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[1] A detailed study of the climatic significance of d 18O in precipitation was completed on a 1500 km southwest-northeast transect of the Tibetan Plateau in central Asia. Precipitation samples were collected at four meteorological stations for up to 9 years. This study shows that the gradual impact of monsoon precipitation affects the spatial variation of d 18 O-T relationship along the transect. Strong monsoon activity in the southern Tibetan Plateau results in high precipitation rates and more depleted heavy isotopes. This depletion mechanism is described as a precipitation ''amount effect'' and results in a poor d18 O-T relationship at both seasonal and annual scales. In the middle of the Tibetan Plateau, the effects of the monsoon are diminished but continue to cause a reduced correlation of d 18 O and temperature at the annual scale. At the monthly scale, however, a significant d 18 O-T relationship does exist. To the north of the Tibetan Plateau beyond the extent of the effects of monsoon precipitation, d18 O in precipitation shows a strong temperature dependence. d18 O records from two shallow ice cores and historic air temperature data were compared to verify the modern d O in the ice core record in the monsoon regions of the southern Tibetan Plateau suggest past monsoon seasons were probably more expansive. It is still unclear, however, how changes in large-scale atmosphere circulation might influence summer monsoon precipitation on the Tibetan Plateau.

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Abstract:The glaciers on Tibetan Plateau play an important role in the catchment hydrology of this region. However, our knowledge with respect to water circulation in this remote area is scarce. In this study, the HBV light model, which adopts the degree-day model for glacial melting, was employed to simulate the total runoff, the glacier runoff and glacier mass balance (GMB) of the Dongkemadi River Basin (DRB) at the headwater of the Yangtze River on the Tibetan Plateau, China. Firstly, the daily temperature and precipitation of the DRB from 1955 to 2008 were obtained by statistical methods, based on daily meteorological data observed in the DRB (2005)(2006)(2007)(2008) and recorded by four national meteorological stations near the DRB . Secondly, we used 4-year daily air temperature, precipitation, runoff depth and monthly evaporation, which were observed in the DRB, as input to obtain a set of proper parameters. Then, the annual runoff, the glacier runoff and GMB were calculated using the HBV model driven by interpolated meteorological data. The calculated GMB fits well with the observed results. At last, using the temperature and precipitation predicted by climate models, we predicted the changes of runoff depth and GMB of the DRB in the next 40 years. Under all climate-change scenarios, annual glacier runoff shows a significant increase due to intensified ice melting.

Abstract:The mass balance of the Xiao (Lesser) Dongkemadi Glacier located in the Tanggula Mountains, of the central Qinghai-Tibetan Plateau has been monitored since 1989. The results show that the mass balance of the glacier has recently shown a deficit trend, and that the glacial terminus was also retreating. Positive mass balance of the glacier was dominant during the period 1989-1993, and the accumulated mass balance reached 970 mm. However, negative mass balance of the glacier has occurred since 1994, except for the large positive mass balance year 1997. The mass balance was 701 mm in 1998, an extremely negative glacier mass balance year. The equilibrium line altitude showed a significant increasing trend. The mass balance of the glacier has changed from a significantly positive mass balance to a strongly negative mass balance since 1994. Meteorological data suggest that the rapid decrease in the mass balance is related to summer season warming.

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The 213 m ice core from the Puruogangri Ice Field on the Tibetan Plateau facilitates the study of the regional temperature changes with its δ 18 O record of the past 100 years. Here we combine information from this core with that from the Dasuopu ice core (from the southern Tibetan Plateau), the Guliya ice core (from the northwestern Plateau) and the Dunde ice core (from the northeastern Plateau) to learn about the regional differences in temperature change across the Tibetan Plateau. The δ 18 O changes vary with region on the Plateau, the variations being especially large between South and North and between East and West. Moreover, these four ice cores present increasing δ 18 O trends, indicating warming on the Tibetan Plateau over the past 100 years. A comparative study of Northern Hemisphere (NH) temperature changes, the δ 18 O-reflected temperature changes on the Plateau, and available meteorological records show consistent trends in overall warming during the past 100 years.