Isotope fingerprinting of precipitation associated with western disturbances and Indian summer monsoons across the Himalayas

Abstract

Precipitation samples were collected across the Himalayas from Kashmir (western Himalaya) to Assam (eastern Himalaya) to understand the variation of the stable isotopic content (\(\updelta ^{18}\)O and \(\updelta \)D) in precipitation associated with two dominant weather systems of the region: western disturbances (WDs) and Indian summer monsoon (ISM). Large spatial and temporal variations in isotopic values were noted with \(\updelta ^{18}\)O and \(\updelta \)D values ranging from \(-30.3\) to and \(-228\) to , respectively. The d-excess values also exhibit a large range of variation from \(-30\) to . In general, heavier isotopic values are observed in most of the samples in Jammu, whereas lighter values are observed in majority of the samples in Uttarakhand. Precipitation at Jammu seems to have undergone intense evaporation while that from Uttarakhand suggest normal Rayleigh fractionation/distillation of the air mass as it moves from the source region to the precipitation site and/or orographic lifting. The d-excess of rainfall in Kashmir has a distinctly higher median value of compared to other precipitation sites with a median of . Using distinct isotopic signatures, the regions receiving precipitation from two different weather systems have been identified.