Determining the Role of Different Climatic Factors in the Occurrence of Internal and External Dust in Ahvaz Metropolis using Neural-artificial Network

In addition to domestic dust sources, Ahvaz city is affected by most of the foreign sources of dust which is mainly due to locating in the passage of southeast-northwest winds and vice versa. In this study, internal and external dusts were separated to determine the role of climatic factors in the occurrence of dust in Ahvaz. Therefore, the data related to parameters and climatic phenomena affecting the occurrence of dust have been used. Besides, the analysis and comparison of different neural networks have been applied to figure out the importance of each climatic factor in the occurrence of dust. In this study, 70% of the data are entered the network as educational data and 30% as test data. The square sum of educational data error and test data, the relative error of educational data test data and also the correlation coefficient between the measured and estimated values have been compared to evaluate the accuracy of different functions. Finally, the model showing the lowest error rate and the highest correlation coefficient has been selected as the optimal model to investigate the contribution of climatic factors affecting the occurrence of internal and external dust. The results show that wind factor with a speed of more than 6 meters per second and then the wind less than 6 meters per second have played the most important role in the occurrence of internal dust. Moreover, rainfall-changes factor is the third effective one. In the case of foreign dust, since Ahvaz is influenced by the conditions of more remote areas that are almost outside the political borders of Iran, drought factors, SPEI and DTR indices, are considered as the important factors in the occurrence of regional widespread dusts that reach Ahvaz.
Extended Abstract
1-Introduction
Dust is a common feature of the dry areas or any area that is adjacent to dust sources. These areas are affected by consequences of dust due to being located in the passage of dust systems. Dust can be transmitted to other regions, harm human health and affect the global climate. Numerous studies have examined the role of climatic factors in the occurrence of dust. In most of these studies, several parameters or climatic indicators and their roles have been studied, although the impact of all parameters and climatic factors, and their contribution to the occurrence of dust on the occurrence of dust have not been modeled yet. Several factors affect the occurrence of dust in Ahvaz. The role of climatic factors, as a driving force of dust particles, has an important role in producing and intensifying the incoming dust to Ahvaz metropolis as the largest population city in the region with macroeconomic importance. Recognizing effective dust sources in this metropolis will help planners and decision makers to control and control dust in operational plans and reduce the effects.
2-Materials and Methods
The current study aims to identify the number of dust events, whether inside or around the station (internal) or out of the station (external), and to determine the role of climatic factors in their occurrence, hourly synoptic statistics (every three hours). Therefore, dust monitoring codes related to Ahvaz synoptic station during the statistical period of 1958-2018 have been used. Statistics related to other parameters and climatic phenomena affecting the occurrence of indoor and outdoor dust such as are applied including average temperature, average maximum temperature, average minimum temperature, rainfall, evaporation, minimum and maximum relative humidity, total occurrence of winds, winds less than 6 meters, winds more than 6 m/s and climatic indicators such as effective precipitation, SPEI drought index (standard precipitation and evapotranspiration index), DTR index (temperature difference between night and day) and days with precipitation during 61 years. In addition to identifying the trend of changes in dust with internal and external origin, the current study aims to determine the importance of each factor affecting the occurrence of internal and external dust in Ahvaz metropolis by applying neural networks, multilayer perceptron and radius circuit functions.
3-Results and Discussion
In the occurrence the dusts with internal origin, the winds with the speed more than 6 meters per second have been identified as the most important factor affecting the occurrence of dusts, since in the case of dusts around the station the wind speed must reach the erosion threshold to make particles separate from the ground and enter the atmospheric currents. In the occurrence of dusts with external origin, wind threshold begins in the origin emitting the particles into the atmospheric currents which makes them enter the region in the bed of synoptic currents. This phenomenon leads to reducing visibility and reporting of dust in the region. In most cases, due to the decrease in wind speed compared to the origin, Ahvaz turns to be a particle-subsidence area in most cases. The second important factor is the winds with the speed less than 6 meters per second.  The third factor is the decrease in the number of rainy days which leads to drying of soil and reducing vegetation, resulting in favorable soil bed and preparation of fine sediments in focal areas. Therefore, the particles will rise from the ground even at wind speeds below the erosion threshold.
In the occurrence of dusts with foreign origin, the SPEI climate drought index has the most highlighted role. The second important climatic indicator in the occurrence of dusts with foreign origin in Ahvaz is the changes in the DRT index or the difference between day and night temperatures. The third factor is the number of rainy days. Since these days are regional, external dusts decrease. Next factor is the wind with less than 6 meters per second. In fact, as the wind speed decreases, dusts with foreign origin have a subsidence in Ahvaz.
 4-Conclusion
Among all the provinces of Iran, Khuzestan province, especially Ahvaz metropolis, is recognized as the most critical region facing the challenge of dusts. The findings from Heydarian et al. (2014) reveal that 9% of the Khuzestan plain area, equivalent to 349,254 hectares are the source and center of dust production. Due to the increase in continuous droughts, the area of internal dust centers has been estimated to be about twice, 741489 hectares, by the Geology and Mineral Exploration Organization of Khuzestan. Therefore, identifying and adjusting climatic conditions in the areas prone to dust production have a great role to determine the abundance, persistence and intensification of dust. The study area in this article and the dust centers affecting it are located in arid and semi-arid regions, as the intrinsic characteristics of these areas have sensitive and fragile conditions to climate change which may affect human activities, especially in the last two decades and in the future dust phenomenon is always a major challenge. The control of climatic factors is beyond the control of humans, although it is possible to control and reduce the damage to some extent by taking appropriate suitable.