Fluctuations in Monthly and Annual Rainfall Trend in the Limbang River Basin, Malaysia: A Statistical Assessment to Detect the Influence of Climate Change

Fluctuations in monthly and annual rainfall trends in the Limbang River Basin, Malaysia were characterized through Cramer's (t(k)) test and linear regression (LR) methods. Rainfall measurements from four rain gauging stations having 35 years (1981-2015) of data were grouped in to 110 years non-overlapping and 15 years overlapping monthly and annual rainfall totals for the analysis. Analysis of monthly rainfall in the initial sub-periods of 10 years non-overlapping (1986-1995) indicate significantly decreasing trends in all rain gauging stations during the months January, October. December and 15 years overlapping (1981-1995 and 1986-2000) in the months of January. March, April. October, November and December. Annual rainfall trend in these sub periods also confirms the same and suggesting dry condition in the region. During the sub-periods (1996-2005 and 1996-2010), the monthly and annual rainfall trends started showing significant increasing trends indicating wet condition in LRB. This period can be considered as a transition period in general rainfall pattern in LRB because the 10 years moving average rainfall also peaked above the long-term average rainfall in all stations. Significant increasing trend in monthly rainfall in 10 years non-overlapping (2006-2015) periods is associated with January, March, November and December whereas in 15 years overlapping period (2001-2015) indicate a significant increase during the months of Januaty, March, April, November and December. Increasing rainfall trend in monthly and annual total revealed by linear regression analysis shows an overall increase of >1000 mm annual rainfall in all rain gauging stations with approximately at the rate 1% per year. However, fluctuation in annual rainfall indicate the influence of regional climatic phenomena on rainfall characteristics of LRB.