Potential changes in the number of wet days and its effect on future intense and annual precipitation in northern Oman Luminda Niroshana Gunawardhana, Ghazi A. Al-Rawas, Andy Y. Kwarteng, Malik Al-Wardy and Yassine Charabi ABSTRACT The changes in the number of wet days (NWD) in Oman projected by climate models was analyzed, focusing mostly on variation of precipitation intensity and its effect on total annual precipitation (PTOT) in the future. The daily precipitation records of 49 gage stations were divided into five regions. Of the five general circulation models studied, two of them were selected based on their performance to simulate local-scale precipitation characteristics. All regions studied, except the interior desert region of the country, could experience fewer wet days in the future, with the most significant decreases estimated in southern Oman. The contribution from the cold frontal troughs to the PTOT in the northeast coastal region would decrease from 85% in the 1985–2004 period to 79% during the 2040–2059 period and further decrease to 77% during the 2080–2099 period. In contrast, results depict enhanced tropical cyclone activities in the northeast coastal region during the post- monsoon period. Despite the decreases in the NWD, PTOT in all regions would increase by 6–29% and 35–67% during the 2040–2059 and 2080–2099 periods, respectively. These results, therefore, show that increases in precipitation intensity dominate the changes in PTOT. Luminda Niroshana Gunawardhana (corresponding author) Ghazi A. Al-Rawas Civil and Architectural Engineering Department, College of Engineering, Sultan Qaboos University, P.O. Box 50 Al-Khod, Muscat 123, Sultanate of Oman E-mail: luminda@squ.edu.om Andy Y. Kwarteng Remote Sensing and GIS Center, Sultan Qaboos University, Muscat, Oman Malik Al-Wardy Soils, Water & Agricultural Engineering Department, College of Agricultural and Marine Sciences, Sultan Qaboos University, Muscat, Oman Yassine Charabi Department of Geography, College of Arts and Social Sciences, Sultan Qaboos University, Muscat, Oman Key words | cold frontal troughs, CMIP5, orographic precipitation, tropical cyclone INTRODUCTION Precipitation regimes across a range of space-time scales have changed in many parts of the world. These variations at inter-annual and decadal scales have been detected in Asia (Naidu et al. ), America (Coopersmith et al. ), Europe (Haren et al. ), and the Arabian Peninsula (AlSarmi & Washington ). Increasing frequency of these climatic anomalies might have positive or disastrous consequences, especially for the countries suffering from water scarcity. Miguel et al.() indicated that growth in gross domestic product in sub-Saharan African countries due to positive rainfall variations during the 1981–1999 period decreased the likelihood of civil war. The increase or decrease in total precipitation is generally attributed to the changes in the number of wet days (NWD) and the pro- portion of total precipitation occurring during the wet days. A decrease in the NWD, which may result in prolonged periods of drought, is considered one of the major disasters in the Arab region (Swaireh ). The Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC) con- cluded that the rise in the mean global surface air temperature by the end of the 21st century, relative to the pre-industrial period, is likely to be between 1.5 W C and 4.5 W C (Symon ). Global warming amplifies the water-holding 237 © IWA Publishing 2018 Hydrology Research | 49.1 | 2018 doi: 10.2166/nh.2017.188 Downloaded from https://iwaponline.com/hr/article-pdf/49/1/237/197307/nh0490237.pdf by guest on 13 June 2020