The Simulation Of Glacial Runoff At The Headwater Of The ürümqi River

The glacier melt water runoff is very precious freshwater resources to dry inlandriver basin，the different time scales in the fluctuation in snow and ice melt water willoccur in the rivers of water mainly supplied abundant is change. Ice water resources onthe earth is an important part of water resources，accounts for about4/5of the freshwater resources，11%of the earth’s land covered with glacial，although most of theworld’s glaciers distributed in remote areas，but the resources of the glaciers form，leadto disaster and it’s structure of environment and instructions of climate changeinformation aroused people’s great attention. With the impact of global warming，in thewest of China appear generally back and shrinking glacier，which will course toinfluence to western ecological environment. Global warming is already known to allof us，the temperature and precipitation are the most direct elements in many climatechange factors to environment and human beings. China’s western glacier melt waterrunoff and the impact and mechanism research of runoff has become to one of the hotfields to today’s water science in the background of climate warming. Hydrologicalmodel to cold area has important meaning for us to understanding of the hydrologicalprocess. Glacial runoff of the produce confluence and mechanism of runoff is the coreof the glacier hydrological simulation research problem. Considering the research areabelongs to the typical cold regions，ice and snow and rainfall runoff belong to mixrecharge type，and ice and snow melt water account for a large proportion，so the modelmust have the simulation ability to simulate cold hydrologic process，especially for thesimulation of the glacier melt water and have the function to classification of rain andsnow， and had inspected in other cold regions. In the existing hydrologic model， thecalculation physical mechanism of melting ice and snow were unclear if use theablation coefficient method and meteorological elements regression model. Energy balance method has the clear physical mechanism，but demands higher observationdata，in the mountain area，the data is hard to meet the requirements of the model.Therefore this paper using degree-day-factor method which has certain physical basisand low requirements of input data to calculate glacier runoff，combined with HBVmodel to simulate the glacier melt water runoff of Urumqi river basin. On base of30mresolution digital elevation model (DEM) vector map of modern glaciers from theChinese Glacier Inventory， use the national meteorological offices and stationstemperature and precipitation data as the drive data to simulate the glacier runoff. TheHBV model was applied to simulate the runoff yield of the Glacier at the Headwaterof Urumqi River，while the degree-day model was used to calculate ice and snow melt.Using the hydro-meteorological and five glacier area topographic maps as themodel input，simulate the daily glacier runoff of the watershed from1980to2006，detained the soil evaporation；Based on the water balance principle，obtained theglaciers material balance and glaciers volume change sequence，and contrast thesimulation result. Through the experiment research，we have the following conclusion:1. In order to study the effect of the simulation result while the different heightdivision of the interval， this study were used respectively to100m and200m atintervals of the glacier area and the glacier is divided into eight and four highly belt，each height according to rainfall and temperature gradient with vertical decline rateinterpolation with rainfall and temperature. Contrast the simulation results，it found thattwo divisions have the same efficiency coefficient Reff with0.52， Correlationcoefficient R2in100m points for0.70with slightly higher than the200m points withthe0.69； The relative error RE basically the same also. This shows that height dividedintervals is not more smaller more accurate，in certain circumstances，rougher divisionto altitude also can get the same good simulation effect，the impact is not big to thesimulation result.2. Glacier area change will certainly produce certain effect on glacier runoff， pastresearch often take glacier area as a constant，use the fixed glacier area simulate runoff，this will produce a certain error，causing the runoff simulation too larger than the actual.After adjusting the area，the simulation has improved，use the1980area simulate therunoff of2006and consider glacier area change use the2006area simulate the runoff of2006，contrast shows that the latter simulation evidently decreased，decrease quantityachieved15%of the cumulative runoff deep.1980-2006，the runoff according to the1980area7%higher than the actual. This shows that in a long time scale，glacier areachange’s influence of the glacier melt water simulation in the model can’t be neglected. In a long time scales simulation study，can be considered the glacier area as a variableupdate year by year to improve the simulation accuracy.3.The simulation results of glacier volume change shows that: from1980to2006，the glacier volume reducing in fluctuation， total reduced2.1x107cubic meters，reflects the relatively strong material losses of river basin. Between1980and2006，ifnot consider area change，average about3%of the cumulative volume change wereovervalued. Due to the change of the glacier area，long glacier material balance (mm)can’t really reflect the glacier volume change，we suggest that use accumulated glaciervolume change in long-term glacier change may be more precise.4.Glacial runoff simulation directly affect the accuracy of river basin waterbalance and hydrological process，use degree-day factor method combining with theHBV model，he simulation accuracy study found that: The simulation accuracy of No.1glacier runoff is higher than the total control section of the glacier， there are certainspatio-temporal difference. From the space，the higher glacier area coverage，the highersimulation accuracy of the glacier melt，because No.1glacier accounts for51%of thetotal area of the study area，while the total control section glacier area accounts forabout19.4%of the total area，therefore，the accuracy of the simulation produced certaindifferences， the simulation precision greatly influences the precision of runoffsimulation. From the time，the basin of the glacier degree-day factor change with thetime scale. The interanual variability of degree-day factor will influence the glacierrunoff simulation result，use the same degree-day factor just can represent one basin ingeneral. And according to the measured material balance get annual degree-day factorto simulation runoff，which can effectively increase the accuracy of the simulation，therefore，to improve the simulation accuracy of degree-day-factor，further researchabout the degree-day factor change is necessary in the future.5. The simulation model is not consider the landform and hydrogeologicalcondition differences about the study area，for the increase of glacier melt water runoff，there are also inevitably some interference of human factors. These problems tell us ifwe want simulate accuracy reproduce the glacier melt water runoff，we need moreaccurate physical model. The soil module is the core part of the model，and the modelitself is just a simplify reproduced of a complex things. In the process of generalized，inevitably will ignore some objective factors，such as glacier area of geological andgeomorphic conditions of the macro control function and microscopic to iceevaporation and the accuracy of the soil water content.