高寒山区流域水文模型构建及模拟不确定性分析研究

Watershed hydrological model for alpine cold regions has its unique characteristics in model structure, which highlight the changes in infiltration law and water source of evapotranspiration caused by melting processes of glacier, snowpack and frozen soil and their feedbacks. However, people still have no correct and entire cognition with its theory of hydrological model in alpine cold regions, which is immature and still in its early stage. Previous studies suggested that, the runoff scheme in cold region is a combination of saturated runoff (Dunne) runoff and layering runoff above freezing front. Thus, this study focuses on a representative watershed of the Nam Co Basin (Tibet). Based on the the model structure of Xinanjiang hydrological model, a new loose typed hydrological model for alpine cold regions would be established. In this study,the field micro-lysimeter experiment, rainfall simulation and tension infiltration experiment and the laboratory test of soil physical properties will conducted to analyze the law of parameters of soil hydraulic properties and exapotranspiration for typical underlying surfaces. The model employes the depletion of snow coverage to simulate the changes of snow-covered area, and estimates the meltwater of snow and glacier based on the combination of temperature-index degree-day factor and solar radiation. Multisource dataset including ground observed data, precipitation products and remote sensing based evapotranspiration data force the model running and test the applicability of this model in the study basin. In addition, precipitation uncertainty and parameter uncertainty in the model simulation would be analyzed using the Markov Chain Monte Carlo technique.

高寒山区水文模型的构建有其独特性，主要表现为冻融条件改变了水分入渗规律和蒸散发水分来源组成等，产汇流过程也对土壤冻融产生反馈。目前对高寒山区水文模型的理论方法还缺乏完整的认识，模型发展还不成熟。研究表明，寒区流域融冻期的产流以蓄满产流为主、兼有融冻锋面以上分层产流的特点。本项课题以西藏纳木错流域为典型研究区，以新安江水文模型产汇流框架为基础，结合野外小型蒸渗仪观测实验、人工降雨产流实验、张力水入渗实验和室内土壤物理特性测定等分析典型下垫面土壤水力特性和蒸散发的参数规律，构建适用于高寒山区的松散式水文模型。借鉴积雪覆盖衰减曲线概念模拟季节性积雪的空间分布变化；结合基于气温指标的度日因子法与太阳辐射估算冰川和积雪的融化水量；根据地面实测资料、多源降水数据和遥感反演实际蒸散发数据驱动水文模型并检验其适用性。同时，采用马尔科夫链蒙特卡罗抽样技术分析降水不确定性和模型参数不确定性对模拟结果的影响。

长期以来，由于地面监测资料的缺失，青藏高原高寒山区冰雪融化、产汇流及地表/地下水与湖泊水量交换等过程尚不明确；特别是冰川融化、降水和气温变化等对湖泊水位变化的贡献尚难以量化。本项研究以青藏高原内流区纳木错流域为研究区，结合遥感反演下垫面变化、多源降水数据融合及误差分析，从冰川、高寒小流域及冰川-陆面-湖泊系统三种空间尺度研究高寒山区流域水循环过程。重点开展了以下研究：（1）在扎当冰川，构建了基于能量守恒的冰川消融模型，揭示了典型小流域内冰川的能量收支和物质平衡状况，从能量角度分析了冰川持续消退背景下2008年冰川正物质平衡的主要原因。（2）在曲嘎切流域，耦合冰川消融模块，改进了融合蓄满-超渗混合产流机制的分布式水文模型GSSHA，实现在曲嘎切冰川小流域的分布式水文模拟，辨识了降水、冰川融水及蒸发对陆面小流域水量平衡的贡献。（3）在纳木错湖泊流域，建立可模拟冰川-陆面-湖泊水量交换的概念性水文模型Glakewatershed，模拟了1961-2015年间纳木错流域冰川-陆面-湖泊系统的水文过程，重构了月尺度的湖泊水位变化，分析了降水、冰川融水、陆面产流及水面蒸发对湖泊水量平衡的贡献。（4）分析了冰川物质平衡对降水、气温变化的敏感性及改进GSSHA模型在高寒小流域模拟中的误差及模型模拟不确定性。研究成果可为青藏高原典型高寒山区流域水文模拟提供重要参考依据。