复杂地形和局地因素复合作用下江河源区地面温度特征和冻土模型研究

The Qinghai-Tibetan Plateau (QTP) is the highest and most extensive elevational permafrost region on Earth. Most plateau permafrost is warm (>–1 °C) and sensitive to climate changes and anthropogenic activities. The geographical and climatic background play the key roles in controlling the macro spatial distributive patterns of permafrost on the QTP. However, under certain conditions and spatiotemporal scales, the combined influences of the rugged topography and other local factors (such as the vegetation, soil types, and so on) turn to be the primary factors in controlling the distribution of elevational permafrost through their influences on the ground surface temperatures (GST). While the GST is the upper boundary condition of thermal regime of the active layer and permafrost and a key parameter in the permafrost-climate system. Based on previous permafrost-climate monitoring network and related studies, a GST monitoring network will be built according to the elevation, slope angle and aspects, curvature, and shading, as well as the vegetation and thermophysical properties of soils in representative areas in the Source Regions of the Yangtze and Yellow River (SRYYR). Based on the detailed field experiments and investigations of key terrestrial parameters, more accurate retrieval of remote sensing products about the topographic and vegetation indices derived from the MODIS, Landsat series and Aster DEM will be implemented. The combined thermal impacts of the rugged topography and other local factors on the GST will be quantitatively studied. Then, the explicit relationships will be conceptualized between the permafrost and climate in the SRYYR. Based on the geophysical investigations, such as the Electrical Resistivity Tomography (ERT) and Ingegneria Dei Sistemi (IDS), and ground-truthing, as well as the existing scientific datasets, and collections of air, ground surface, and ground temperatures from the newly established monitoring network, the performance and uncertainty of equations and methods related to the modelling of permafrost distribution such as the Stefan equation, Kudryatsev’s method, TTOP model, and heat transfer equations will be carefully evaluated for the complicated terrain conditions and other environmental variables. At last, the elevational permafrost model coupled with the rugged terrain indices and other local factors will be built. The project results will provide sound experimental basis for the applications of huge amounts of land surface temperature (LST) products, which are inferred from the thermal infrared remote sensing, in cryospheric science and technology, e.g., permafrost mapping and modelling will be evaluated. In addition, it will provide scientific supports for obtaining the key parameters of better mapping of elevational permafrost at finer scale, and further contribute to the adaption to climate change, ecological restoration and environmental management in the SRYYR.

青藏高原高海拔多年冻土居世界之首，大的地理和气候背景决定了其宏观分布格局，但复杂地形和局地因素通过对冻土气候关系体系关键因子之一—地面温度—的复合影响，在一定条件下甚至成为其空间分异的主导因素。本项目拟在试验点、监测场和研究区等不同空间尺度上布设江河源区地面温度定位观测，并针对地面关键参量进行野外试验和空间数据反演，以定量分析复杂地形和局地因素对地面温度的复合作用。在此基础上，确定高海拔山区地面温度各指标的时空分布，建立地面温度对多年冻土存赋的判据。基于观测和调研资料、坑探/物探等，验证Stefan经验公式、Kudryatsev方法、TTOP模型、传热方程等冻土模型方法在高海拔山区的适用性。最终构建耦合地形和局地因素的高海拔冻土模型并精准制图。本研究可为海量热红外遥感陆面温度的冰冻圈科学应用提供试验依据，进而为三江源区生态修复和生态文明建设等提供科学理论基础。

本项目以江河源区为研究区，针对地面温度强烈空间分异特征，广泛搜集资料，开展定位监测与调查，并结合遥感反演和模型模拟，取得以下结论：. 1）、地面温度是冻土模拟和制图上边界，与气温和冻土温度的定量关系深刻影响多年冻土精准模拟与制图。在查拉坪、查龙穷、野牛沟、清水河以及麻多乡、汤岔玛等地布设地面温度监测网络，包含100个左右的自记式温度计。同时调查了高寒植被并原位及实验室内测量了土壤热物理属性。发现因微地貌和地表覆被不同，地面温度呈现了复杂的空间分异特征。. 2）、高寒草甸是青藏高原多年冻土区两大主要地表覆被类型之一。查拉坪为典型高寒草甸覆盖区，初步厘定了该区气温与地面温度的定量统计关系，获得了逐月地面温度与逐月气温之间的N-系数。发现植被指数对逐时、逐日、冻结融化季及年际尺度的关系。土壤质地和含水量、高寒植被等的复合作用导致年均地面温度在极小空间表现了极强异质性。. 3）、研究了黄河源区多年冻土对气候变化响应模式，发现较低温多年冻土（<–1 °C）升温较快，而高温多年冻土特别是极高温多年冻土（>–0.5 °C）升温缓慢。作为典型高温高海拔多年冻土区的巴颜喀拉山（海拔4220-4830 m），其升温模式并无明显海拔效应。. 4）、暖湿化背景下的强降水增加，使浅表多年冻土升温甚至可能穿透高温多年冻土（>–0.5 °C），从而使得冻土层上水、冻土层间水、冻土层下水形成水力联系，改变局地水文循环结构，加剧多年冻土退化。. 5）、在保持土壤热物理属性一致基础上，分别以气温、陆面温度和地面温度驱动GIPL模型模拟其对冻土热状态影响。发现气温和陆面温度驱动的模拟其年均值偏差在–3 °C以上，尤以冬季温度偏差最大；而地面温度驱动模拟偏差极小。. 本项目的成功实施厘清了第三极特别是高寒草甸覆盖区的冻土—气候关系，为多年冻土热状态的空间分异规律及其精准模拟制图提供了科学依据，为气候变化和强烈人类活动叠加影响下的高寒生态环境稳定和冻土区水源涵养能力提升提供了有力科技支撑。