格陵兰冰盖表面融水输送关键过程遥感监测

The transport of meltwater (runoff) is an important hydrological process operating on ablation zone of the Greenland Ice Sheet (GrIS) surface today and is projected to become more prevalent in the future. Runoff generated on the ice sheet surface is typically transported to the bed thus influencing the development of subglacial hydrological system and ice motion. The physical process of surface water runoff on the GrIS therefore warrants study, both for basic scientific understanding and to enable better representation and parameterization of the ice sheet surface runoff in surface mass balance (SMB) models. .The proposed research would use remote sensing, established terrestrial hydrological theory, and SMB models to address three current knowledge gaps about GrIS surface runoff. The principal scientific goals are to validate the accuracy of SMB-modeled runoff; to investigate meltwater transport velocities and time delays in hillslope and channel zones of supraglacial catchments; and to assess whether supraglacial drainage patterns that form on the ice sheet surface can influence subglacial hydrologic systems. .We propose to achieve these goals through conducting a four-part work plan. In brief, the work plan would: Use the volumes of terminal supraglacial lakes, derived from ArcticDEM, Sentinel-2, and Landsat-8, to demonstrate the accumulative runoff produced in supraglacial catchments and thus to validate the accuracy of SMB-modeled runoff; Use two established terrestrial hydrological theories, Unit Hydrograph and Width Function, to quantify optimal meltwater transport velocities in hillslope and channel zones using high-resolution WorldView images and consequently to investigate meltwater transport delays in supraglacial catchments; Conduct variable meltwater inputs to determine the influence of meltwater in the simulations of subglacial and ice flow models; Measure the supraglacial river discharge of the Rio Behar catchment for 3-5 days in field..By the conclusion of the project, we anticipate delivering significantly improved knowledge of surface meltwater routing on the GrIS surface.

格陵兰冰面融水输送显著影响冰盖表面物质损失，融水进入冰盖内部还能够影响冰下水文系统发育。目前，冰面物质平衡模型是研究冰面融水输送的主要手段，但是这类模型缺乏实际观测数据的验证，径流建模结果存在较大不确定性。本项目综合ArcticDEM，Sentinel-2与Landsat-8数据精细测算冰面湖体积，获取长时间、大范围、低成本的冰面径流观测数据，验证冰面径流建模精度；迁移单位线等陆地流域水文学方法，通过高分WorldView影像监测融水输送距离，实地测量冰面水系流量，分析冰面流域融水输送速率与滞时，掌握流域汇流过程；利用不同情景下的流域出口流量驱动冰下水文系统演化，理解冰面融水对冰下水文系统的影响。最终回答如下关键科学问题：（1）冰面物质平衡模型是否准确建模了冰面径流量？（2）如何理解冰面流域汇流关键过程？（3）冰面融水输入是否显著影响冰下水文系统演化？提升对格陵兰冰盖消融机制的理解。

格陵兰冰盖总冰量约7米海平面当量。近20年，格陵兰冰盖物质损失加速，已成为对全球海平面上升威胁最大的冰体。冰面融水径流是造成格陵兰冰盖表面物质损失的主要原因。同时，融水进入冰盖内部，能够驱动冰下水文系统发育，进而影响冰盖运动。然而，准确模拟格陵兰冰面融水径流及其影响十分具有挑战性：冰面融水分布广泛、变化迅速，识别难度大，融水径流通常作为其他区域气候模型变量的残差变量，模拟结果误差大，融水影响冰下水文系统发育的机制尚不清楚，融水加速或减缓了冰盖运动这一基本科学问题尚无定论。本项目观测与模拟冰面融水径流关键水文过程，分析区域气候模型融水径流模拟精度，探索融水进入冰盖内部对于冰盖运动与稳定性的影响，取得了如下研究成果：（1）提出了一种基于终端冰面湖体积的径流量遥感直接观测方法，集成卫星遥感影像与高分辨率数字地形模型，解决了冰面径流量观测时间短、区域小、成本高等问题，揭示了目前常用的区域气候模型都过高估算了冰面径流量；（2）发现了冰面水系与冰面湖共同控制着冰面融水的输送和存储，分析了西南格陵兰冰盖冰面融水动态变化，发现了冰面融水面积与模型模拟的冰面融水径流量呈正相关关系，揭示了冰面流域融水输送速率与滞时；（3）对比分析了综合单位线、重标宽度函数、融水输送-湖泊填充三种冰面融水输送模型模拟流域出口径流过程线的精度，以流域出口的径流过程线驱动冰下水文模型，分析了冰面融水供给对于冰下有效水压的影响，三种冰面融水输送模型均能够较为准确的模拟流域出口的径流过程线，但是在模拟冰面径流峰值大小与滞时长短时存在显著差异。