This paper describes 2007/2008 inter-annual changes in runoff from the Zhadang Glacier located on the northern slope of Nyainqêntanglha Range,Tibet,and analyzes their causes.Precipitation increased by 17.9%in summer months of 2008 compared with the same period in 2007,drainage basin runoff decreased by 33.3%,and glacial meltwater decreased by 53.8%.Change in positive accumulated air temperature explained approximately half of the inter-annual difference in glacial meltwater using a degree-day model.This suggests that the glacier is extremely sensitive to changes in air temperature.Energy balance analysis showed that change in glacier surface albedo,considered to be caused by difference in precipitation form,resulted in the large inter-annual difference in glacial meltwater.It was shown statistically that precipitation form in the summer months of 2007 was mainly rainfall which comprised 71.5%of total precipitation,while during the same period in 2008 rainfall accounted for 30.7%,with the majority of precipitation falling as snow.Precipitation form should be considered an independent factor when analyzing glacier sensitivity to climate change or forecasting the runoff from certain glaciers.
This paper presents the stable isotope data of the snow pack and summer precipitation collected at the July 1 Glacier, Qilian Mountains in northwest China and analyses their relationships with meteorologi- cal factors. On an event scale, there is no temperature effect on the δ 18O values in the summer pre- cipitation, whereas the amount effect is shown to be clear. By tracing the moisture transport history and comparing the precipitation with its isotopic composition, it is shown that this amount effect not only reflects the change in moisture trajectory, which is related to the monsoon activities, but is also associated with the cooling degree of vapor in the cloud, the evaporation of falling raindrops and the isotopic exchange between the falling drops and the atmospheric vapor. As very little precipitation occurs in winter, the snow pack profile mainly represents the precipitation in the other three seasons. There are low precipitation δ 18O ratios in summer and high ratios in spring and autumn. The Meteoric Water Line (MLW) for the summer precipitation is δ D = 7.6 δ 18O + 13.3, which is similar to that at Delingha, located in the south rim of the Qilian Mountains. The MWL for the snow pack is δ D = 10.4 δ 18O + 41.4, showing a large slope and intercept. The deuterium excess (d) of the snow pack is positively correlated with δ 18O, indicating that both d and δ 18O decrease from spring to summer and increase from early autumn to early spring. This then results in the high slope and intercept of the MWL. Sea- sonal fluctuations of d in the snow pack indicate the change of moisture source and trajectory. During spring and autumn, the moisture originates from continental recycling or rapid evaporation over rela- tively warm water bodies like Black, Caspian and Aral Seas when the dry westerly air masses pass over them, hence very high d values in precipitation are formed. During summer, the monsoon is responsi- ble for the low d values. This indicates that the monsoon can reach the western part of the Qili
