水沙物理模型CASC2D-SED的DEM尺度效应发生机制

DEM分辨率对分布式水沙过程模拟具有重要影响,然而,产生影响的内部机制尚不明确。改进水沙物理模型CASC2D-SED的结构,将坡度由DEM在模型内部直接提取改为由模块单独计算,并将坡度设计为模型的独立输入参数,通过单独改变坡度参数来研究坡度对水沙模拟DEM尺度效应的影响。基于改进的CASC2D-SED模型,以内蒙古准格尔旗沙圪堵镇附近的一个小流域为研究对象,以无人机航测的1m分辨率DEM数据、野外实测与室内实验获得的土壤特性数据、土地利用数据和降雨数据为基础,采用3种水沙模拟方案进行多象元尺度的水沙过程模拟,进而探索水沙过程模拟的DEM尺度效应及发生机制。研究表明:⑴在4~20m GRID分辨率区间模拟的径流量位于323.18m3和411.43m3之间,波动不大;⑵2~20m GRID分辨率区间内,模拟的侵蚀流量在3.43m3和65.61m3间变化,波动很大;(3)坡度和径流路径是水文过程模拟DEM尺度效应的两个对立影响因子,是水文过程模拟DEM尺度效应不明显的主要原因;⑷DEM尺度效应对侵蚀输沙具有重要影响,地形坡度是侵蚀输沙DEM尺度效应的主要控制因子;⑸地形坡度随DEM分辨率降低而发生的空间上的波动变化是侵蚀输沙量随DEM分辨率降低而波动变化的原因。

Mechanism of DEM Scale Effect Based on Runoff and Sediment Model CASC2D-SED

DEM resolution has important effects on process simulation of runoff and sediment. However, the internal mechanism ofthem are unclear. Through calculating the slope separately by the module instead of the gradient extraction directly by the DEM ininternal model and slope design as independent input parameters for the model, the runoff and sediment CASC2D-SED was improved.We researched the slope contribution to DEM scale effect of runoff and sediment modeling by changing the parameters ofslope alone. The small watershed, near Shagedu Town of Jungar Banner in Inner Mongolia, as the research object, we simulated theprocess of runoff and sediment using three kinds of schemes in different grid cell size taking UAV one resolution DEM data, soilcharacteristics data obtained by field survey and experiment, land use data, rainfall data, runoff and sediment data as basic inputparameter based on the improved CASC2D-SED model. The results show that (1) the simulated runoff lies between 323.18m3 and411.43m3, and fluctuation is not big within the range of 4 to 20m grid resolution; (2) the simulated erosion flow changes between3.43m3 and 65.61m3 within the range of 2 to 20m grid resolution, and fluctuation is big; (3) the slope and runoff path are two opposingfactors on DEM scale effect of hydrological process simulation and it is the main cause of DEM scale effect on hydrologicalprocess simulation without obvious changes; (4) DEM scale effect has important effects on erosion sediment, and terrain slope is themain control factor on DEM scale effect of erosion sediment; (5) the spatial variation of terrain slope changing result from DEMresolution is the main reason of the change of eroded sediment discharge in volatility.