Climatology
Soodabheh Namdari; Ali Hajibaglou; GholamReza Abazari
Abstract
IntroductionAtmospheric mineral dust particles play a key role in the radiation budget of the atmosphere and the hydrological cycle, and have an important effect on public health by disrupting climate systems and air pollution. Due to Iran’s location in the arid and semi-arid belt of the world, ...
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IntroductionAtmospheric mineral dust particles play a key role in the radiation budget of the atmosphere and the hydrological cycle, and have an important effect on public health by disrupting climate systems and air pollution. Due to Iran’s location in the arid and semi-arid belt of the world, Iran is constantly exposed to local and regional dust systems. Considering the importance of the negative effects of dust storms and their increasing trend in some dust sources, the study of these changes in the last two decades show the importance of the dust storms in recent years. Moreover, spatial-temporal identification and analysis of the properties of these dust particles is very important in order to manage this crisis and prevent the harmful effects of dust particles. In Iran, due to desert conditions, the presence of dust hotspots has always caused air pollution and reduced the quality of life of people. In recent years, some dust hotspots have been ambiguous about increasing the intensity of dust emission. In this study, using the AOD product of MODIS, which compute the dust intensity, and based on the annual frequency and averages of dusty days, the location of dust hotspots were identified and then the trend of dust intensity in each hotspots were examine. The results showed that despite the relatively similar climate, the trend of changes in these dust hotspots does not follow the same pattern and complex human activities and natural changes.Data and Method In this study AOD product from MODIS with the resolution of 10 km was used to extract dust information then the frequencies of days with AOD greater than 0.6 per year were extracted. In addition to correctly calculating the average of AODs, calculating the number of days without data is also important in the results. The spatial and temporal distribution of the study period, were identified in three periods, 2000-2006, 2007-2012 and 2013-2018. The percentage of changes in each of the dust sources compared in different periods. The standard deviation was extracted to identify the areas most vulnerable to dust storms. Finally, to detect the quantitative distribution, the trend of AOD changes in the extracted dust hotspots was used to investigate the changes in the dust intensity trends.Results and DiscussionThe map of dust hotspots in the first period shows the main dust sources are in the north of Sistan and Baluchestan (Zabol) and south of Sistan and Baluchestan (Chahbahar), in the southeast of Semnan (Dasht Kavir), Damghan, Garmsar, Jazmourian, southwest of Hormozgan, (Bandar Lengeh area), south and southwest of Khuzestan, southwest of Yazd (Nayer), as well as parts of Qom, Ilam (Mehran), Isfahan, and south of Fars provinces. In the second period of study, many dust centers have become more intense and extensive. According to the map of dust centers in the third period of studies, compared to the first and second periods, the area of dust centers has decreased.According to the results, about half of the areas without emission has been turned into areas with dust with different frequencies in second period, and also about half of the area of very high-frequency hotspots has been turned into other dust sources with less intensity in the third period. Also, the most fluctuations in dust intensity have occurred in Sistan, Jazmorian, southeast of Semnan, East Azerbaijan, Zanjan and Khuzestan provinces. The results of trend analysis of dust intensity in different dust hotspots show that despite the relatively uniform climate, the dust sources trends in different dust sources do not follow the same pattern.ConclusionDue to the geographical location of Iran and the existence of vast deserts, the wethear has always affected by dust sources of inside and outside of the country. In this study, using satellite data with appropriate resolution, the location of dust sources in three time periods were extracted. The changes of each dust intensity class in the second and third periods were compared with the first period so that regardless of location, changes in dust intensity can be evaluated in general. Then, using the standard deviation method, the dust hotspots with the highest percentage of changes were identified. Finally, the trend of changes was calculated by examining the trends of changes in 24 main dust centers. According to the results of the present study, many changes have been observed in some dust sources and the intensity of dust in many dust sources has decreased. While some sources such as Isfahan, and Khuzestan province due to the role of human factors such as agricultural activities as well as the reduction of surface and ground water and as a result of drought and changes in soil texture have an increasing in trend of dust intensity. Since a decreasing trend is observed in most of dust sources, eastern and southern parts of Iran, the results of this study indicate the key role of climatic factors in changes and fluctuations in dust emission in Iran. Because climatic factor can be the only factor which has a relatively uniform effect on the dust emission on a large scale of Iran.
Climatology
Khalil Valizadeh Kamran; Soodabeh Namdari
Abstract
Introduction In recent years because of decrease of precipitation, use of water for agriculture, construction of hydraulic structures and etc, Urmia Lake surface area has been decreased. Considering the salinity of Urmia Lake and direction of wind, the costal and even further area of Urmia Lake is seriously ...
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Introduction In recent years because of decrease of precipitation, use of water for agriculture, construction of hydraulic structures and etc, Urmia Lake surface area has been decreased. Considering the salinity of Urmia Lake and direction of wind, the costal and even further area of Urmia Lake is seriously in danger of salt intrusion. Then knowledge of the spatial-temporal distribution of aerosol characteristics is critical for quantification of salt intrusion impacts. Aerosol optical depth (AOD) is a column-integrated measure of extinction coefficient, representing the attenuation of solar radiation by aerosol scattering and absorption. Satellite images of AOD are useful for studying dust storms owing to the large spatial nature of such plumes. Lack of an AERONET station makes studying dust storms difficult in this area. The present study was conducted to understand spatial AOD patterns and the variability and intensity of inter- and intra-annual MODIS AOD for the longest possible period of 14 years (2000–2015). Methodology In this study, monthly AODs from average MOD08 are used to investigate the spatial and temporal distribution of dust storms over Urmia lake for the period between 2000 and 2015. Monthly average MOD08 product files are available at spatial resolution of 1 degree by 1 degree (http://ladsweb.nascom.nasa.gov/data). This study focuses on AOD at 550 nm over land, as this is close to the peak of the solar spectrum and is, therefore, associated with major radiative effects (Papadimas et al. 2009). MODIS data are compared to AERONET data at the nearest station (Kuwait University) for the period between 2005 and 2014 (http://giovanni.gsfc.nasa.gov/aerostat/). The AERONET site shows better AOD correspondence with MODIS Terra (RMS = 0.028, R = 0.916) than with MODIS Aqua (RMS = 0.166, R = 0.646); therefore, hereafter AOD data are discussed from Terra. In this study, monthly mean aerosol optical depths (AODs) from MODIS are used to investigate the spatio-temporal distribution of aerosol in these affected areas (2000-2015). The monthly and annual mean AOD trends has been extracted. With the aim of displaying and analyzing the spatial distribution of particulate matter concentrations, the mean change map was extracted and each map was classified according to the standard deviation method. Using the standard deviation method, the amount of change in each of the pixels can be determined from the mean of the region. Results and discussion The changes in dust concentrations for shows that in June, July and April, there is the most similarity is between the trend of change in order in West Azerbaijan and East Azerbaijan. There are two provinces under study, and in February, November and December there is the most differences between the two provinces, which has declined sharply since 2009. Also, the trend of changes in all months shows that the slope of AOD changes has been increasing during the study period. Most monthly AOD fluctuations are seen in January, February and December during different years; It is worth noting that in these months, in terms of dust concentration, AOD also shows low values. The increasing trend of fine dust is much more pronounced at the end of the warm season and the beginning of the cold season (August, September, October and November). Most AOD values are observed in spring and early summer, ie in March, April, May, June and July. Until 2008, the amount of AOD in the southwestern part of the study area was high, indicating that fine dust observed in the southwestern part of the region could be carried by westerly winds from the deserts of neighboring countries during these years. From 2009 to 2014, the average amount of fine dust in Pixel of including Lake Urmieh, increased sharply over the entire region, which cannot be attributed to dust carried by western winds due to the AOD status in the west and southwest of the lake. Conclution In this study, annual and monthly averages were used to examine how dust changes in the last 16 years in the provinces of East Azerbaijan and West Azerbaijan, which are adjacent to Lake Urmia. One of the main objectives of this study was to monitor the oscillations of fine dust in the area of Lake Urmia and its adjacent areas to show the presence of salt dust in Lake Urmia, which has been the result of the drying up of large parts of the lake in recent years. The monthly and annual mean AOD trends show the increasing trend in AOD values. Then to show the spatial distribution during the period of study, mean annual maps for each year was extracted. Results show there is two seperated period in area of study for AOD spatial pattern. First during 2000 to 2009 there is higher AOD in south-western part of area and the existence of Urmia lake had caused reduction in AOD in western part of lake. Second period started from 2010 there is significant high AOD above Urmia lake. This fact shows the lake as a source of aerosols. In next step to show the spatial distribution of AOD changes during time, based on AOD value two years with high (2014) and low (2004) AOD was selected. The difference between these two years shows the most changes in area of study has occurred over Urmia lake and also around the lake. Based on the result of this study the increase of salty aerosols that originated from Urmai lake is one of major aspect of drought of the parts of lake and must be considered.
