Climatology
Hossein asakereh; Seyed Abolfazl Masoodian; Fatemeh Tarkarani
Abstract
Introduction
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 ...
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Introduction
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).
Data and Methods
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.
Discussion
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) The difference 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.
Conclusion
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.
GIS&RS
fakhry sadat fateminiya; behrouz sobhani; Seyed Abolfazl Masoodian
Volume 23, Issue 69 , December 2019, , Pages 213-231
Abstract
Satellite images as new tools, provide new dimensions for land monitoring. In this study, in order to determine the homogeneous geographical areas in terms of leaf area, the remote sensing images of the Terra-Aqua Modis during the period of 2002-2016 with a spatial resolution of one kilometer and 8 days’ ...
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Satellite images as new tools, provide new dimensions for land monitoring. In this study, in order to determine the homogeneous geographical areas in terms of leaf area, the remote sensing images of the Terra-Aqua Modis during the period of 2002-2016 with a spatial resolution of one kilometer and 8 days’ time interval used.Leaf area was Zoning and analysis using the Matlab software and the Google Earth database. For this purpose, first, the mosaic and determination of the territory of Iran in the satellite data set of the Modis was determined. Then, a database in the field of cluster analysis, choropleth zoning created. Long-term mean temperature and precipitation data were also used in order to better understand the range of the leaf area. According to this analysis, 39.9 percent of Iran's vast vegetation is governed. The four zones identified in the country are the large, massive, moderate, and narrow areas. These four domains are respectively 0.89, 0.001, 3.31, and 35.76 of the land. The results showed that in all studied areas, the leaf area had a higher percentage during The warm period of the year due to the high temperature in this period and the presence of precipitation in the early cold season. The northern slopes of the Alborz, Hyrcanian forests, Golestan forests, Arasbaran forests are areas where there are different regions in all zones. In addition to forests, the areas identified for each generally include fields.
Geomorphology
seid hedayat allah nuri; efat fathi; seid abolfazl masudian
Abstract
Abstract Qanat is one of the most complicated human invention techniques to extract underground water in arid and semi-arid areas which has been constructed for irrigating. In spite of the Zayandehrood River’s water, Qanat in Lenjan is still an important source of water for irrigating agricultural ...
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Abstract Qanat is one of the most complicated human invention techniques to extract underground water in arid and semi-arid areas which has been constructed for irrigating. In spite of the Zayandehrood River’s water, Qanat in Lenjan is still an important source of water for irrigating agricultural areas. The “descriptive-analytic” method has been used in this research, and all data have been collected from related libraries and institutes. In this research, the relation between the qanat water quantity and the agricultural area under cultivation has been studied in Lenjan. For doing so, the statistical data has been analyzed using SPSS and Excel by standardized score analysis method. Next, the linear regression of time series, hydrograph charts, and correlation methods have been applied for further data interpretation and analysis. It has been found that the rate of qanat discharge has been decreased in Lenjan compared to the previous time periods especially in drought years. This has caused to complete dryness of some of the qanat sources during 19991-2012. In addition, a direct relation has been found between the amount of qanat water drainage and the cultivated areas which have been shown by significant factor 0.001 and the correlation coefficient 0.69.
Climatology
Peyman Mahmoudi; Mahmood Khosravi; Seyed Abolfazl Masoodian; Bahlol Alijani
Volume 19, Issue 54 , February 2016, , Pages 303-327
Abstract
To identify and detect the frequency variation trend of Iran’s pervasive and semi-pervasive frost days in the current research, minimal daily temperature data of 663 Iranian climatology and synoptic stations were acquired from Iran Meteorology Organization during the time interval between 1962 ...
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To identify and detect the frequency variation trend of Iran’s pervasive and semi-pervasive frost days in the current research, minimal daily temperature data of 663 Iranian climatology and synoptic stations were acquired from Iran Meteorology Organization during the time interval between 1962 and 2004 for October to April months. Following data acquisition, Iran’s isothermal maps for each day starting from 1.1.1962 until 31.12.2004 (9116 days) were prepared using Kirging interpolation technique in order to construct the database of the county’s minimal temperature. In the next step, frosts were classified in three types based on a spatial principle: pervasive frosts (simultaneous occurrence in more than 65% of Iran’s surface area), semi-pervasive frosts (simultaneous occurrence in 25% - 65% of Iran’s surface area), and local frosts (simultaneous occurrence in less than 25% of Iran’s surface area). Then, frequency of pervasive and semi-pervasive frost days were analyzed in three scales including monthly, seasonal, and yearly using two estimation techniques of slope SENSE and linear regression.
Results indicated that frequency of pervasive frosts in Iran held a statistically significant decreasing trend in December and January months, during winter, and also, in annual basis. But, for semi-pervasive frost days, it was observed that variation was significant only in January having a positive trend. It signifies that number of days with semi-pervasive frost increased during the 43 years under study. Therefore, number of semi-pervasive frost occurrences increased while number of pervasive frost occurrences decreased in January. The same rule holds for other scales i.e. monthly, seasonal, and yearly basis.
