Characteristics of seasonal precipitation isotope variability in Indonesia

The few previous studies of precipitation isotopes (δ18O and δD) in Indonesia, based on low spatial resolution observation datasets, have found several types of patterns in their seasonal variabilities. This study conducted high spatial resolution rainfall sampling and investigated the temporal characteristics of precipitation isotope in Indonesia. Rainfall samples were collected weekly from 33 stations in Indonesia. Cluster analysis showed that Indonesia could be divided into four types based on the seasonal variability of the precipitation of δ18O. The majority of stations showed seasonal patterns in the variability of δ18O, characterized by high values in the dry season (July–October) as type 1. Type 2 also showed one peak of high δ18O but in the longer period (June– November) was similar to type 1 stations. A region of Northwest Indonesia, comprising North and Central Sumatra and western Borneo, was identified as type 3, having two peaks of high δ18O values in January–February and May–August. Another pattern of variability was the anti-monsoonal type, indicated by low δ18O in May–July found in east part of Indonesia. Asia-Australia monsoon regime was the main factor that controls seasonal δ18O variability. This research showed that stable isotope in precipitation could correspond to precipitation climatology in Indonesia.