Stable isotopic compositions of precipitation events from Kathmandu, southern slope of the Himalayas

Abstract

Investigation of temporal variations in the stable δ18O and δD isotopes from Kathmandu’s precipitation events shows that the relatively enriched δ18O and δD values in the winter (the dry season, dominated by the westerlies) were positively correlated with temperature, indicating a temperature effect controlling the changes of δ18O and δD. However, the δ18O and δD values were depleted in the summer (the wet season, dominated by the Indian monsoon), which were negatively correlated with precipitation amount, indicating an amount effect. In addition, the comparison of stable isotopes in precipitation from Kathmandu and Mawlong (near the Bay of Bengal) shows that the overall trends of δ18O and δD values at Kathmandu generally approximate those at Mawlong. However, there remain many differences between the details of the isotopic changes at Kathmandu versus those at Mawlong. Compared with those at Mawlong, the further rainout effect and the more intense lift effect of the oceanic moisture by the high mountains resulted in the more depleted δ18O and δD values in summer precipitation at Kathmandu. A deuterium excess and the local meteoric water lines reveal that evaporation at Kathmandu exceeds that at Mawlong. The data also show that the Indian monsoon activities at Mawlong are more intense than those at Kathmandu.