indices of temperature and precipitation (monthly and annual average, coefficient of variation of temperature, and precipitation monthly and annual changes) during different periods, and climatic zones and their changes were analyzed. Based on the results, three climatic zones including humid and moderate zone, hot and dry zone, and very hot and dry zone were identified in the study area. The results showed that in recent periods, the humid area, in addition to having spatial displacement, its area reduced so that in the fifth period, the area reached less than five percent. Also, the hot and dry zone, stretched as a strip from the northwest to the southwest of the study area, had less spatial displacement, unlike the humid area, while its area increased in recent periods. On the other hand, the area of the very hot and dry zone has increased towards recent periods. Spatial and temporal increase of hot and dry climates and very hot and dry climates and decrease of the humid zone has been able to lead to the development and intensification of dust source, especially downstream of the studied watersheds.

Wetlands are an integral part of the semi-arid and arid ecosystems, which are inundated during major floodings and are transformed into sources of particulate matter during drought. This phase of their life cycle is very disturbing as they affect breathing in downwind areas and result in many pulmonary diseases. Thus their management is very challenging. As the Mansuriyeh Wetland (MW) is transformed into a dust source when dry, and threatens the City of Ahvaz with dust storms in the lean years, and this is mainly caused by an eradication of the vegetative corer, it was decided to survey the area when the MW was brimmed with floodwater. This was achieved benefiting from the images collected by the Landsat TM, ETM+ and DLI during the June of 1988 through the same month in 2017, and the rainfall data provided by the National Meteorological Organization. Analysis of the information was carried out in three steps: preprocessing, preprocessing and post preprocessing using the support vector machine (SVM) along with the ENVIs software. Likewise the image were classificed into the inundated areas the land covered with vegetation, water and the bare land. Truthfulness of the image was validated through Google Earth employing the total accuracy and the kappa procedures. The percentage of the area covered by each class was determined through the GIS zooning. The area contributing water to the MW was determined as its watershed, the rain-gauging network was plotted on the maps, and the mean annual precipitation of the entire watershed was calculated and drought occurrence and its intensity were determined using the standard precipitation index (SPI): the R2 for this item was 0.6. Therefore, variation of the MW as a dependent variable is related to the drought as an independent variable. Thus drought is 60% responsible for dust formation. Other variables, namely numerous small earth banks, oil well drilling installation and agricultural activities may also contribute to dust formation. Variations in the extent of the bare area and its relationship with the dust formation indicated that 80% of the MW had dried during the previous10 years. Moreover, up to 100% of the area had been entirely without a vegetative cover in some of those years. Salinity of a fine- grained soil, also made it a potential source of dust storms that invaded the Ahvaz Metropolis.