There are numerous lakes on the Tibetan Plateau(TP),but the role of lake temperature in precipitation over the TP remains unclear.Here the Weather Research and Forecasting(WRF) model was used to detect the impact of lakes on summer rainfall.Three test cases were used to evaluate the effect of lakes surface temperature(LSTs) on precipitation variability.The three cases used different methods to determine initial LSTs,including using sea surface temperature data(SST),the WRF inland water module(avg_tsfc),and a lake model.Results show that when precipitation was stimulated over the TP,LSTs cannot be initialized using SST,which led to large discrepancies of precipitation.Compared with the simulations,the simulated precipitation were improved obviously with LSTs using avg_tsfc,indicating that LSTs have an considerable influence on determining precipitation over the TP.Due to a lack of observational data,the lake scheme does not improve on rainfall simulation,but does effectively simulate precipitation pattern over lakes,such as rainfall over the lakes was dominated by convection during the nighttime.Though the simulated precipitation using SST to initialize LSTs caused largediscrepancies,it suggested that precipitation increase especially convective precipitation with increase in LSTs,which confirmed that the moisture from lakes cannot be neglected over the TP.Generally,it was necessary to monitor the LSTs for accurate weather and climate prediction over the TP.
Based on the glacier mass balance and meteorological data of air temperature and precipitation on the Qiyi Glacier from June 30 to September 5,2010,we used a degree-day mass balance model to simulate the change of mass balance during this period.Our results indicate that the current value of the mass balance is 856.2 mm w.e.Subjected to the strong influences of air temperature and precipitation,the mass balance process can be divided into three stages:accumulating exiguously → melting intensively → melting exiguously.The variation trends of the mass balance according to the degree-day mass balance model and the observed values are similar and wholly reflect the spatial distribution characteristics of the glacier mass balance,which increases with the increase of altitude.Our experiment on climate sensitivity of the mass balance showed that mass balance was very sensitive to the change of temperature;air temperature is the key factor which influences mass balance;and a slight increase in precipitation will have a negligible effect on mass balance when the air temperature increases continuously.
The Tibetan Plateau(TP) holds ten thousands of alpine glaciers in mid-latitude.They have shrunk with an accelerating retreat rate recently.We applied a distributed temperature-index massbalance model developed by Regine Hock,and coupled with a volume-area scaling method to Xiao Dongkemadi Glacier(XDG) in the central TP,to assess its response to climate change.The result shows the simulated mass balance is in a good agreement with observations(R^2=0.75,p<0.001) during the period of 1989-2012.The simulated mean annual mass balance(-213 mm w.e.) is close to the observation(-233 mm w.e.),indicating the model can be used to estimate the glacier variation in the future.Then the model was forced by the output of Reg CM4 under the climate scenarios RCP4.5 and RCP8.5 from 2013 to 2050.The simulated terminus elevation of the glacier will rise from 5454 m a.s.l.in 2013 to 5533 m a.s.l.(RCP4.5) and 5543 m a.s.l.(RCP8.5) in 2050.XDG will lose its volume with an increasing rate of 600-700 m3 a-1 during the period of 1989-2050,indicating the melting water will enhance the riverrunoff.But for the long term,the contribution to the river runoff will decrease for the shrinkage of glacier scale.
SHI Pei-hongDUAN Ke-qinLIU Huan-caiYANG Jun-huaZHANG XiaoSUN Jian-yong
Due to climate changes, most of the alpine glaciers have retreated dramatically during the past decades. Thus it is significant to predict the alpine glacier variability in the future for a better understanding of the impact of climate changes on water resource. In this paper, we perform the numerical simulation on Urumqi Glacier No.1 in the eastern Tianshan, central Asia (hereafter Glacier No.1 for short) by considering both the mass balance and ice flow. Given the shape of the Glacier No.1, the velocity of the glacier is obtained by solving a two-dimensional nonlinear Stokes equation and simulated result is in agreement with the observation. In order to predict the variability of Glacier No.1 in the next decades, a climatic scenario is constructed with a temperature rise rate as 0.17°C/10 a and precipitation as constant during the period of 2005-2070. The simulation shows that, the glacier terminus will retreat slowly and the glacier will thin dramatically before 2040, while after year 2040, the glacier terminus retreat will accelerate. This study confirms the increasing retreat rate of alpine glaciers under global warming.
