جستجوی مقالات مرتبط با کلیدواژه "تغییرپذیری دهه ای" در نشریات گروه "جغرافیا"

 The Intergovernmental Panel on Climate Change (IPCC) has reported that climate change results in anomalies, fluctuations or trends in climatic elements, such as precipitation and temperature. In this study, we aim to investigate the decadal changes in the probability of different durations of precipitation in Iran over the past four decades (1977-2016). To achieve this goal, we used the third version of the Asfazari database. We defined a rainy day as a day when the precipitation is more than the average precipitation in a given place. The Markov chain method was employed to estimate the probability of precipitation duration from 1971 through 2016.

We adopted the daily data of 2188 stations under the supervision of Iran’s Meteorological Organization for the period 1971 through 2016. Accordingly, we estimated the probability of precipitation duration for 1-7 days for the entire period. We investigated the decadal changes in the probability of precipitation duration for the four study decades and compared them to the whole period under investigation. To understand the spatial features of these changes, we estimated the relationship between changes in the probability of precipitation duration for 1-7 days and spatial factors using multivariate regression models.

Our findings revealed that as the duration of rainy days increased, the area affected by precipitation decreased. Therefore, the spatial distribution of the probability of precipitation duration for more than 7 days indicated the smallest area that received precipitation. The probability duration of precipitation lasting 4 days or more throughout Iran was very small, which can be attributed to the effects of local features on precipitation formation. The probability of 1-day precipitation for most regions of Iran was higher than other durations; however, there was only a probability of 1-day precipitation in half of Iran. The highest probability of precipitation duration occurred in the Caspian region, the only region that experienced all durations of precipitation, indicating the presence of various precipitation mechanisms in this area. The greatest probability of decadal changes was observed in the 1-7 day duration in the northern part of Iran, including the northwest to the east of the Caspian Sea and in the south of Alborz Mountain range. Additionally, the most changes in the probability durations of 1-7 days of precipitation in the south have been seen in Sistan and Baluchistan. The lowest probability of decadal changes was shown in large areas of the regions from the east, southeast, and southwest. Therefore, the changes in precipitation durations in the southern half of the regions were generally low; however, in the northern half, the changes were relatively significant.In general, during the four study decades, the relationship between changes in the probability of 1-7 day precipitation durations and spatial factors, particularly latitude, was positive. Thus, decreasing latitudes resulted in an increasing probability of 1-7 day precipitation.

The most likely changes in precipitation duration were related to the western and eastern coast of the Caspian Sea and the northwestern region of Iran, as well as southern Alborz, where the probability of changes decreased. The least amount of possible changes was related to the south of Iran, where only two provinces, Sistan and Baluchistan, and Hormozgan, experienced the greatest change in the probability of one to seven days of precipitation. Thus, the possible changes in the spatial continuation of precipitation in the southern half of the country were primarily low. However, in the northern half, the possible changes in the duration of precipitation were more significant. changes in the duration of precipitation, along with changes in the intensity and frequency of precipitation, can have significant consequences in extreme events such as droughts and floods. Accurately depicting changes in precipitation duration can be helpful in addressing problems concerning precipitation.

According to previous investigation and examining climatic elements, the hypotheses of global warming and consequently, global climate change is confirmed by majority of climatologists society around the world. The global changes probably continue for the next decades. The changes in climatic elements, by and large, categorized into two types; trends and variation. The trends refer to long term changes, whiles variations indicate vary time interval changes including oscillation, phase, jump (sift), and persistence.Precipitation is one of climatic elements which can properly reflect chaotic behavior of climate system, and illustrate the nature of changes in the system. Trends, Oscillation, and persistence in this element are investigated in national and international scale, whilst the decadal variations as an index of climate variation can contribute to the current literature. In current study we attempted to illustrate an objective feature of precipitation characteristics and its anomalies over four recent decades by using Asfezari National Dataset (AND).          

In the present study, the gridded precipitation data of the third version of AND with spatial resolution of 10×10 km during the time period of 1970/3/21 to 2016/3/19 (46 years including 16801 days) is used. This dataset adopted from 2188 synoptic, climatology, and rain gauge stations and subjected to interpolation by using Kriging interpolation method. The dataset covers an area from  N  and E. Accordingly, a pixels cover the area for 16203 days. Consequently, the dataset includes  dimensions.General spatial features of Iran precipitation for the whole under investigation period was studied based on climatological annual precipitation. Next, the same characteristics calculated for four decades ending up to 2016/3/19. Finally, for every decade the anomalies of precipitation in compare with the whole understudy period and its previous decades calculated in order to discover the spatial pattern of decadal fluctuation in precipitation.   

General characteristics of annual precipitation Annual mean of precipitation over Iran is 250.5 mm. Due to decline in temperature contrast and strength of fronts in the Mediterranean cyclones, as a main source of precipitation in Iran, the annual precipitation over Iran decreases from west to east, and from north to south.The annual precipitation in 63.2% of Iran is lower than the climatic annual mean. The annual mean of precipitation in this area which generally located in east and south of the country is approximately 150.5 mm. Thus, the total precipitation in this area is equal to the total precipitation in the rest 36.8% of the country which its annual precipitation is more than the annual precipitation in the country, 422 mm.  The spatial variation of precipitation is confirm by other statistics, for instance, skewness, kurtosis, the extreme threshold indices. For instance, a large part of Iran (26.73%) includes 100-150 mm annual precipitation, whiles the precipitation in 15.8% of the country reaches to 150-200 mm. Parts of northeast of Iran, and the coast  of Persian Gulf  and Oman Sea in the south, in addition to southern slops of Alborz mountain chain experience a precipitation amount of lower than 100 mm. In contrast to the above-mentioned dry regions, the (approximately) wet regions include limited areas for each precipitation class. For example, only 9.1% of the country characterized with 500 mm of precipitation, while the classes of 200-300, 300-400, and 400-500 comprise 20.62, 12.64, and 6.11 percents of the country, respectively.

Decadal variation of precipitation :

 In current section the spatial distribution and statistical features of precipitation in each decades was illustrated. The following list includes our finding of statistical - graphical analysis of precipitation in four successive decades:1)Thedifference between spatial mean and median of annual precipitation increased from the first to the last decades. The increasing in this characteristic refers to increase in spatial asymmetrical distribution of precipitation over the country.2) A comparison between spatial distribution of precipitation maps showed that generally, the areas experienced precipitation above the decadal and whole period average are decreased from the first and last decades.3) The increase in spatial skewness from the first decade to the last decade is another evidence of increasing in precipitation spatial differences.4) The last but not the least finding is the changes in the extreme threshold indices. From the first to the last decade, the range of 10th and 90th percentiles have increased.           

Previous studies depicted that the amount of Iran precipitation has decreased over recent decades. In order to investigate the role of each decade in the decreasing values, the gridded precipitation data of the third version of AND with spatial resolution of 10×10 km during the time period of 1970/3/21 to 2016/3/19 (16801 days) is used. General spatial features of Iran precipitation for the whole under investigation period was investigated based on climatological annual precipitation. Next, the same characteristics calculated for four decades ending up to 2016/3/19. Finally, anomalies of precipitation in compare with the whole understudy period and previous decades calculated in order to discover the spatial pattern of decadal fluctuation in precipitation. Our finding showed that by and large, precipitation has decreased over recent decades. The changes has been more pronounced in southern and northern coastal area, western slopes of Zagros mountain chain, and northern slopes of Alborz mountain chains. Previous researchers attribute these changes to changes in humidity advections in recent years.

A Discrimination of Roles of Internal and External Factors on the Decadal Variation of Annual Precipitation in Iran over Recent Four Decades (1975-2016)IntroductionAccording to Intergovernmental Panel on Climate Change (IPCC) the Earth's climate has been changed during recent century (IPCC, 2007). These changes may continues for the next century. The changes have happened in two ways, log- term change (trend) and variation (in form of Oscillations, phases, shifts, and persistence) (Asakereh,2017). Moreover, some of these changes are due to internal factors of a region, whilst some of them result from external culprits of a given region. The distinguish between these two groups of factors is an important scientific effort to understand the changes mechanisms governing them. The emerge of climate changes and climate variation can be traced by investigation of some sensitive climate elements. One of those chaotic elements is precipitation which experiences changes in different tempo-spatial scales (Goudi, 1994). Most of these changes, specially the trends, are studied in global (Todorov, 1985; Vining and Griffiths, 1985; Diaz et al. 1989) and national (Askari and Rahimzadeh, 2003; Asakereh,2004; Zahedi et al., 2007; Katiraie , 2007; Mohamadi, 2012; Ekhtesasi et al. 2015; Nazeri Tahrudi, 2016) scals. In the climatology literature (Singh et al. 1995; Ghayur and Masoodian, 1996; Glazirin, 1997; Mojarrad and Moradifar, 2003; Asakereh, 2004; Raziei and Azizi, 2009; Asakereh and Seifipour, 2013) spatial changes of precipitation was attributed to spatial coordination (longitude and latitude) and topographic features (elevation, slope magnitude and aspect). The temporal changes in precipitation in association with these topo-spatial factors has not been considered in details and in proper ways in climate researches. In current study we put the spotlight on the decadal variation in relation with the topo-spatial features as a representative of climate change and as a vital context of research. Accordingly, a regression model is adopted so as quantify the effects of topo - spatial factors effecting variability of precipitation over recent four decades.Materials and methodsIn order to achieve the aim of current study, two dataset were adopted; a national precipitation dataset, Esfezari, and Digital Elevation Model (DEM):The third version of Esfezari dataset is result from Kriging interpolation of daily record of 2188 synoptic, climatologic, and rain gauge stations for 46 years (1970-2016) with 10 km resolution. The 16801 daily maps with 167×205 pixels were created accordingly. Consequently, the dataset include dimensions of 167×205×16801. The DEM data with 10 meters spatial resolution was adopted from The U.S. Geological Survey which was provided by "Astet" satellite images. This dataset was applied to extract the topographic features (elevation, slope and its aspect) for Iran. To start with, the annual precipitation for the entire under investigation period (1970-2016) was analyzed according to abovementioned data. In the second place, the topo-spatial distribution of precipitation for four decades ended up to 2007-2016 was compared in an analyzing effort by using linear and non-linear correlation. In this stage, according to Law of Parsimony, it is revealed that linear correlation illustrate the relation between precipitation and topo - spatial factors in proper way. Moreover, A multivariate linear regression fitted on the five topo-spatial elements for every under study decade so as to detect precipitation accordingly. The regression model can be expressed as follow: where refers to annual precipitation in th pixel which is detected by the topo - spatial factors and considered the internal- cause precipitation. and are latitude and longitude, respectively. In the above regression model, , and are elevation, slop, and aspect of slop, respectively. Consequently, the external - cause precipitation is the model residual. Finally, the descriptive characteristics of precipitation maps of internal-cause and external - cause were analyzed. Results and discussionGeneral Features of Iran PrecipitationThe general feature of precipitation over Iran shows a decreasing trends from west to east and from north to south. The coast of Caspian Sea and the summits of Zagros Mountain chain receive the highest values of precipitation. The spatial average of annual precipitation is about 250.5 mm. The strongest relationship between precipitation and topo-spatial factors is related to longitude in negative way. This feature is reflected in eastward decreasing of precipitation. The determine coefficients for latitude and elevation are 13% and 4.5%, respectively.The variation of effects of internal and external factors In spite of the stability of the determine coefficients of all regression models for all decades, some of topo - spatial factors have noticeable variation. This feature refers to the fact that increasing in the effect of one factor may decrease the effect of other one(s). The models, however, illustrate a stable feature for precipitation over all four under study area during four decades. Consequently, the external factors are the main culprits in decadal changes of annual precipitation. Our finding showed that in the first decade the ratio of factors was 52.38% which increased gradually to 54.08% , 58.44%, and 59.72% among of four under the rest decades (Table 1). This refer to the fact that the changes in variation of precipitation is in association of global changes.Table 1: The areas under the effects of variation due to internal and external factors (%)Priod The percent of the country due to ---effects internal externalFirst decade 47.62 52.38Second decade 45.92 54.08Third decade 41.56 58.44Forth decade 40.28 59.72Entire period 44.38 55.62ConclusionThe climate and precipitation climatology of Iran is effected by internal and external factors, due to geographic features of the country. The internal factors include spatial (latitude and longitude), and topographic (elevation, slop and its aspect) features. In current study, in order to discriminate internal and external characteristics which effects precipitation variation we fitted a multivariate linear regression on internal factors to separate them out and distinct external factors. Accordingly, our finding revealed that the ratio of external factors in variability of precipitation increased from the first decade (52.38%) to the last decade (59.72%). This result is in line with previous studies (Khodadi et al. 2013; Farajzadeh and Ahmadian, 2014; Darand, 2015; Karimi et al., 2018). The most influenced area from the variations of external factors are internal parts rather than marginal parts of the country.