基于模块化建模方法的寒区水文过程模拟——在中国西北寒区的应用

中国西北高山、 高原广泛分布着冻土和积雪, 春季融雪和冻土融化是该地区重要的水文过程.基于模块化的寒区水文建模环境CRHM, 根据流域水文过程特征和观测数据约束, 选取描述不同寒区子水文过程的模块构建寒区水文模型, 并基于长期观测的两个典型寒区小流域来验证模块化的寒区水文模型.在冰沟流域, 主要模拟雪的积累/消融、 雪的升华、 融雪下渗和融雪径流过程. 结果显示: 冰沟流域积雪升华占降雪量(145.5 cm)的48%, 其中风吹雪引起的升华损失量(35 cm)占积雪升华(69 cm)的一半, 风速和辐射引起的积雪升华是该地区积雪物质平衡的重要组成; 构建的寒区水文模型可以再现春季积雪消融引起的径流过程.在左冒孔冻土流域, 主要模拟冻土下渗过程、 冻土坡面产流过程和土壤冻融对径流的影响. 结果显示: 构建的寒区水文模型可以捕捉到春季主要的冻土融化径流过程.两个流域的验证结果揭示: 模块化的建模方法在搭建模型结构的时候减少了模型的不确定性, 所以在未经率定的情况下, 具有在无资料和资料缺少地区模拟寒区水文要素和水文过程的能力.

Simulating the Cold Regions Hydrological Processes in Northwest China with Modular Modeling Method

The permafrost, seasonally frozen soil and snow cover are widely distributed in Northwest China. Spring snowmelt and frozen-soil thaw are normally the most important hydrological events in the region. However, modeling cold regions hydrological processes is full of problems because of lack of data in watershed scale. The Cold Regions Hydrological Model (CRHM) platform, a flexible object-oriented modeling system, was devised to solve this problem with connecting modules into model by problem objectives, scale of application and data constraints. In this study, two watersheds were chosen to validate the CRHM. One is the Binggou watershed, which is an experimental area for researching snow accumulation and ablation processes and researching the influence of snow ablation on runoff. Another one is Zuomaokong watershed, which is an experimental area for understanding the effects of soil freezing-thawing on runoff process. For Binggou watershed, the cold regions hydrological model was created within CRHM to simulate the contribution of sublimation to alpine snow mass balance and snowmelt runoff process. Comparison of simulated snow depth with observations during October 30, 2007 to May 6, 2008 shows that the snow accumulation/ablation processes can be simulated much better with a physically based snowmelt model, which includes the layered, hourly time step, energy balance snowpack ablation (Snobal CRHM) module and blowing snow module (pbsmSnobal), rather than a temperature index snowmelt model. Further comparison of simulated results through switch on/off different process modules reveals that the sublimation loss could reach to about 69 cm in the alpine region of Binggou basin, accounting for 48 % of the total snowfall (145.5 cm), and the half sublimation loss is attributed to snow drifting (about 35 cm). The conclusion could be drawn that snow sublimation loss is vital for accurately calculating snow ablation and snow drifting sublimation loss is significant in the alpine region of Binggou basin. Meanwhile, the model is able to well reproduce the measured streamflow without calibration, with RMSEof 0.52 m³·s^-1and NSEvalues of 0.64. For Zuomaokong permafrost watershed, the cold regions hydrological model is created within CRHM to simulate the influence of soil freezing-thawing process on runoff. Comparison of simulated results with observation shows that model including module for handling frozen soil infiltration can capture the main runoff processes, especially that in frozen-soil thawing period in spring. The RMSEand NSEvalues between simulated and observed runoffs are 0.31 m³·s^-1and 0.67, respectively. Overall, the validated results for the two watersheds show that CRHM is capable of simulating various elements of the cold regions hydrological cycle in Northwest China without calibration. This is encouraging for the model able to predict the hydrological processes in ungauged basins.