Trend Analysis of Climate Variability in Salalah, Oman

Abstract

The frequency and intensity of weather events are expected to change as climate change, which may result in more frequent and intensive disasters such as flash floods and persistent droughts. Subsequent impacts will affect regions in different ways, but projected to worsen conditions in water scares countries like Oman. In Oman, changes in precipitation and temperature have already begun to be detected, although a comprehensive analysis to determine long-term trends has yet to be conducted. We analyzed daily precipitation and temperature records in Salalah city of Oman, mainly focusing on extremes. A set of climate indices, defined in the RClimDex software package, were derived from the longest available daily series (precipitation over the period 1943-2011 and temperature over the period 1991-2011). Results showed significant changes in daily minimum and maximum temperatures associate with cooling as well as warming. The annual number of cold nights (percentage of days when daily minimum temperature (TN) less than 10th percentile of that during base period: 1991-2000) decreased by 8 days per decade (p-value = 0.3). On the other hand, the annual number of warm nights (percentage of days when daily minimum temperature (TN) larger than 90th percentile of that during base period) increased by 10 days per decade (p-value = 0.3). In contrast, the annual occurrence of cold days increased by 11 days per decade (p-value = 0.25), while the annual occurrence of warm days decreased by 4 days per decade (p-value = 0.62). The significant trends apparent in minimum temperatures reveal that Salalah area has become less cold rather than hotter. Moreover,
contrary trends in minimum and maximum temperatures indicate that, in long-term, daily temperature range has decreased in this area. Annual total precipitation averaged over the period 1943-2011 is 95 mm, which shows a statistically weak negative trend with a -2 mm/10 yr rate. There is also a tendency for precipitation extremes according to many indices. The contribution from very wet days to the annual precipitation totals steadily increases with significance at 87% level. The positive trend in simple daily intensity index is also clear and reasonably significant (p-value = 0.29). Results of all these indices lead us to conclude that precipitation intensity in Salalah has increased while mean
precipitation changes are less marked.