在降水量<400毫米的干旱和半干旱地区,蒸散量(ET)约占降水量的80%,是流域的主要用水户。然而,近年来的植被绿化将通过影响根系中的土壤水分来增加ET并加剧该地区的干旱。植被变化是区域性和空间异质性的,因此,为了表征植被动态下的ET变化,有必要扩大ET模拟的空间尺度。然而,广泛使用的蒸散模拟模型,例如Shuttleworth-Wallace模型(SW模型),在反映垂直(即,土壤深度)和水平(即,植被动态)方向。在现场抽样的基础上,构建了结构方程模型(SEM),我们发现植被动态不仅直接影响蒸散,但也间接影响不同深度的土壤水分。在此基础上,我们定义了草地植被带的加权系数为0.85和0.15,林草散布区0.3、0.15、0.20、0.25、0.10,林地为0.20、0.55、0.25,分别,基于SEM结果。在不同的植被类型区域内定义了不同的土壤水分加权系数,改进的SW模型称为S-W-α。将仿真结果与实测数据进行比较,S-W-α将该区域的ET模拟精度提高了33.92%,并且改进的ET空间趋势可以响应植被的动态变化。用改进的S-W-α替换块式使用TOPMODEL和Muskingum-Cunge方法模式(BTOP模型)中的ET模块,结果表明,改进模型的仿真精度提高了25%,在费率期和验证期内,纳什都高于75%,实现了模型从点尺度到流域尺度的扩展。改进后的模型可为生态脆弱地区的蒸散模拟和生态系统健康管理提供技术支持。
In arid and semi-arid areas with <400 mm of precipitation, evapotranspiration (ET) accounts for about 80% of precipitation and is the main water consumer in the watershed. However, vegetation greening in recent years will increase ET and exacerbate the aridity of the area by affecting soil moisture in the root system. Vegetation changes are regional and spatially heterogeneous, therefore, in order to characterize ET changes under vegetation dynamics, it is necessary to expand the spatial scale of ET simulation. However, widely used evapotranspiration simulation models, such as the Shuttleworth-Wallace model (SW model), are deficient in reflecting the direct and indirect effects of vertical (i.e., soil depths) and horizontal (i.e., vegetation dynamics) directions. Based on field sampling and constructed structural equation model (SEM), we found that vegetation dynamics affect evapotranspiration not only directly, but also indirectly by affecting soil moisture at different depths. On this basis, we defined the weighting coefficients of 0.85 and 0.15 for grassland vegetation zones, 0.3, 0.15, 0.20, 0.25, 0.10 for forest-grass interspersed zones, and 0.20, 0.55, 0.25 for forested zones, respectively, based on the SEM results. Different soil moisture weighting coefficients were defined within different vegetation type zones and the improved SW model is called S-W-α. Comparing the simulation results with the measured data, S-W-α improved the ET simulation accuracy in this region by 33.92% and the improved ET spatial trend can respond to the dynamic changes of vegetation. Replacing the ET module in the Block-wise use of TOPMODEL and Muskingum-Cunge method mode (BTOP model) with the modified S-W-α, the results show that the simulation accuracy of the improved model is increased by 25%, and the Nash is higher than 75% for both the rate period and the validation period, which realizes the extension of the model from the point scale to the basin scale. The modified model may provide technical support for simulation of evapotranspiration and management of ecosystem health in ecologically fragile areas.