山区太阳辐射对水热过程影响的敏感性分析

A Sensitivity Analysis of Effect of Solar Radiation on Heat and Water Process in Mountainous Regions——a Case Study in the Upper Reaches of the Heihe River

山区短波辐射的空间异质性非常强,地形的遮蔽影响在山区能水循环模拟研究中不容忽视.改进了SHAW模型和SHAWDHM模型的辐射模块,使之能考虑地形的遮蔽作用对山区辐射平衡及其空间分布的影响,并在单点和流域尺度进行数值模拟实验,对比分析山区辐射过程对流域能水循环和径流的影响.结果表明,因地形的遮蔽作用,地表接收的太阳直射辐射可减少25%左右,模型模拟的土壤温度和蒸散发量分别降低约0.5℃和20%.考虑山区辐射过程后,模型模拟的春季融雪和夏季蒸散发均有所减缓,导致春季融雪径流降低和夏季径流增加.与观测径流对比发现,考虑山区辐射过程后,模型对径流量的模拟精度有所提高,逐时径流量的纳什效率系数由0.677提高到0.711,径流量的观测值与模拟值间的相关系数由0.835提高到0.851.

The spatial distribution of solar radiation in mountainous regions is strongly heterogeneous.The shadowing effect of rugged relief is not allowed to be ignored in modeling the energy and water balance in mountainous regions.The solar radiation on a slope in rugged relief is affected by the slope,aspect,self-shading and shadow cast from surrounding topography.They change the proportion of direct and diffuse radiations in the solar global radiation and become more sensitive in energy and water cycles as the topography complexity increases.In this paper,the solar radiation modules of SHAW and SHAWDHM are modified in order to consider the topographic effects on the energy balance based on the digital elevation model.Point and distributed numerical simulations are conducted with the modified and original models,respectively.Results by the improved model show that in regions most affected by shadow,the direct radiation reaching the slopes will decrease by 25%,and the simulated soil temperatures and evapotranspiration will reduce by 0.5 ℃ and 20%,respectively.Considering the topographic effects on energy and water cycles and then on solar radiation,snowmelt in spring and evapotranspiration in summer will significantly reduce,as a result,discharge in the snowmelt period will decrease and discharge in summer will increase.The modified model is able to enhance the accuracy of runoff simulation.