Nafiseh Seyyed Nezhad Golkhatmi; Javad Bazrafshan; Arezo Nazi Ghameshlou; Parviz Irannejad
Abstract
North Atlantic Oscillation (NAO) is one of large-scale signal that affects the north hemisphere. Various studies have investigated the correlations between Iran’s precipitations and North Atlantic Oscillation from monthly to yearly scales. This study has considered weekly time scale. The daily ...
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North Atlantic Oscillation (NAO) is one of large-scale signal that affects the north hemisphere. Various studies have investigated the correlations between Iran’s precipitations and North Atlantic Oscillation from monthly to yearly scales. This study has considered weekly time scale. The daily precipitation variable was obtained from the ERA-Interim database (grid) and its compliance with ground reference points (synoptic) were investigated (1979-2016). The results showed that the amount of annual precipitation in regions with more humidity, especially in the Caspian region, is underestimated. Also, the correlation between grid and synoptic precipitation data in the western, northeastern and southeastern area of the country is the highest and in the strip parallel to the western-eastern line (the middle areas) is the lowest (weekly average). This correlation decreases from winter to autumn and spring, respectively. A review of the time series of the sever events of NAO during the year with the weekly scale showed that this signal had two peaks, which was used to select the time period of assessing the relationship between precipitation in Iran and NAO. The results showed that the correlation between grid precipitation and NAO is not completely direct and relative frequency of direct correlation is more than non-direct type and decreases from north to south.
Shirin Mohammadkhan
Abstract
The phenomenon of dust storm causes a number of damages such as aggravation of heart or lung disease, air and land traffic. Occurrence of dust storm has been growing inrecent years and has created many problems in some cities of Iran. Dust storms of Iran arise either from internal or external sources. ...
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The phenomenon of dust storm causes a number of damages such as aggravation of heart or lung disease, air and land traffic. Occurrence of dust storm has been growing inrecent years and has created many problems in some cities of Iran. Dust storms of Iran arise either from internal or external sources. In this paper, Climatology of dust storms in Iran is compiled based on observational data of 112 meteorological stations from 1985 to 2005. Results show that the total number of dust stormy days varies from 11 to 3833. Accordingly, we have identified five types of cities; 1- less than 492 days; 2- from 588 to 1153 days; 3- from 1243 to 1757 4 days; from 2007 to 2239 5 days; 5- more than 3832 days. Afterwards, we examined each of them separately. The first group is fixed. Cities of this group are located mostly in North, East and Center of Iran. The second group contains three parts:First, an ascending trend to 1992 and then a descending part to 1998 and again,an ascending part to 2005. Cities of second group are located in the southern pasrt of the country. The third group contains four parts: First, a down trend to 1990 and then an ascending part to 1993 and again, a descending part to 1998 and finally, a branch of the ascending to 2005. Cities of the third group are located almost in the southwest. The cities of the fourth group are located in Sistan&Baloochestan province and are affected by the120-day wind. The occurrence of dust storm in the fourth group is ascending. Finally, using GIS and interpolation systems, we have plotted dust storm zone classification map of Iran from 1998 to 2005.
محمد قبایی سوق; Abolfazl Mosaedi
Abstract
Reconnaissance Drought Index (RDI) is based on fitting a Log-normal distribution to the ratio of precipitation to evapotranspiration (ETo) values in selected periods. In this index value of ETo were calculated based on mean temperature by Thorenth-Waite (Th) method. Th method, may underestimated ETo ...
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Reconnaissance Drought Index (RDI) is based on fitting a Log-normal distribution to the ratio of precipitation to evapotranspiration (ETo) values in selected periods. In this index value of ETo were calculated based on mean temperature by Thorenth-Waite (Th) method. Th method, may underestimated ETo values comparing to the actual in arid and semi arid regions. The log-normal distribution may not be fitted to the ratio of precipitation to ETo values of some regions. In order to investigate the effects of these two limitations on drought situations' changes, meteorological parameters have been used during 50 years period at 8 Synoptic Stations of Iran. In the first step, the values of RDI(Th) for any stations during the mentioned time were calculated. Then, ETo values were calculated from best fitted empirical equation in any situation of lack of parameters. Subsequently RDI(select) index were established. The Kolmogorov–Smirnov (KS) test is used to assess the goodness of fitting most appropriate distribution function to the ratio of precipitation to ETo values. Then, according to equi-probability transformation the values of RDI(Th) were modified to *RDI(Th). The occurrence of different classes of drought according to RDI(select) and/or *RDI(Th) comparing to RDI(Th) showed the elimination of any mentioned limitations may leads to changing the amount of occurrence of any drought classes in RDI(Th). Hence, The RDI(Th) modified to *RDI(select) by estimating ETo values from selected method and applying appropriate distribution function to the ratio of precipitation to ETo values.
Maryam Azarakhshi; Jalil Farzadmehr; Mahdi Eslah; Hossein Sahabi
Abstract
Climate change is defined as long term and irreversible changes in the climatic behaviorof a region. Many studies have been conducted in different regions of the world on climatechange. The results of these studies show considerable changes in climatic factors especiallyin precipitation and temperature. ...
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Climate change is defined as long term and irreversible changes in the climatic behaviorof a region. Many studies have been conducted in different regions of the world on climatechange. The results of these studies show considerable changes in climatic factors especiallyin precipitation and temperature. In this research, the trend of changes in annual and seasonalrainfall and temperature in 24 synoptic stations over a 50-year data period (1956-2005) wasinvestigated in Iran. The Mann- Kendall test and linear regression technique were used to analyzethe trend of changes in climatic factors. The results showed both increasing and decreasingtrends in annual rainfall at various regions of Iran. Annual rainfall in northern slopes of Alborzand western slopes of the Zagros Mountain as well as in eastern and southeast parts of Iran hada decreasing trend while in the central of Iran the trend of changes was increasing. In southernregion of Iran the rainfall had an increasing trend. The results also showed that temperature inmost of the studied stations over the considered period was increasing. The highest and lowestchanges in temperature were seen in the mean temperature of summer and winter, respectively.Ahwaz and Khorramabad stations had a decreasing trend and over all seasons would go towardmore cooling. The temperature trend in Oromiye was decreasing in autumn and summer whileShahrekord and Bandar abbas had the same trend in summer and winter.
Ataolah Kavian; Fatemeh Adineh; Gorban Vahabzadeh; Abdolvahed Khaledi Darvishan
Abstract
Investigating downstream changes in bed load shape can be useful to detect watershedhydrological processes and it is very important to design hydraulic structures and to managecapacity of large storage dams, properly. Regarding to doing of enforcement studies, thisresearch was conducted in Qalesar River ...
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Investigating downstream changes in bed load shape can be useful to detect watershedhydrological processes and it is very important to design hydraulic structures and to managecapacity of large storage dams, properly. Regarding to doing of enforcement studies, thisresearch was conducted in Qalesar River in upstream of Chahardangeh watershed in MazandaranProvince. After recognition of the study area, 6 sections were selected towards downstreamfor bed load sampling. Laboratory analysis were done to measure and calculate some bedload shape characteristics including skewness, kurtosis, mean, mode, percent of sand, finegravel, silt and clay, sediment texture, small, medium and large diameters, nominal diameter,sphericity, rounding, width ratio, shape factor and D10, D50 and D90. Results indicated adecreasing trend in shape factor and sphericity, an increasing trend in mean diameters androundness, a complex trend in width ratio and a uniform trend in 3 axes. Our finding alsoindicated that this variations may be affected by physiographic, lithologic and geotechnicalcharacteristics of the study area.
