Climate Change-induced Trends in Basin-scale Extreme Rainfall in the Johor River Basin, Malaysia

Extreme rainfall has changed considerably at the global level during the last century due to climate change. This chapter discusses the study of the spatiotemporal trends of extreme rainfall patterns in the Johor river basin (JRB) using a gridded Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) daily rainfall dataset from 1981 to 2022. Eleven indices related to rainfall recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI) were considered, consisting of the number of heavy rainfall days (R10), number of very heavy rainfall days (R20), number of days above 25 mm (R25), 95th percentile of rainfall on wet days (R95pTOT), 99th percentile of rainfall on wet days (R99pTOT), maximum 1-day rainfall amount (Rx1day), maximum 5-day rainfall amount (Rx5day), consecutive dry days (CDD), consecutive wet days (CWD), annual total wet-day rainfall (PRCPTOT), and simple daily intensity index (SDII). A modified Mann–Kendall (MMK) test at a 95% confidence level was applied to show the area that is subject to change due to the influence of climate change. The findings indicate a significant increase in extreme, long-duration, and wetter rainfall events across multiple indices: R10 (26 increasing, 1 decreasing), R20 (35 increasing), R25 (29 increasing, 4 decreasing), Rx1day (1 increasing), Rx5day (1 increasing), CWD (22 increasing, 2 decreasing), and CDD (5 increasing). The upstream area is becoming more susceptible to extreme rainfall, which presents potential benefits for water availability at the Linggiu Dam and for enhancing oil palm plantation productivity. Simultaneously, the central-downstream area faces increased vulnerability to flooding but will be beneficial for the Layang and Seluyut dams. Notably, extreme rainfall is concentrated during the peak of the Northeast Monsoon (NEM) months, from November to January.