中国冰川区表碛厚度估算及其影响研究进展

表碛覆盖型冰川是中国西部分布较为广泛的冰川类型,其典型特征是冰川消融区部分或全部覆盖了一层厚度不一的表碛。与裸冰或雪相比,表碛覆盖层下冰的融化过程有独特性,表碛厚度空间分布对一条冰川的消融、物质平衡和径流过程的影响有别于无表碛覆盖型冰川。本文回顾了近年来表碛厚度分布及其影响的研究,通过对这些进展进行总结以进一步明晰表碛影响研究的方向;同时着重介绍了近期发展的基于遥感影像热红外波段和可见光近红外波段、大气—表碛层—冰川界面能量平衡过程的表碛厚度估算方法和表碛覆盖综合评估模型,结合地面观测,分析了以遥感反演的表碛层热阻系数表征表碛厚度的精度,介绍了这类模型在表碛覆盖型冰川物质平衡和径流研究中的应用效果,以及在综合评估流域/区域尺度表碛影响的应用情况,并分析了该模型存在的不足及进一步改进的研究方向,为实现中国西部区域表碛影响的系统评估奠定基础,从而提升对区域水资源和冰川灾害的模拟和预测能力。

Research progress on debris thickness estimation and its effect on debris-covered glaciers in western China

Debris-covered glaciers, characterized by the presence of supraglacial debris mantles in their ablation zones, are widespread in high mountain regions of western China. Supraglacial debris cover on glaciers has the unique thermal process relative to exposed snow and ice, the spatial distribution of which influences both rates and spatial patterns of melting. Due to the debris-cover effect, the responses of debris-covered glaciers to climate change are more complex compared to those of debris-free glaciers. In addition, debris-covered glaciers generally contain a large ice volume, and mass changes of these glaciers are expected to have significant impacts on the regional-scale evolution of river discharge and water resources. However, a better understanding of debris-cover effect in glacier status and hydrology at a regional scale remains a challenge. The difficulty of such a study arises mainly from limited knowledge of the large-scale spatial distribution of the thickness and properties of the debris cover in western China. This study systematically reviews the impacts of the spatial distribution of debris thickness on melting beneath surface debris, mass change and runoff process on debris-covered glaciers. In particular, a physically-based assessment model for debris-cover effect is proposed, which is based on visible and near infrared and thermal infrared bands of remotely sensed data and surface energy-balance process of the debris layer. This model does not require high-quality input parameters related to the extent, thickness and thermal properties of the debris cover, and has been applied to different glaciers of western China for systematically assessing the significance of debris cover and its influence on spatial patterns of ice melting, mass balance and runoff. This approach provides an important insight into exploring the average status of debris-covered glaciers and its impacts on regional water resources in western China. Nevertheless, this approach does not consider the effect of the complex surface composed of co-existing debris-covered ice, bare ice, ice cliffs and supraglacial ponds in the ablation zone, and needs further improvement in the future.