This study performed trend analysis of extreme runoff events (high flow and seven–day low flow) of four major river basins located in Peninsular Malaysia in Southeast Asia. Trend analysis using Spearman's rank test and standard normal homogeneity test using 25 years (1982–2006) of runoff data found no statistically significant trend in extreme events of Kelantan and Pahang basins. Muda was found to have a decreasing trend in high flow which was changed to an increasing trend after a significant 'change point' in year 1992, while there was a continuous increasing trend in the low flow. Similarly, Perak was found to have decreasing trend in high flow but increasing trend in low flow. Hydrological trends detected in this study vary widely among watersheds despite the fact that they are located in the similar climatic zones. We argue that the changes in flow regime are evident even at a smaller spatial scale, and the presence of trends has significant implications on how water resources be managed.
Keywords: extreme runoff, trend analysis, Malaysian watersheds, statistical analysis, Malaysia, river basins, water resources, water management