Regional distribution of intensity–duration–frequency (IDF) relationships in Sultanate of Oman

Analysis of extreme rainfall parameters including rainfall intensities is a fundamental requisite in safe planning, designing, and operating various hydrologic and water engineering projects against storms and floods. In arid and semi-arid regions, such as Oman, sufficient long-term rainfall data with short aggregation are usually not available in most locations across the country. This paper presents the development of intensity duration frequency (IDF) curves using the available rainfall data from 65 metrological stations situated at different elevations and regions throughout Oman. Gumbel distribution was fitted to the observed data and rainfall intensities were found for various return periods. Rainfall analysis showed the average annual rainfall of 109.21 mm with a standard deviation of 92.82 mm, Skewness coefficient of 1.62 and Kurtosis coefficient of 3.08 for all the studied stations from 1977 to 2017. The statistical analysis showed that the estimated rainfall intensities for various return periods are high in the mountainous region compared to the desert or interior region, and the coastal region of the country. Also, the empirical parameters of IDF formula for all studied stations were established using non-linear regression. Finally, the contour maps for all the parameters were drawn which could be used to determine the IDF relationships for ungauged locations. This study will be useful for the decision makers and practicing hydrologists for planning and design of water resources systems in Oman.