Frequency distributions of areal rainfall intensity and duration in western Saudi Arabia
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ORIGINAL PAPER
Frequency distributions of areal rainfall intensity and duration in western Saudi Arabia A. S. Al-Wagdany
Received: 7 December 2014 / Accepted: 6 February 2015 # Saudi Society for Geosciences 2015
Abstract In this study, rainfall analysis is carried out to investigate the areal rainfall characteristics of three major basins in western Saudi Arabia. The drainage area of study basins ranges from 395 to 3500 km2. Records of rainfall intensity and durations were collected from nine recording rain gauge located in these basins. The mean areal rainfall depth is determined and used to compute the mean areal rainfall intensity for all the recoded rainfall events. The data were also utilized to compute frequency distributions of areal rainfall intensity and duration. Exponential distributions are fitted for the areal rainfall intensity and durations. The fitted distributions are found in a good agreement with the observed frequencies. Keywords Rainfall frequency distribution . Rainfall intensity . Rainfall duration . Arid basins . Saudi Arabia
Introduction The Western region of Saudi Arabia contains the Hijaz-Asir Scarp which is one of the distinguished topographic features of the country. It extends parallel to the western coastal plains for some 1700 km, and the elevation rises to 2990 m. The slope of the mountains is relatively steep towards the sea in the west but less steep towards the east (Al-Ahmadi and AlAhmadi 2013). The topography of the region influenced its
A. S. Al-Wagdany (*) Department of Hydrology, King Abdulaziz University, P. O. Box 80208, Jeddah 21589, Saudi Arabia e-mail: [email protected]
hydrology particularly regarding flood characteristics of the region. Western Saudi Arabia is characterized by the flash floods that became very evident in the last decade (ElHames and Al-Wagdany 2012). Although several factors contribute to the occurrence of flash flood, the most important of them are rainfall characteristics. That is why it is very important to study the rainfall characteristics of the region. Rainfall characteristics of western Saudi Arabia have been investigated by several researchers. The eastern slopes of the western mountains have lower rainfall than the western side (Abdulrazzak et al. 1995). The basins in the western and southwestern regions encompass a wide range of altitude, which is matched by a marked gradient in annual rainfall, from 30 to 100 mm on the Red Sea coastal plain to up to 450 mm at elevations in excess of 2000 m asl (Wheater et al. 2008). Rainstorm durations in the region typically range between 1 and 2 h and tend to occur in mid-late afternoon (Wheater et al. 2008). The relationship between rainfall and elevation in western and south western regions was investigated by several researchers such as Subyani et al. (2010). Understanding of temporal and spatial distribution of rainfall is potentially important for solution of many hydrologic and engineering problems. In fact, knowledge of rainfall properties and variability is essential for designing and oper
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