Study of stable isotope in daily precipitation for the lower Brahmaputra region at Guwahati.

This study analysed the stable isotopic composition of daily precipitation from a monitoring station established in Guwahati located near the bank of the lower Brahmaputra region. Between September 2022 and December 2023, the precipitation samples were collected for hydrogen and oxygen stable isotope analysis. The analysis was performed following the conventional analytical procedure for laser-based, off-axis integrated cavity output spectroscopy (ICOS) in Liquid Triple Isotopic Water Analyser (L-TIWA). The preliminary study helps to define Local meteoric water line (LMWL) in the Lower Brahmaputra region. The pre-monsoon samples show regression line with slope lesser and an intercept greater than Global meteoric water line (GMWL), but the monsoon samples are showing a trend line similar to GMWL. The smaller intercept difference in the pre-monsoon and monsoon rainwater samples indicates the moisture sources of precipitation in this region originating from the Indian summer monsoon more than the western disturbances. The enrichment of heavier isotopes in precipitation of different seasons might be the result of a complex interplay between atmospheric circulation, moisture sources, elevation effects, and transport processes. Further analysis by using air mass back trajectories models and GIS tools will be able to understand and correlate the diverse origin of moisture and observed daily isotopic variability.