Stable isotope (δ18O and δD) dynamics of precipitation in a high altitude Himalayan cold desert and its surroundings in Indus river basin, Ladakh

Water resources in the northwestern Himalayas are influenced by the circulation of two dominant weather systems: westerlies and southwest monsoons. The effect of climate change has significantly influenced the overall behaviour of these precipitation bearing climate systems and therefore, the meteorology of the region. To investigate the source, transportation, admixture of vapor sources and post-precipitation modification of stable water isotopic composition (delta O-18 and delta D) of precipitation in the high altitude Himalayan cold desert of Ladakh, upper Indus river basin (IRB) an observational network was established. Monthly composite (n = 110) and event wise precipitation samples (n = 32) were collected during the year 2015-16 for stable water isotopes (delta O-18 and delta D). The stable water isotopic values of the precipitation samples were lower at higher altitude and in January. The monthly delta O-18 (and SD) of precipitation showed a negative correlation with altitude (R-2 = 0.93, p = .001) and temperature (R-2 = 0.71 p = .007). However, it was perceived that the stable water isotopic value of precipitation abruptly drops at all the precipitation sites in August, without considerable variation in the ambient temperature and precipitation amount signifying the alteration in moisture source. The NCEP/NCAR reanalysis and back trajectory modeling also corroborates and suggests the modification in the moisture source and reversal of wind pattern during this period. The less d-excess and lower slope (7.4) of local meteoric waterline than the global, regional and local meteoric water lines of western Himalayan, central Himalayas and Kashmir Himalayas indicate the secondary evaporation of falling raindrops below the cloud base. Lagrangian moisture diagnostic was used to recognize the sources, which endorsed the quantitative distinction of different evaporative moisture sources.