冻土对寒区水文过程具有重要的调节作用,是寒区水循环研究的核心内容之一.在分布式水文模型中对土壤冻融过程进行显式表达,对探索寒区水循环的机理、定量研究寒区流域径流的时空变化十分重要.先在黑河上游八宝河流域对考虑了土壤冻融过程的分布式水文模型进行简单验证,然后分析土壤冻融对流域水文过程的影响.对考虑和不考虑土壤冻融的模型模拟结果进行对比,发现冻土对流域的产流方式和速度有很大的影响,主要表现为: 1)考虑冻土时,流域产流以壤中流为主,径流对降雨或融雪的响应速度较快,径流过程线变化较为剧烈,径流系数较高.冻土有效地阻碍了入渗过程,促进地表径流和壤中流的形成.壤中流发生的平均土壤深度冬季深,春季浅,年平均深度约为1.1 m; 2)在不考虑冻土时,土壤下渗能力强,地下水补给是考虑冻土时的3倍,流域产流方式以基流为主,径流对降雨或融雪的响应速度减缓,径流过程线较为平滑,夏季洪峰在时间上存在明显的延迟.即便在降水强度较大的夏天,流域内都不会产生地表产流,而且壤中流产流的平均土壤深度平稳地处于2.4 m左右.研究对从机理上认识土壤冻融对水文过程的影响有一定的帮助.
英文摘要:
Because of the regulating effect of frozen ground in infiltration and runoff generation,the effect of frozen ground is essential to understand the hydrological process in alpine regions. To quantitatively assess the changing trends of runoff owing to climate change and to understand the underlying mechanisms in the hydrological process in alpine regions,it is necessary to explicitly integrate the processes of ground freezing and thawing into traditional distributed hydrological models. In this paper,the physically based simultaneous heat and water frozen ground model is coupled into the geomorphologic-based distributed hydrological model. After a simple validation in the Baba River basin,a sub-basin in the upper reaches of the Heihe River,the model was used to analyze the influences of frozen ground on the runoff and discharge. The results show that the model appears to be acceptable and frozen ground has significant influences on the runoff generation. In the base model with a frozen ground module,subsurface runoff is dominated and the river runoff responses quickly to rainfall and snowmelt,which results in violent variation. In addition,notable surface runoff due to excess infiltration occurs at high elevations. When the frozen-ground module do not be considered,the simulated groundwater and base flow will increase 3 times. At the same time,the simulated hydrograph was much smoothened and flattened, with delay in the occurring time and attenuation in the summer flood peaks. The simulated average depth,at which the subsurface runoff takes place,is about 2.4 m,deeper than that of 1.1 m simulated with the base model. In spite of some existing limitations,this study is still useful because it provides a theoretical and quantitative understanding in the influences of frozen ground on cold hydrological processes.