Investigating hydrometeorology of the Western Himalayas: Insights from stable isotopes of water and meteorological parameters

Abstract

The Himalayas govern the hydrometeorology of the entire Indian subcontinent and feed 19 major rivers on which a large population is dependent. Despite its vast socio-economic relevance, there exist knowledge gaps in the detailed understanding of Himalayan hydrometeorology. The present study attempts to understand subtle hydrometeorological processes concerning precipitation in Western Himalaya (WH), which is further complex due to several mountain ranges in addition to the Great Himalaya and varied land cover. In this backdrop, oxygen and hydrogen isotopic analyses of daily precipitation samples collected from Jammu was done. Major processes and features identified are: (1) Raindrop re-evaporation is dominant, indicated by lower δ18O – δD regression slope (6.6 ± 0.2). (2) Maximum raindrop re-evaporation occurs during Western Disturbances (WD), evident from the low d-excess (<10‰) and high δ18O (>0‰) with low rainfall. (3) Contrary to expectations, negligible moisture is derived from the Mediterranean region (MR) through WD. In contrast, maximum moisture (~97%) is derived from local terrestrial sources, estimated through backward wind trajectories and confirmed by vertical wind velocity (ω) and OLR. (4) The Arabian Sea (AS) moisture contributes more (~11%) compared to the Bay of Bengal (BOB) moisture (~8%) during the monsoon. (5) Isotopically, the most depleted precipitation during July-Aug is associated with continental recycling from the Indo-Gangetic plains and not with the BOB moisture. (6) Isotopic enrichment in precipitation towards end of monsoon is attributed to raindrop re-evaporation, lesser rainout fraction and moisture derived from enriched local sources. (7) Annually, 87% of the moisture for precipitation is derived through continental recycling, and only 13% of the moisture is derived through marine sources (11% from AS and 2% from BOB). Moisture from MR (<0.1%) is negligible.