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天山山区冰雪变化对水储量及径流影响研究
邓海军
学位类型博士
导师陈亚宁
2017-05-01
学位授予单位中国科学院大学
学位授予地点新疆乌鲁木齐
学位专业理学博士
关键词气候变化 水储量 径流 水量平衡模型 天山
摘要山区是一个独特的地理单元,以冰川和积雪为主要存在形式的固态水资源储量丰富,是众多大江大河的源地。冰川是气候系统的重要组成部分,冰川和积雪覆盖面积的变化对流域水文过程有重要影响。气候变化加速了中纬度山区的冰川退缩和积雪消融。但冰川和积雪面积的缩减对高寒山区的气温升高存在放大效应。中亚天山平均海拔超过 4000 米,在空间上对气温和降水起到重新分配的作用,并储藏有大面积的冰川和积雪,是中亚地区河流的源地,被称为“中亚水塔”。受全球气候变化的影响,天山山区的冰川一直处于退缩状态,尤其是天山中部区域。同时天山的气象观测点稀少,仅有的站点建站时间短不能满足对整个中亚天山的研究,因此当前对天山的研究主要集中在局部区域。观测资料的缺乏,是当前评估气候变化对该区域水资源影响的主要挑战。缺乏对高亚洲区域的水文机制的认识是评价气候变化对该区域水文水资源影响的主要不确定性因素。本文分析了天山山区气温、降水、积雪、冰川及水储量的变化,探讨了气候变化对天山山区水资源的影响机制,构建了适合于高寒区域径流模拟的水量平衡模型,预估了不同气候变化情景下流域径流的可能变化趋势,为科学辨识气候变化对天山山区水资源的影响机制,以及流域尺度的水资源综合管理具有重要参考价值。主要研究结论归纳如下:(1)近半个世纪以来天山山区的气候变化以暖-湿化趋势为主天山山区气候变化研究是基于 APHRO’s 和 ECWMF ERA 数据集,发现天山山区从 1980s 中期开始升温,到 21 世纪初平均气温已接近 5℃,上升了接近了 1℃;从气温空间变化特征来看,整个天山山区在过去 50 年中以升温为主,大部分区域升温幅度在 0-0.04 ℃/a 之间。天山山区的降水变化表现为天山中、东部降水呈增加趋势,增加速率在 0-1.5 mm/a 之间,而天山西部降水呈减少趋势,最大减少速率在-2- -6 mm/a左右,主要位于伊塞克湖流域。3000 米海拔以上区域随气温的升高降雪以增加趋势为主,而 3000 米海拔以下区域随气温的升高降雪以减少趋势为主。同时,降雪率的季节变化与气温的变化密切相关,除冬季随气温的升高降雪以增加的趋势为主外,其他季节都是以减少的趋势为主。这表明存在一个气温阈值从某种程度上影响并控制了降雪变化。因此,确定降雪率和降雨率转化的温度区间范围对于研究降雪率的变化具有重要意义。(2)山区以冰雪为主体的固态水库处于持续的亏缺状态在全球变暖的影响下,天山山区的冰川处于退缩状态。自 1970s 以来,天山冰川总面积大约减少了 8.5%,但是不同的区域退缩速度不一样:海拔 3000 米以下区域的冰川退缩速率最大,达到了 2.3×103kg/(m2*yr);3000-4000 米海拔区域的冰川退缩速率次之,大约是 0.6×103kg/(m2*yr);4000-5000 米海拔区域的冰川退缩速率大约为0.3×103kg/(m2*yr);而 5000 米以上海拔区域的冰川退缩速率就非常小。同时,冰川的退缩速率与冰川面积呈负相关,面积越小退缩速率越快,说明小型冰川对气候变化的响应更为敏感,面积大的冰川相对稳定,而天山山区 90%以上的冰川属于小型冰川,因此这一研究结果具有重要的指示意义。积雪覆盖面积同样呈减少趋势,2002-2013 年天山山区最大积雪覆盖率呈减少趋势,减少速率为 0.44%/a,而最小积雪覆盖率变化不明显,减少速率为 0.01%/a(相当于-47 km2/a)。2002-2013 年天山山区年内积雪覆盖历时的递减速率大概为-0.2 day/yr,年内积雪覆盖历时从 2002 年的 216 天,到 2013 年 208 天,缩短了 8 天。年内积雪覆盖历时变短,意味着积雪对年内的水文系统的缓冲作用降低,会使天山山区水资源的变率加大。近 30 年来,天山山区的雪水当量有一个较小的递减趋势,递减速率大约为-0.017 m/a,但没有通过 p=0.05 水平下的信度检验。天山西部区域雪水当量以递减趋势为主,天山东部区域雪水当量以增加趋势为主。(3)气候变化是驱动山区水储量减少的主要原因GRACE 重力卫星数据为研究山区水储量的变化提供了数据支撑,研究结果表明,2003-2015 年期间天山山区大部分区域的水储量减少速率小于 1 cm/a。但是,天山山区中部偏东区域表现水储量的急剧减少,减少速率达到 4-8 cm/a。春季水储量为正距平,是因为天山山区整个冬半年固态水资源一直处于积累过程,到春季的时候这种积累达到最大值,因此春季的一直为正距平。同样,夏半年一直处于消融过程,到秋季的时候达到消融的最大值,因此水储量在这个季节表现为负距平。冬季和夏季处于正、负距平的过渡阶段,是因为气温和降水组合的年际差异导致的。气候变化是天山山区水储量变化的主要驱动力。山区变暖导致了山区冰川退缩和积雪消融,进一步驱动山区水储量变化。(4)不同气候排放情景下径流变化差异显著开都河流域、阿克苏河流域以及乌鲁木齐河流域的径流变差系数 Cv 值位于0.1~0.2 之间,这是因为冰川和积雪融水对流域径流变化的调节作用。径流分析以基于水量平衡模型为工具。本文通过将冰川物质平衡因子嵌入到水量平衡模型中,模拟径流变化,结果表明,开都河流域的 Nash 效率系数为 0.76,阿克苏河流域和乌鲁木齐河流域的 Nash 效率系数分别达到了 0.8 和 0.86。因此这一方法提高了水量平衡模型在高寒山区的模拟精度。并结合 IPCC AR5 气候排放情景,预估 2020-2100 年这三个流域的径流变化,模型的预测结果表明,在中低排放情景下径流的变化相对稳定,变化幅度较小,但是在高排放情景下径流的变化幅度较大,特别是在 21 世纪中叶以后呈减少趋势。同时发现,冰川面积越大的流域,在气候变化驱动下径流呈减少趋势发生的时间来的越晚,这是因为冰川对水资源的变化具缓冲作用。
其他摘要Mountain regions as a particular geographic unit and are an important water source area. The mountains hold one of larger areas of permanent snow and glaciers, and all of the rivers in the surrounding region originate in the mountains. Glaciers as important parts of the climate system. Glaciers and snow cover area variations also have important effects on hydrological processing in the river basin scale. Climate change accelerates glaciers retreat and snow melt in the mid-latitude mountains. But glaciers and snow cover area changes can reduce also amply temperature increase in the high mountains.The average elevation of the Tienshan Mountain exceeds 4000 m. The mountain holds larger areas of permanent snow and ice, and all of the rivers in the surrounding region originate on the Tienshan Mountain in the central Asia. Climate change effect on glaciers retreats in the Tienshan Mountain, especially in the Centre part of Tienshan Mountain.However, the meteorological observation stations are sparse in the Tienshan Mountain, and only stations observation time too short to study climate change in whole Tienshan.Therefore, observation data inadequate is a major challenge to evaluate climate change effect on region’s water resource. The lake understanding of hydrological mechanisms in the Tienshan mountain regions is a major uncertainty source to assess the impact of climate change on hydrological and water resources. In this paper, analyze changes of temperature,precipitation, snow cover, glaciers and water storage in the Tienshan Mountain, discusses the influence mechanism of climate change on water resources, constructs a water balance model to modelling runoff changes in alpine regions, and forecasts trend of runoff in river basin scale under different climate scenarios. These results have a great reference value for scientifically understanding the impact mechanism of climate change on water resources and water resources integrated management at watershed scale. The main results as following:(1) The dominant climate change trends showed warm –wet trend during nearly half century in Tienshan Mountains Climate change in Tienshan Mountains was analyzed based on datasets, APHRO’s and ECWMF ERA. Results showed that the temperature was rising in Tienshan Mountains since the middle 1980s, the average temperature approached 5℃ till 21st century, and the rising temperature was up to 1℃. According to the characteristics of spatial-temporal changes in climate, there mainly exhibited an increasing trend in the whole Tienshan Mountains during the past 50 years, the rising temperature in most regions was in the range of 0-0.04℃/a. Meanwhile, the annual average temperature and the seasonal average temperature were all decreasing since 1998. The spatial-temporal changes in precipitation showed that there was an increasing trend in the middle and eastern Tienshan Mountains,the rising rate was in the range of 0-1.5 mm/a, while there was a decreasing trend in the western Tienshan Mountains, the maximum decreasing rate was about -2- -6 mm/a, which was mainly appeared in Issyk-Kul basin.Regions of elevations above 3000 meters, the snowfall showed an increasing trend with the temperature rising; while regions of elevations below 3000 meters, the snowfall showed a decreasing trend with a temperature rising.At the same time, the seasonal variation of snowfall rate was closely related to the temperature variations, except for the increasing trend of snowfall with the rising temperature in winter, the snowfall in other seasons mainly showed decreasing trend with the rising temperature. This indicates that the temperature threshold is an important factor to control the snowfall variation. Therefore, it is of great importance to determine snowfall rate based on the temperature range of snowfall transformed into rainfall the temperature.(2) The solid reservoir with ice and snow in the Tienshan mountainous are in a continuous deficit state Under the influence of global climate warming, the glaciers in Tienshan Mountains were retreating. Since the 1970s, the total area of Tienshan glacier had reduced by 8.5%,while the retreat rates of glaciers were various between different regions. Regions of elevations below 3000 meters showed the largest retreat rate of glaciers, reaching 2.3×103kg/ (m2*yr). Followed by those regions of elevations between 3000-4000 meters, about 0.6×103kg/(m2*yr). Regions of the elevations between 4000-5000 meters, the retreat rate of glaciers were about 0.3×103kg/(m2*yr), while the retreat rate was relatively low in regions above 5000 meters. At the same time, the retreat rate of the glacier was negatively correlated with the glacier area variations, the smaller the areas, the faster the retreat rate will be, which indicated that the small glacier was more sensitive to climate change,glaciers with large areas were relatively in a stable state. The snow cover area was showed a decreasing trend, the maximum snow cover exhibited a downward trend in Tienshan Mountains during 2002-2013, the decreasing rate was 0.44%/a; the minimum snow cover variation was not obvious, the decreasing rate was 0.01%/a(equal to -47 km2/a). During the period of 2002-2013, the snow cover time in Tienshan Mountains lasted for about -0.2day/yr, and the snow cover time ranged from 216 days in 2002 to 208 days in 2013, which appeared a shortened time about 8 days. During the year, the snow cover time became shorter, which means that the relieving effect of the snow cover on the hydrological system was reduced. In recent 30 years, the snow water equivalent in Tienshan mountain area showed a smaller decreasing trend, and the decline rate is about -0.017 m/a, while this trend has not been passed the significance test with p=0.05. In the western Tienshan Mountains, the snow water equivalent was mainly decreasing, and the snow water equivalent in the eastern Tienshan Mountains was mainly increasing.(3) Climate change is dominant factor driving the decline of water storage The Gravity Recovery and Climate Experiment (GRACE) mission have provided data that can be used for analyzing water storage variations. The results indicated that terrestrial water storage (TWS) have a decreasing trend from 2003 to 2015 in the Tienshan Mountain,with a decline less than 1 cm/a, but the eastern part of central Tienshan performance a sharp reduction in TWS, reducing the rate of 4-8 cm/a. The TWS had a positive anomaly in MAM because of the solid water resources (glaciers and snow cover) has been in the accumulation process from DJF to MAM, so MAM has been a positive anomaly. Similarly,the summer half of the year has been in the ablation process from JJA to SON, so TWS in this season shows a negative anomaly. DJF and JJA are in the transitional phase of positive and negative anomalies due to the inter-annual differences in combinations of temperature and precipitation. Climate change is the main driving force for changes in TWS in the Tienshan Mountains. The spatial difference of temperature changes has been driven glaciers and snow variations, further driving TWS changes in the Tienshan Mountain.(4) There are significant trends of runoff in the future under different IPCC climate scenarios The Kaidu River basin, Aksu River basin and the Urumqi river basin runoff Cv(coefficient value) value were in the range of 0.1~0.2, this is because the glaciers and snow melt water had a moderating effect on the runoff change. Runoff analysis is based on water balance model. The glacier mass balance factor was inserted into the water balance model,model results showed that the Nash efficiency coefficient of the Kaidu River Basin is 0.76,the Aksu River Basin and Urumqi River Basin are 0.8 and 0.86, respectively. Therefore,the method improved the accuracy of water balance model applied in the alpine region.The results showed that the runoff variation is relatively stable in the middle and low emission scenarios, and the variation range was smaller. However, the runoff variation was very large under high emission scenarios, which showed large decreasing trend, especially in the mid-21st century. At the same time, it was found that if river basin with larger glacier area, will put off the runoff decrease in the future under climate changes, which attributed to the glacier had a buffer effect on the change of water resources.
学科领域自然地理学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14776
专题研究系统_荒漠环境研究室
作者单位中国科学院新疆生态与地理研究所
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邓海军. 天山山区冰雪变化对水储量及径流影响研究[D]. 新疆乌鲁木齐. 中国科学院大学,2017.
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