Forecasting of Rainfall Using General Circulation Model-Statistical Modelling in Johor

Immaculate prediction of rainfall in a catchment is intrinsic for hydrologists to facilitate water resources management and flood risks assessment. Hence, the forecast rainfall and rainfall pattern, due to climate change needs to be investigated for guidance in managing water resources in Johor. In this paper, the impacts of climate change on rainfall variability in Johor was investigated by using General Circulation Model (GCM) on the availability of daily simulation for three representative concentration pathways (RCP) scenarios, RCP2.6, RCP4.5 and RCP8.5 for interval year of Delta 2030,Delta 2050 and Delta 2080. Daily rainfall data from eight (8) stations spreading all around Johor capturing 30 years period (1988-2017) were considered for the study. There is considerable variation of mean annual rainfall in different parts of Johor. As for example, the mean annual rainfall can be as low as 1714.9 mm at Ladang Paya Lang, Segamat station to as high as 2603.6 mm at Ladang Pekan Layang-layang, Kluang. Statistical Downscaling Model (SDSM) was used effectually to carry out predictor selection as well as future rainfall projection. The study noted that temperature (nceptemp), surface specific humidity (ncepshum) and near surface relative humidity (nceprhum) had the most significant influence in the local weather formations with R values ranged from 0.5 to 0.7. In addition, low standard error (SE) ranging from 3.82% to 11.64% was observed for all the stations considered in the study. The annual mean rainfall for RCP 2.6, 4.5 and 8.5 was predicted increase by of 17.5%, 18.1% and 18.3%, respectively as compared to historical data. Kluang was predicted to receive the highest amount of rainfall, and the lowest was in Segamat. The eastern part of Johor was expected to receive higher rainfall intensity and then disperse to the western part of Johor. It is expected that improved knowledge about predictions of future rainfall will expedite the mitigation strategies regarding climate change effect in Johor.