Isoscapes to address the regional precipitation trends in the equatorial region of Southeast Asia

Abstract

This research was an attempt to understand spatiotemporal characteristics of stable isotopes in precipitation samples and their regional circulation patterns in Borneo. Two locations were selected in the Limbang River Basin (LRB). Monthly rainwater samples were collected from October 2016 to September 2017. Samples were analysed for δ2H and δ18O isotopes. Local meteoric water line (LMWL) for two locations showed common source of moisture. δ2H and δ18O composition did not show effect of temperature; but, inverse correlation with amount of rainfall was noted. The d-excess values more than 12‰ during northeast monsoon showed enhanced terrestrial recycled moisture; precipitation was inferred to be from evaporative moisture source during southwest monsoon with ∼9‰–∼15‰ d-excess. Average δ2H and δ18O values from the International Atomic Energy Association/Global Network of Isotopes in Precipitation stations of adjoining countries and LRB were considered to derive the regional meteoric water line for Southeast (SE) Asia. Comparison of LWML with global meteoric water line and available datasets from IAEA/GNIP locations showed the variation in rain events, evaporation effect, and change in source of atmospheric moisture. LRB slope value showed similar values with China, Indonesia, Myanmar, Singapore, and Thailand, indicating similar meteorological trend and moisture source. Backward air mass movement trajectory indicated that predominant air mass reaching LRB were from the Indian Ocean, Pacific Ocean, and terrestrial source. Results pointed the need of detailed and site-specific collection of rainwater samples for long period to detect climate change over water resources in SE Asia.