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 causing 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 a gradual decrease till it became the lowest in October. The spatial decrease of δ18O and δD from southwest to northeast appeared in pre-monsoon and monsoon seasons together with eastward increase of d-excess. 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 detected at three stations in both monsoon and non-monsoon seasons. We suggested that convections over Bay of Bengal (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.

Atmospheric Research