Spatial and Temporal analysis of rainfall in Terengganu integrated with floodplain analysis using HEC-RAS model

Recent shift in rainfall patterns in Peninsular Malaysia, characterized by increased variability and intensity, have necessitated detailed spatial-temporal analyses. These changes, affecting hydrological extremes and traditional monsoonal cycles, have been highlighted by the Malaysian Meteorological Department This study addresses existing gaps by examining recent trends and their impact on floodplains. It aims to analyze twenty years of rainfall data in Terengganu and assess floodplain impacts in its most affected districts. The methodology integrates climate change models with hydraulic modeling, employing the Mann-Kendall test and Sen’s Slope for temporal analysis in trend detection, ArcGIS for spatial analysis using inverse distance weighting (IDW), and HEC-RAS for flood inundation analysis. The results revealed significant variability in daily, monthly, and annual rainfall, with some stations experiencing more pronounced changes. Monthly and annual data indicated an overall increase in the Hulu Terengganu district. The spatial analysis showed the rainfall distribution variability, particularly in Hulu Terengganu and Kemaman districts. Floodplain analysis in Hulu Terengganu, based on the 2014 flood scenario, highlighted substantial flood inundation in Kuala Berang, with depths exceeding limits. The performance of IDW was compared with Ordinary Kriging (OK) using statistical techniques such as RMSE, MAE, and R². Although IDW proved effective, OK demonstrated slightly higher accuracy in capturing rainfall distribution. This study provides crucial insights into rainfall trends and floodplain management, which are essential for mitigating flood risks in Terengganu.