Temporal characteristics of stable isotopes of oxygen (18O) and hydrogen (2H) at Senai, Johor, Malaysia.

The present research aimed to characterize the temporal variation in the compositions of stable isotopes ($\delta D$ and δ¹⁸O) at Senai in Johor, Malaysia. Long-term monthly data collected from Malaysian Nuclear Agency and the International Atomic Energy Agency (IAEA)/World Meteorological Organisation (WMO), Global Network for Isotopic Precipitation (GNIP) for a period of 2013-2021 were considered. The isotopic composition was evaluated monthly, seasonally and annually by taking into account the amount of precipitation (rainfall), temperature and relative humidity. The δD and δ¹⁸O values showed enriched values in the months of January, February and March and depleted values in November and December, respectively. Considering the seasonal characteristics at Senai site, it was found that the precipitation during the northeast monsoon (NEM) showed a slight enrichment in isotopic compositions as compared to the rainfall during the southwest monsoon (SWM). The primary sources of moisture were identified through the modelling of HYSPLIT-based backward trajectories, which indicated that the Pacific Ocean, the South China Sea (NEM season) and the Indian Ocean (SWM season) play significant roles as moisture contributors. Additionally, landmasses in the western Pacific and northern continental regions also supplied moisture that influenced the composition of stable isotopes in precipitation in Senai. The findings of this study contribute to a deeper comprehension of the hydrometeorological processes at play in the study area, which affect the fluctuations of compositions of stable isotopes in precipitation within the region. Further, a more comprehensive investigation of δ¹⁸O and δD isotopes is deemed crucial as essential climate response variables. This research will enhance our understanding of the hydrological cycle and improve predictions regarding the impacts of future climate change and alterations in ecosystems.