Trend analysis of extreme precipitation indices over Karoon basin using APHRODITE girdded data

Document Type : Original Article


Associate professor, Dept. of Geography, Payame Noor University, Tehran, Iran


Interest in climate changes has significantly increased in recent decades due to the important economic and social consequences connected with extreme atmospheric occurrences. Hence, analysis of extreme precipitations and related extreme occurrences is of great importance in management of variety of sectors including agriculture, water resources, urbanization and transportation. In the recent research, Aphrodite gridded precipitation data set for the time period from 1951 to 2007 were applied in spatial resolution of 0.25 longitudes by latitude to explore possible trends in extreme precipitation over Karoon basin. The initial matrix of the data in the dimension of 20819*21000 was constructed for whole of the Middle East region in Matlab software. Then the second matrix in the dimension of 20819*100 was extracted from the first matrix that covered the studied region. The rows of this matrix represent the days and the columns show pixels. The selected indices used in this paper including Maximum 1-day precipitation (Rx1), Simple precipitation intensity index(SDII), Number of days with precipitation equal to or greater than 10, 20, and 25 mm(R10mm, R20mm and R25mm), Maximum number of consecutive dry and wet days (CDD and CWD) and Total precipitation when daily amounts are greater than 95th and 99th percentile of wet days(R95p and R99p) have been chosen from the indices recommended by Expert Team on Climate Change Detection and then the trend was evaluated using Mann-Kendall nonparametric test. The results illustrate that extreme precipitation trend is positive in the eastern, northern and central regions; while over a small part of the west and south, it was found to be negative. Indices did not follow any specific trend in the west part of Karoon. Not only has frequency of extreme precipitation increased, but also the intensity has been risen during the study period. In other words, the precipitation was concentrated in some days of the year and the high value of precipitation occurred during days with extreme and super-extreme precipitation. The greatest trend was seen in the indices of the simple daily intensity index (SDII), very wet days (0.99p), days with super heavy precipitation (R25) and days with very heavy precipitation (R20. The least upward trend was associated with the consecutive dry days index (CDD).


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