格陵兰冰盖表面水系形态特征与融水输送效率遥感研究

The Greenland ice sheet (GrIS) is the second largest ice body on the earth. In the last two decades, the GrIS has undergone an accelerated loss of mass. Significantly increased surface melt leads to the formation of large patches of supraglacial river networks on the ice sheet surface each melt season. A better understanding in these river networks is crucial to learn supraglacial hydrologic processes and consequently the ice sheet mass balance. This project aims to study the GrIS supraglacial river networks by combining multi-source, multi-spatial-resolution earth observational images (e.g., Landsat ETM+/OLI、ASTER、WorldView-1/2/3、Radarsat-2) with field observational data. Prime attention is paid to address the fundamental problems in the GrIS supraglacial hydrology research, such as feature extraction, feature analysis, and key hydrologic parameter calculation. First, supraglacial river networks are automatically delineated and subsequently mapped. Second, their morphometric and hydraulic characteristics, such as stream order, drainage density, river width, depth, velocity, and slope, are studied. The final goal of this project is to answer the following scientific questions: 1) what are the morphometric characteristics of the supraglacial river networks? 2) where is surface meltwater released on the ice sheet surface and what are the distribution principles of these release locations? 3) to what extent does ice surface topography dominate the movement of water across the ice sheet? 4) how efficiently is GrIS surface meltwater transported off the ice sheet surface? The results will improve our understanding in the supraglacial hydrology and mass balance of the GrIS.

格陵兰冰盖是世界第二大陆地冰盖，近二十年来处于物质损失加速的状态。每年消融期在格陵兰冰盖表面会形成规模庞大、结构复杂的冰面水系。掌握冰面水系输送与释放融水的方式和效率，对于理解格陵兰冰面水文过程，进而准确分析冰盖物质平衡具有重要意义。本项目综合Landsat ETM+/OLI、ASTER、WorldView-1/2/3、Radarsat-2等多源、多空间分辨率卫星遥感影像和实地测量数据，解决冰面水系研究中特征提取、特征分析、关键变量计算等难点，构建冰面水系遥感自动提取方法，完成冰面水系专题制图，研究河流等级、水系密度、河宽、水深、流速、河流比降等一系列形态与水力几何特征，最终回答：①格陵兰冰面水系具有怎样的形态特征？②格陵兰冰面融水释放的空间位置具有什么规律？③格陵兰冰面地形如何影响冰面水系形态？④格陵兰冰面水系输送融水的效率如何？等科学问题，提升对冰面水文过程与冰盖物质平衡的理解。

格陵兰冰盖是世界第二大陆地冰盖，如果格陵兰冰盖全部消融，全球海平面将上升约7米。近几十年来，格陵兰冰盖加速消融，已成为对全球海平面上升贡献最大的单个冰体，深刻影响温盐环流等全球海洋环境，对人类应对全球气候变化、实现可持续发展提出重大挑战。同时，我国提出打造“冰上丝绸之路”，开发利用北极航道。格陵兰临近西北北极航道，冰盖消融将显著影响北极航道通航条件，进而深刻改变全球贸易格局。格陵兰冰盖消融是极地与海洋两个“战略新疆域”的交叉领域，具有重要研究意义。本项目利用高空间分辨率卫星遥感影像，开发了冰面水系处理程序集，完成了全格陵兰冰盖消融区冰面水系专题制图，分析了格陵兰冰面水系形态特征，揭示了冰面水系与陆地水系的异同，分析了格陵兰冰面水系融水输送效率，提出了一种测算冰面径流量的新方法，揭示了目前常用的区域气候模式过高地估算了冰面实际径流量，并且没有考虑冰面融水输送产生的延迟效应，规模庞大、结构复杂的冰面水系实际控制着冰面融水输送的方式和效率，对于冰盖物质平衡具有重要影响。格陵兰冰面水系融水输送效率分析研究成果以封面论文的形式发表在PNAS。2017年纽约时报报道了项目研究进展，2018年新华网也报道了相关成果。