|Place of Conferral||北京|
|Keyword||藏东南 岗日嘎布山脉 气象特征 水文过程 冰川变化 物质平衡|
在全球变暖的大背景下，青藏高原冰川正在经历急剧退缩。藏东南是我国两大冰川发育中心之一，是除横断山之外海洋性冰川最重要和最集中发育的地区。本区冰川发育在西南季风进入青藏高原的重要水汽通道之上。研究本区冰川变化为了解海洋性冰川与西南季风的关系提供了一种途径。同时，冰川变化与本区水资源开发利用及与相关的地质灾害息息相关，对于本区的可持续发展起着相当大的影响。从2006年起，选取藏东南岗日嘎布地区然乌湖上游作为重点研究区进行高山气象、冰川变化及冰川径流观测，以期了解本区海洋性冰川在全球变暖背景下的生存状态，了解本区气候-冰川-径流变化之间耦合关系，为预测未来气候变化趋势及冰川灾害预警机制的建立奠定基础。本文根据所取得资料，对然乌湖地区冰川变化及其水热发育条件、冰川径流及对气候变化的响应方面进行了分析研究。论文主要内容包括以下三个方面。（1） 冰川区水热条件分析根据架设在冰川区的两台自动气象站(AWS4600，AWS5500)、三个降水观测点及浅冰芯净积累量数据，着重分析冰川区气温和降水的时空变化特征。气温资料显示本区具有消融期较长的特征，且冰雪区气温递减率年内变化与山区相反。降水方面，本区降水量丰富，冰芯记录的积累区多年平均降水量达到2400mm以上，降水季节分配的显著特点为春季降水所占比例较大。空间分布上不仅表现为南北坡降水量由于山脉阻挡效应有很大的差别，而且在同一侧冰川区与非冰川区也存在较大差别。（2） 冰川变化及物质平衡对于气候变化的敏感性分析对本区四条监测冰川的物质平衡，冰川后退和面积变化，冰川运动速度及12号冰川厚度等进行了一系列工作来研究本区冰川的变化特征及其对气候变化的可能响应。结合物质平衡实地观测及降水年内分配情况,分析了本区冰川物质平衡年内过程与青藏高原其它冰川的异同点，结果显示本区冰川区别与典型的暖季补给型冰川，夏季是物质亏损最强时期，而春季降水对于冰川的补给作用较强。咎其差异的原因主要是由于降水的年内分配差异及水热条件不同所造成的。物质平衡观测数据显示近期冰川都处于亏损状态，05/06物质亏损严重，而06/07年物质亏损相对较弱，两年物质平衡数值存在明显的差异，分析结果表明暖季气温的变化及由其导致的冰川表面物理性质改变是造成物质平衡变化差异的主要原因。以帕隆94号冰川为例，利用度日物质模型模拟其物质平衡变化。假定06/07物质平衡年为多年平均状态，讨论了不同气候情景下，冰川表面物质平衡的变化情况，结果表明冰川对于气温变化敏感性要远远强于降水，降水不变的情景下，气温升高1度导致平衡线上升127m, 而气温不变的情况下，降水增加20%，平衡线仅下降16m, 未来气温升高1度，降水增加20%冰川平衡线将上升95m,冰川的萎缩态势仍将继续。此外，结合野外观测及遥感资料分析，四条冰川都表现为明显后退与面积减小。而通过两年的物质平衡数据及12号冰川测厚数据，粗略推断该冰川可能在未来数十年内消失。小冰期以来冰碛序列及野外地衣直径表明，可能在19世纪初期冰川规模达到近几百年来的最大规模，而气温升高仍是本区冰川萎缩的主要控制因子。（3） 冰川区水文特征及其对气候变化的响应根据帕隆4号冰川流域及然乌湖水文资料，分析本区冰川径流和湖泊水文特征，同时对冰川径流变化过程进行尝试性模拟，讨论其在未来不同气候变化情景下的响应。结果表明：帕隆4号冰川径流波动主要受到气温控制，由于流域处于雨影区且冰川消融强烈，所以季风降水对于径流的贡献率相对较小，仅占9%左右，强季风降水并不会造成本流域径流突然增大，且径流的日内波动表现为峰型尖瘦，与其它典型性海洋性冰川有所差别。就冰川径流与然乌湖水位变化而言，冰川径流与湖水水位之间存在高度相关，但是消融初期由于湖泊的排泄能力有限，会形成雍水，之后湖泊水位保持较小波动。最后，利用度日消融模型及线性汇水模型，把本区冰川DEM，气温，降水，积雪变化情况作为输入值，以小时为单元模拟观测期间冰川径流，取得了较好的模拟效果。通过对不同气温和降水变化情景下径流的变化模拟表明：气温升高所引起的径流增大比例要远远强于降水，1℃的升温会引起42.7%的径流增加，而降水量对于径流量的影响则不太明显，降水增加25%引起的径流量增大仅2.8%左右.
In response to global warming, glaciers on the Tibetan Plateau showed a dramatic retreating trend. Temperate glaciers in the southeast Tibetan Plateau is one of glaciated centers in China. These maritime glaciers are sensitive to climate change and capture the warm and humid moisture while the southwest monsoon penetrates into the Tibetan Plateau. Thus, it is a possible approach to improve the understanding of the relationship between glaciers and southwest monsoon by studying the variation of maritime glaciers in this region. In addition, the glacier variation is also related to the changing water resources and water-related disasters which will impact the local sustainable development. In order to clarify how temperate glaciers respond to climatic change and the hydrological characteristics of the glaciers in this region, a glaciological, hydrological and meteorological investigation was carried out in the Gangrigabu Mountains by Institute of Tibetan Plateau Research, CAS since May, 2006. Based on these data obtained in this survey, this dissertation analyses the meteorological, hydrological and glaciological characteristics in the Ranwu Lake region. This dissertation put emphasis on the following three aspects: 1) Characteristics of temperature and precipitation in glacier region According to temperature recorded by two automatic weather stations (AWS4600 and AWS5500), precipitation data in three observation points and net accumulation data derived from ice core in the altitude of 5500m, the spatial and temporal characteristics of temperature and precipitation are analyzed. The AWS data proves that the number of days which daily mean temperature above zero degree is more than five months. It means the relatively long ablation period than the glaciers in interior Tibetan Plateau. The temperature lapse rate calculated by two AWS is totally different with that calculated by meteorological data from Bomi and Zayu with AWS4600. These imply that we should select proper lapse rate for temperature extrapolation from low altitude. With regard to precipitation, abundant precipitation occurs in this region. Net accumulation recorded by ice core in 5500 m a.s.l. proves that the average annual precipitation from 1998 to 2005 is more than 2400mm and precipitation lapse rate is great in this region. Precipitation mainly concentrates during March-October and the snowfall in spring accounts for lager proportion of precipitation. Not only the spatial distribution on the South and North Slope vary greatly because of foehn, but on the same side of the Ranwu Lake region there are also very different pattern. A decreasing trend from Ranwu Lake to the glacier terminus and an increasing trend from glacier terminius to the glacier surface are observed in this region. It means that in high mountains great change in precipitation could happen in a short distance. Precipitation near Ranwu Lake concentrates at night while most of precipitation occurs in the daytime near glacier region. Such discrepancy should be attributed to strong convection around glaciated region. 2) Glacier variation and the sensitivity of mass balance to climate change A combined investigation by glacier mass balance observation, glacier terminus position measurement, glacier surface velocity survey, glacier Ground Penetrating Radar, topography maps and RS satellite images, was made on four monitored glaciers in the southeast Tibetan Plateau, in order to study glacier variation and their response to climate change. Combining mass balance observation in the field with the distribution of annual average precipitation, the similarities and differences of mass balance process between maritime glacier in this region and glaciers in other place are analyzed. The discrepancy is due to the distribution of rainfall during the year and different thermal and water condition in different regions. Glaciers in this region are characterized by great mass loss in summer and relative great accumulation in spring. But the accumulation and ablation in other region concentrates simultaneously in summer which is so called summer-accumulation type. Mass balance data shows that all monitored glacier are in a deficit condition in the past two balance years. The mass balance in 2005/2006 is more serious than that in 2006/2007, which should be attributed to the variation in summer temperature and glacier surface physical condition. Taking Palong No.94 Glacier as an example, the mass balance variation since June 2006 is simulated by the degree-day glacier mass balance model on the assumption that mass balance in 2006/2007 represents average state for many years. In the sensitivity test it is found that air temperature and precipitation play different impacts on mass balance formation. The ELA rising of about 127m can be expected for a 1K warming, and about 20% of precipitation increase can force the ELA lowering of 16m. The climatic scene of 1K warming and 20% precipitation will lead to about 95m increase in ELA. In such condition, the glacier shrinkage trend will continue. Meanwhile, combination of field observation and remote sense data analysis, the results showed that four monitored glaciers have significantly retreated and reduced their area. With recent mass balance data and glacier depth measured by Ground Penetrated Radar, it is expected that the No.12 Glacier could be disappeared in the next few decades if recent climatic trend continues. The analysis of meteorological data in Bomi and Zayu meteorological stations imply that temperature rising is still the controlling factor which lead to glacier shrinkage. 3) The glacier hydrological characteristics and its response to climate change Based on the hydrological data collected in the Palong No.4 Glacier basin and Ranwu Lake, the hydrological characteristics in this region is analyzed and its response to climate change is also discussed. The glacial discharge is mainly controlled by air temperature. Glacier runoff mainly concentrates in July and August when the strongest ice ablation occur. The time lag between air temperature and discharge usually ranges from 1 to 3 hours. Monsoon rainfall accounts for only 9% of total discharge. Strong monsoon precipitation does not bring strong rainfall hydrological pattern. There is good correlation between glacier discharge and lake water level. However, in the early ablation period, the highest lake water level happens due to limited capacity of discharge from Ranwu Lake. After that, lake water level maintain a high level and smaller fluctuation. Finally, simulation of the glacial discharge by degree-day model and linear reservoir routine model is made to make clear how the melt water runoff response to the climate change. We take DEM, temperature, precipitation, snow area as input parameters, the hourly-discharge is simulated and achieved good results. This paper forecast that the runoff volume will increase 42.7% with 1℃ increase and about 2.8% increase with about 25 percent increase in precipitation.
|MOST Discipline Catalogue||理学::地理学|
|Table of Contents|
|杨威. 藏东南然乌湖地区冰川变化与径流特征研究[D]. 北京. 中国科学院研究生院,2008.|
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