Long range transport and local source(s) of moisture associated with precipitation in the western Himalaya (WH)

Abstract

Western Disturbances (WDs) and the Indian Summer Monsoon (ISM) are the two principal weather systems driving the climate of the Hindu Kush Himalaya. WDs are dominant in the western Himalaya (WH) and ISM is dominant in the eastern Himalaya (EH). The Bay of Bengal (BoB) and the Arabian Sea (AS) are considered as the dominant sources of moisture for ISM. However, the source(s) of moisture associated with WDs is still debatable and unclear. We used precipitation isotopes and HYSPLIT modelling to understand the spatio-temporal patterns of precipitation isotopes and to estimate the contribution of various moisture sources to precipitation in the Upper Jhelum Basin (UJB), western Himalaya. The event based precipitation isotope data suggest that temperature and reversal of moisture source are the dominant climatological factors, and altitude as the dominant physiographic factor modifying the isotopic composition of precipitation in the region. Although there are many but discrete moisture sources associated with the precipitation brought by WDs and ISM including long range transport and local recycled moisture, the Arabian Sea provides a significant contribution for both systems. Monthly negative vertical wind velocity and less Outgoing Long Radiation (>240 W/m²) indicated significant convection processes throughout the year. HYSPLIT modelling and Isotope-enabled Bayesian results suggested that the long range transportation of advected moisture is dominant (53 ± 11 %) and increases with increase in altitude. The contribution from transpiration is 29 % (±7). It was also observed that out of local moisture, transpiration contributes significantly to lower altitude precipitation stations (<2000 m, asl) in summer. The study highlighted the significance of various moisture sources in shaping the hydrological regimes of the western Himalaya and highlights the role of environmental tracers to assess the hydrodynamics of the region.