Characteristics Of Degree-day Factors And Ablation Simulation Of Laohugou Glacier No.12 In Qilian Mountain

The Hexi Corridor is the core area of the new silk road economic belt.Qilian mountain is one of the most developed areas of glaciers in China.As a solid water body,glacier is an important water resource to maintain the socio-economic development of Hexi corridor,and also an important guarantee for the ecological health development of Qilian mountains.Glaciers are indicators of climate change,it can be established through ablation model of the relationship between melting and climate.Therefore,it is of important scientific and practical significance to carry out the simulation study on the change of glacier ablation.According to the glacier melting,it is possible to discuss the response mechanism of glacier to climate change and the change of glacier runoff,and to evaluate the change of water resources in the basin and the region in the northwest arid region.The Laohugou Glacier No.12 was taken as the research object to evaluate the typical glacier changes in the western part of the Qilian mountains,combined with the meteorological data measured at 4200m,4550m and 5040m on the glacier from January 1 to December 31,2012 and the measured material balance data at the stakes from May 28 to September 6,2012.On this basis,it was studied the spatial-temporal variation characteristics of the No.12 glacier degree-day factor according to the definition of degree-day factor and the energy balance model.And three degree-day models were constructed to simulate and evaluate the summer glacier melting in a short time scale.The following conclusions were obtained.?1?The meteorological conditions of Laohugou Glacier No.12 are as follows.The annual temperature variation range is large,the annual difference is more than23?,the daily variation range is small relatively and the average daily range is less than 6.1?.Precipitation is concentrated in the summer,it is accounting for 63%of the annual precipitation.The amplitude of relative humidity within the year is large,and the amplitude of the three stations is 32%⁷5%,37%⁸1%,40%⁷8%,respectively.The annual average wind speed of 4,200m fluctuates around 3.0m s^-1,and the annual average wind speed at 5040m is 3.6m s^-1.The wind speed increases with the elevation gradually and the solar radiation resources are abundant.The annual average downward-wave radiation(70.3W m^-2<395.9W m^-2<447.5W m^-2)and upward-wave radiation(113.3W m^-2<241.4W m^-2<334.5W m^-2)of the three stations increase with the elevation.The annual average downward long-wave radiation(220.1W m^-2>203.1W m^-2>191.5W m^-2)and upward long-wave radiation(274.9W m^-2>257.4W m^-2>245.2W m^-2)decreases with elevation.?2?The temporal and spatial characteristics of Laohugou Glacier No.12 are as follows.From the perspective of space,the degree-day factor increases with elevation.The lowest value of the degree-day factor of glacier No.12 is 1.6mm?^-11 d^-11 in the low altitude area,the highest value is 129.5mm?^-11 d^-11 in the high altitude area,and the average value is 4.8mm?^-1d^-1.From the perspective of time,the degree-day factor value has obvious inter-month change in summer.June(9.87mm?^-11 d^-1)>July(3.27mm?^-11 d^-1)>August(2.96mm?^-11 d^-1).In addition,the diurnal variation of the day factor was obvious.The daily average variation was unimodal.It gradually increased at 7 o'clock,reached the highest value at 14 o'clock(2.42mm?^-11 d^-1),and then gradually decreased until the factor value was basically close to 0 at 21 o'clock,meanwhile the minimum value appeared at 3 o'clock in the morning(0.04mm?^-1d^-1).?3?The evaluation results of ablation simulation of degree-day model are as follows.The ablation simulation was carried out by using the single-factor degree-day model,the spatial distributed degree-day model and the spatiotemporal distributed degree-day model.The correlation coefficients between the simulated value and the measured value of the three models for summer glacier melting in 2012 were 0.66,0.53 and 0.87,respectively,and all of them passed the significance test.However,the root mean square error of single factor?268.21?and spatial distributed degree-day model?145.43?is larger than that of spatiotemporal distributed drgree-day model?30.25?.And only the Nash coefficient?0.68?of the spatiotemporal distributed degree-day model is closest to 1.It shows that the simulation precision of spatiotemporal distributed degree-day model is high and the model has reliability.Therefore,the results display that the spatiotemporal distributed degree-day model is the best for the simulation of glacier ablation on a short time scale.Spatiotemporal distributed degree-day model was used to estimate the mass balance of the eastern branch and the confluence area of Laohugou Glacier No.12 below 5000m in the summer of 2012 to obtain-793.53mm w.e..