Abstract
Introduction/ Methods: The current study has compared the fluctuations of atmospheric precipitable water over Iran during three periods of 1948 – 1957, 1958 – 1978, and 1979 – 2012 using upper-air reanalyzed data from NCEP/NCAR. Results: The results indicated that, in all the three periods, average distribution and coefficient of spatial variation decreased with altitude. In contrast, there was a positive relationship between coefficient of spatial variation and altitude. The results of trend analysis showed that atmospheric precipitable water of Iran calculated using the upper-air reanalyzed data by NCEP/NCAR experienced various fluctuations during the three periods of 1948 – 1957, 1958 – 1978, and 1979 – 2012. The increase of the precipitable water during the first period was not significant at the level of 95%. The increase of the precipitable water during the second period was significant at the level of 95% just in 25% of the regions. In contrast to the second period, 70% of the country’s area followed a declining trend. However, this decreasing trend was not significant at the level of 95%, either. Conclusion: The results of Alexandersson statistical method showed that the biggest shift in the average of precipitable water happened during the third period. Overall, variations in the precipitable water over Iran in the past ~60 years are not within the uncertainty of the reanalysis data and are therefore clearly discernible.
Highlights
Iran is located in an arid and semiarid geographic area, with its average annual precipitation being equal to one-third of that on the global scale [1]
The current study aimed at investigating fluctuations in atmospheric precipitable water of Iran during three periods of upper-air reanalyzed data (1948 – 1957, 1958 – 1978, and 1979 – 2012)
Since the coefficient of variation is small in this period, it can be inferred that atmospheric precipitable water of Iran in the third period has experienced less fluctuation compared to that in the other two periods
Summary
Iran is located in an arid and semiarid geographic area, with its average annual precipitation being equal to one-third of that on the global scale [1]. Variations are manifested as changes in the large-scale atmospheric and/or oceanic circulation patterns. These cause shifts in the temperature and precipitation Probability Distribution Functions (PDFs) [3]. Studying fluctuations in precipitable water is a tool for water resource management. It helps scientists gain a better understanding of humidity changes. Precipitation refers to any product of the condensation of atmospheric water vapor that falls on the ground. It consists of condensation of fine water vapors in the atmosphere. The amount of precipitable water is expressed based on the altitude of water table [4]
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