IGCESH2016 Universiti Teknologi Malaysia, Johor Bahru, Malaysia 15 -17 August 2016 TRENDS IN ANNUAL RAINFALL MAXIMA IN SARAWAK, MALAYSIA UNDER THE HYPOTHESIS OF SCALING EFFECT Zulfaqar Sa’adi* 1 , Shamsuddin Shahid 2 , Tarmizi Ismail 3 , Morteza Mohsenipour 4 1, 2, 3 Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor Bahru, MALAYSIA (E-mail: zulfaqar19863@gmail.com, sshahid@utm.my; tarmiziismail@utm.my, mortezamohsenipour@gmail.com) ABSTRACT The natural variability is required to be removed from the rainfall time series in order to quantify the global warming which induced changes in precipitation. The Mann-Kendall (MK1) test and modified Mann-Kendall (MK2) test, which can discriminate multi-scale variability from unidirectional trends, was used to analyze the variability and spatial distibution of rainfall trends in Sarawak of Malaysia for the period of 1980–2014. Trends in six indices related to annual rainfall maxima namely, maximum 1-, 3-, 6-, 12-, 24- and 72-hour rainfall in a year were assessed. The MK1 method showed changes in 1-, 3-, 6-, 12-, 24- and 72-hour annual maximum rainfall at 7, 5, 6, 6, 5 and 6 stations respectively out of 26 stations at 90% level of confidence. On the otherhand, the MK2 method showed changes in only 3, 5, 6, 3, 3, and 3 stations respectively. This indicates that significant changes in annual maximum rainfall estimated by most of the stations using well-known Mann-Kendall method are due to scaling effect. The results also revealed that significant changes are mostly positive, which means indices related to annual rainfall maxima are increasing in some parts of Sarawak. The spatial distribution of trends revealed that the significant increase in rainfall maxima mostly in south and central parts and decrease in the north of the state. Significant changes in rainfall maxima were also noticed in the regions that receives relatively lower amount of rainfall, located in the coastal part of Sarawak which is prone to floods during the Northeast monsoon. Therefore, increasing in annual rainfall maxima indicates probability of more floods in the region in future. Key words: Unidirectional Trends; Scaling Effect, Modified Mann-Kendall Test; Annual Rainfall Maxima 1.1 INTRODUCTION The subject of rainfall trend detection in hydrologic data has received a great deal of attention lately, especially in connection with the anticipated changes in global climate. With the recent extensive work in the field of climatic change and variability, the subject of rainfall trend detection has been pursuing more extensively. Rainfall and temperature are often used as important climate parameters to determine changes in global climate. Lots of studies have been