Controls on spatiotemporal variations of stable isotopes in precipitation across Bangladesh

Indian summer monsoon (ISM), driven moisture from the Indian Ocean, is important for moisture transport to the Asian Water Towers and causing of floods and droughts in Bangladesh. Stable isotopic compositions of precipitation (δ¹⁸O and δD) are crucial tracers of ISM moisture transport processes. Here we presented spatiotemporal variations of stable isotopes in precipitation at three stations over Bangladesh in 2017–2018 to evaluate the influence of ISM on intra-seasonal variations of stable isotopes in precipitation in the south of Himalaya, combined with local meteorological data, ERA5 reanalysis and HYSPLIT model. We found that precipitation δ¹⁸O displayed the highest values in May following gradual decrease till the lowest in October. The spatial decrease of δ¹⁸O and δD from southwest to northeast was appeared in pre-monsoon and monsoon seasons together with increasing of d-excess eastwards. The weak temperature effect and amount effect were detected at Satkhira only at the daily scale in specific seasons, and the significantly negative correlations between relative humidity and δ¹⁸O were almost detected at three stations in both monsoon and non-monsoon seasons. We suggested that convections over BOB and tropical Indian Ocean and variable contributions of moisture sources are important factors controlling distinct variations of precipitation δ¹⁸O from west to east Bangladesh. Our results provided a better understanding of the ISM influence on precipitation stable isotopes and variations of the ISM moisture sources, which is crucial to address hydroclimatic interpretations relevant with ISM.