KMS XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY，CAS
| 天山积雪变化及驱动机制研究 | |
| Alternative Title | The snow cover change in Tienshan Mountains and it’s driving forces |
| 李玉朋 | |
| Subtype | 博士 |
| Thesis Advisor | 陈亚宁 |
| 2020-06-30 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 理学博士 |
| Keyword | 气候变化 天山物候 积雪物候 降雪 MODIS Climate Change Snow Phenology Tienshan Mountains Snowfall MODIS |
| Abstract | 天山地处欧亚腹地， 横亘中国新疆中部，连接中亚的哈萨克斯坦、吉尔吉斯斯坦和塔吉克斯坦，全长 2500 km2， 是对全球气候变化响应最敏感地区之一。 在过去半个世纪， 天山作为中亚水塔， 升温速率高达 0.34℃/10a， 显著高于同期全球增温速率和北半球增温速率。 温度的升高， 不仅加快了天山地区以冰川、 积雪为主体的“固体水库”的消融和萎缩， 改变了融雪水文过程和径流组分， 同时， 升温还导致天山山区降雪的时空分布和降水形式改变， 对天山地区的水资源系统产生着重要影响。本文基于 MODIS 数据， 采用 Terra 和 Aqua 的结合以及临近日分析、空间分析以及与 IMS 相结合等方法去云， 研制出一套天山地区无云日积雪产品；解析了气候变化对天山积雪物候的影响以及积雪物候与气候、 海拔的关系；分析了气候变化背景下的降雪率变化机理及可能影响； 并基于高分辨率的统计降尺度的NEX-GDDP 数据， 调查分析了天山及周边山区的降雪量、降雪天数在 RCP4.5 和RCP8.5 的变化及驱动机制， 并对未来情景下的降雪变化趋势进行了预估。 论文主要进展和结论如下：（1）MODIS 具有较高的空间和时间分辨率，但受到云的遮盖限制了其应用。交互式多传感器雪冰测绘系统（IMS）的积雪产品可以穿透云层，但它的空间分辨率较粗。基于上述两个积雪产品优势和劣势，本研究结合了 MODIS 和 IMS 的优势来创建一种改良的积雪产品，该产品既不受云干扰，又具有较高的时空分辨率。改进后的 MODIS 积雪产品数据的年平均积雪量比原始的 MODIS 积雪产品高了 31.5%。此外，与台站的积雪观测深度相比，改进后的积雪产品的总体精度，陆地精度和积雪精度分别为 88.2%， 91.9%， 81.9%。鉴于改进后的 MODIS 精度准确性的显着提高，该产品可应用于天山气候变化研究和雪灾监测。（2） 关于天山地区积雪面积和深度的研究较多，但对气候变化下天山积雪物候变化的调查研究尚缺乏。我们依靠 MODIS 每日无云积雪百分比产品调查了天山地区在水文年 2002/03-2017/18 期间的积雪物候参数（SCD， SOD 和 SED）的时空变化并调查了积雪物候与气候和海拔的关系。研究表明： SCD， SOD 和SED 随海拔变化的平均梯度分别为 6.0， -2.55 和 3.44d/100m。由于太阳辐射和水汽来源的差异，与朝南地区相比，朝北地区通常具有更高的 SCD，更早的 SOD和更晚的 SED。同样，在高海拔和低海拔的积雪物候参数趋势也显示出相反的变化。与近年来的积雪面积增加一致，整个天山地区的 SCD 不显著的增加趋势，尤其是在天山北部。相较于 SED 的提前，延长的 SCD 与 SOD 的提前关系更大，这主要于近些年秋季气温下降和降水增加导致的积雪积累增多有关。（3） 在气候变暖的情况下， 降水形式发生了改变，导致降雪率降低。 而降雪率降低显著影响山区产汇流过程，甚至水资源量。本文采用阈值温度法，结合多源资料（APHRODITE、 CPC 和气象站）分析， 解析了 1960-2017 年中亚天山地区的降雪率变化。结果表明，气温升高引起天山地区的降水形式由降雪向降水转变。 S/P 总体呈下降趋势，在 1990 年代中期之前以 0.6%/十年的速度上升，随后以-0.5%/十年的速度下降。 S/P 下降主要发生在中低海拔（1500～3500m），在海拔较高（超过 3500 米）时，由于温度始终低于冰点， S/P 比值降低的幅度很小，甚至增加。 S/P 的降低总是与冰川/融雪补给河流的年流量减少密切有关。（ 4） 我们评估了 RCP4.5 和 RCP8.5 排放情景下， 2075-2099 年相对于1976-2005 年的平均降雪量（S_mean），降雪天数（S_d）和降雪率（S_f）的变化。评估表明，尽管 NASA 的 NEX-GDDP 高分辨率的每日降尺度数据集可以成功捕获平均降雪气候的分布，但它对极端降雪的刻画有较大的误差。未来随着温度升高，尤其是冬季温度的增加，在 RCP4.5 和 RCP8.5 排放情景下， 会导致降雪量分别减少 18.9%和 32.8%，降雪天数减少 29.6%和 47.3%， 降雪率减少 26.7%和 42.3%。此外，在高排放情景下，以降雨为主的地区预计将扩大到 53.9%，而以降雪为主的地区则会仅占整个高亚洲的 17.9%。从空间上看，高亚洲东部的东天山、 东昆仑、 祁连山以及南部和东部西藏及横断山一带的降雪率降幅比西部的帕米尔高原和喀拉昆仑山的降幅更大。 这种差异可归因于基准温度、 海拔高度以及“Karakoram 异常”（异于其他冰川区冰川退缩的现象）。 |
| Other Abstract | Tienshan Mountains are located in the hinterland of Eurasia, across the centralXinjiang of China, connecting Kazakhstan, Kyrgyzstan and Tajikistan in Central Asia,with a total length of 2500 km2. It is one of the most sensitive regions to respond toglobal climate change. In the past half century, as a water tower in Central Asia, thetemperature rise rate of Tienshan Mountains has reached 0.34 °C/decade, which issignificantly higher than the global temperature rise rate and the Northern Hemispheretemperature rise rate in the same period. We anticipate that rapid warming could altersnowmelt water processes, accelerate the melting of snow, shift precipitation fromsnow to rain, and cause the mutual feedback of decreased surface albedo of snow andsnowmelt water, thereby affecting the recharge of runoff and water resources.In this study, partial clouds appearing in the Moderate Resolution ImagingSpectroradiometer (MODIS) were removed by temporal and spatial filtering, and theremaining cloud pixels were replaced by Interactive Multisensor Snow and IceMapping System (IMS); The influence of climate change on snow phenology and therelationship between snow phenology and climate, altitude are analyzed; Themechanism and possible influence of snowfall rate under the background of climatechange are analyzed; Based on the high-resolution statistical downscalingNEX-GDDP data, the change and driving mechanism of snowfall amount andsnowfall days in RCP4.5 and RCP8.5 in Tienshan and surrounding mountainous areasare investigated and analyzed, and the snowfall trend in the future scenario ispredicted. The main progress and conclusions are as follows:(1) MODIS has a high spatial and time resolution but always obscured by cloud.While the IMS snow cover product can penetrate cloud but has coarse spatialresolution. In response to these strengths and limitations, this study combines MODISand IMS to create an improved snow product which is both free from cloudinterference and features high temporal and spatial resolution. The novel compositesnow-mapping product is then applied over the Tienshan Mountains region in CentralAsia. The retrieved annual mean snow cover for the improved MODIS product data is31.5% higher than the original MODIS product. Furthermore, compared with in-situsnow depth measurements, the overall accuracy, land accuracy and snow accuracy ofthe improved snow product is 88.2%, 91.9%, 81.9%, respectively. Given the significant improvement in its accuracy, this product can readily be applied to climatechange research and snow disaster monitoring.(2) Although previous studies have characterized changes in seasonal snow coveror made predictions about snow cover in a changing climate, no comprehensivespatiotemporal analysis of snow phenology has been presented for the TienshanMountains, Central Asia. Relying on daily cloud-free snow cover fraction productsoriginating from Moderate Resolution Imaging Spectroradiometer (MODIS) for2002/03-2017/18, the snow phenology parameters (i.e., SCD, SOD, and SED) arederived for each hydrological year within the study period and the characteristicsanalyzed for the Tienshan Mountains. The spatiotemporal changes of snow phenologyhave strong altitude dependence. The mean gradients of SCD, SOD, and SED withelevation are 6.0, -2.55, and 3.44 d/100 m, respectively. Because of differences insolar radiation and water vapor sources, the north-facing areas generally have a higherSCD, earlier SOD, and later SED than south-facing areas. Also, the trends of the snowphenology parameters at high and low altitudes show opposite changes. Consistentwith the increase in snow cover area in recent years, SCD for the entire Tienshanregion showed a clear uptick, especially in Northern Tienshan. This prolonged SCDwas more related to advanced SOD than to SED, as decreased temperature andincreased precipitation in autumn are conducive to snow accumulation.(3) In a warming climate, precipitation (p) is less likely to occur as snowfall (S).change in the snowfallfraction (S/P) is currently assumed not only influences theaccumulation and ablation of glaciers, but also influences the streamflow and waterresources significantly in mountainous regions. However, until now, most studieshave focused on precipitation magnitude and its frequency changes, while seasonalshifts in precipitation types have been mostly neglected. This paper employs thethreshold temperature method in combination with multi-source dataset(APHRODITE, CPC and meteorological stations) analysis to determine snowfallproportions in precipitation in the Tienshan Mountains, central Asia, during 1960–2017. The results indicated that temperature-induced precipitation shifting from snowto rain. The S/P experienced an overall declining trend, increasing at a rate of0.6%/decade prior to the mid-1990s, followed by a downward trend at a rate of−0.5%/decade. The S/P decreased mainly at low and middle altitudes (between 1500and 3500 m). At higher altitudes (over 3500 m), the magnitudes of the decreased S/P ratios were small or even increased due to the temperature always being belowfreezing. Decreases in S/P are always associated with decreases in annual streamflowin the glacier/ snow melt recharged rivers.(4) High Mountain Asia (HMA), which includes the Tibetan Plateau, TienshanMountains and surrounding region, has abundant snowfall with a long period of snowcover annually. The headwaters of many prominent Asian rivers depend in part onHMA meltwater. We evaluated projected changes in mean snowfall (S_mean),snowfall days (S_d), and snowfall fraction (S_f) for 2070-2099, relative to the1976-2005, under the RCP (Representative Concentration Pathway) 4.5 and RCP8.5emission scenarios. An evaluation of the results shows that while NASA’sNEX-GDDP (National Aeronautics and Space Administration Earth Exchange GlobalDaily Downscaled Projections) high-resolution daily downscaled dataset cansuccessfully capture the distribution of mean snowfall climatology, it has a strong biasfor extreme snowfall indices. In general, the projected increase of temperatureespecially in winter (under RCP 4.5 and RCP8.5) will result in a decrease in snowfallamount (-18.9%, -32.8%), fewer snowfall days (-29.6%, -47.3%), and lessprecipitation falling as snow (-26.7%, -42.3%). Furthermore, under high emissionscenarios, rain-dominated regions are projected to expand to 53.9%, while thesnow-dominated areas only account for 17.9% of the entire HMA. Spatially, thesnowfall shows a more robust decline in the eastern HMA (e.g., East Tienshan, EastKun Lun, Qilian, South and East Tibet, and Hengduan) than in the western HMA (e.g.,Hissar Alay, Pamir, and Karakoram). This difference can be attributed to variousenvironmental factors, such as baseline temperature, elevation, projected changes intemperature, and the “Karakoram anomaly”. |
| Subject Area | 自然地理学 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xjlas.org/handle/365004/15434 |
| Collection | 中国科学院新疆生态与地理研究所 研究系统 |
| Affiliation | 中国科学院新疆生态与地理研究所 |
| First Author Affilication | 中国科学院新疆生态与地理研究所 |
| Recommended Citation GB/T 7714 | 李玉朋. 天山积雪变化及驱动机制研究[D]. 北京. 中国科学院大学,2020. |
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