An Overview on Isotopes in Precipitation of Bangladesh

The monthly weighted mean stable isotopic composition of rainfall in eight GNIP (Global Network of Isotopes in Precipitation) stations of Bangladesh vary in a short range i.e. δ¹⁸O = −6.998‰ to −5.58‰. The weighted δp value shows the order as HT > XB > SR > CN > DN > KH > BN > BS although modification of trend occurs when considered differently for monsoon and non-monsoon periods. Pre or post-monsoonal rain shows relatively enriched signature compared to the monsoon period. The local meteoric water lines (LMWLs) are much similar to Craig’s GMWL (Global Meteoric Water Line) except DN. The way of the effects from meteorological control vary according to seasons and locations. The spatiotemporal distribution of humidity accounts for ≈34% of isotopic variation. Temperature effect is most prominent in CN (41%, non-monsoon) and BS (19%, monsoon). Around 50% dependency on precipitation amount has been observed in coastal stations and DN during January to May, while monsoon precipitation is mostly characterized by reduced amount effect and “anti-amount effect”. Moreover, wide range of d-excess during non-monsoon precipitation bears the evidence of mixture of vapour from different sources and recycling events. However, monsoonal vapour source is rather consistent since d-excess value varies within a little margin.