A comparison of trends in extreme rainfall using 20-year data in three major cities in Oman

Many regions in the world have recently experienced more frequent and intensive disasters such as flash floods and persistent droughts. The Sultanate of Oman is no exception to this. We analyzed twodecade long daily precipitation records in three major cities, namely, Sohar, Muscat and Salalah, mainly focusing on extremes. A set of climate indices defined in the RClimDex software package was used. Moreover, annual maximum 1-day precipitations in three study areas were analyzed using the Generalized Extreme Value (GEV) distribution function. Results showed significant changes in the precipitation regime in recent years. The annual total precipitation in Sohar and Salalah decreased, while that in Muscat shows statistically week increasing trend. However, all indices analyzed indicate enhanced extreme precipitation toward 2010 in Muscat and Salalah. As a result, the contribution from extreme events to the annual total rainfall steadily increases in both study areas. A clear conclusion could not be made based on selected indices for Sohar due to consistent drier years occurred from 1999 to 2005. Frequency analysis indicates that the annual the maximum 1-day rainfall estimated in Sohar and Muscat for 5 and 10 year return periods are approximately same (70 mm/day and 108 mm/day, respectively) but about two-fold greater than that in Salalah (29 mm/day and 60 mm/day, respectively).