全球气候变化背景下，草原灌丛化已经成为全球范围普遍发生的现象。本论文以内蒙古灌丛化草原为研究对象，通过分析地表能量变化，并结合双源模型与牛顿-拉夫逊迭代算法，模拟群落蒸散发及其组分。在此基础上，通过情景化设计，应用该模型量化灌丛及草地对生态系统的蒸散贡献率，探讨了灌丛化对蒸散发及其组分的影响，并研究了灌丛化过程蒸散发的主要影响因子。主要研究结果如下：（1）利用波文比能量平衡法对双源模型模拟结果进行了验证，潜热和显热的相关性分析结果表明双源模型对于灌丛化草原蒸散发的模拟较为准确。日尺度上，利用野外实测温度与模型模拟温度进行比较，结果显示双源模型对于植被和土壤温度的模拟都有较高的准确性。此外，本论文通过敏感性分析评估了模型性能，结果表明叶片气孔阻抗最小值（rst_min）、叶面积指数（LAI）和温度（Ta）为主要敏感因子。（2）日时间和季节时间尺度上，植被的冠层导度都是蒸散比值（T/ET）的主要控制因子。日尺度上，土壤含水量和植被叶面积指数为定值时，太阳短波辐射为灌丛化草原植被蒸散比值（T/ET）更为直接的的影响因子；季节尺度上，叶面积指数和土壤含水量为蒸散比值（T/ET）更为直接的影响因子。（3）通过模型的情景模拟（全灌木覆盖或全草本覆盖）将灌丛化草原中灌丛和草地的蒸散进行了分离。结果表明：生长季期间，灌丛斑块蒸散发日平均速率高于草地斑块，分别为2.80 mm/d和2.52 mm/d。由于灌丛盖度约为15.35 %，研究区内灌丛斑块对群落蒸腾的贡献率明显低于草地斑块，为20.06±7.09 %。大降雨事件后，草地斑块和灌丛斑块的蒸散比值（T/ET）明显升高，分别达到了0.46和0.70，其中草地斑块蒸散比值的变化更为显著，而灌丛斑块的响应时间较草地斑块更长，响应时间持续至少2天。其可能原因为草地斑块中草本植物根系主要密集分布在表层土壤，因此其水分补给较为迅速，草地斑块对降雨的利用更为高效。灌丛斑块中小叶锦鸡儿根系较深较发达，降雨对深层土壤的水分补给需要一定的响应时间，因此灌丛斑块对降雨的响应滞后于草地斑块。随着7月份降雨量增加伴随的土壤含水量的上升使得草地斑块对群落蒸腾贡献达到了峰值87.08±1.12 %。水分充足时期，草地斑块对群落蒸腾贡献优势更加明显，表明草地较灌丛蒸散耗水更加快速，但有关其内在机理有待进一步研究。此外草原灌丛化过程对植被蒸散发组分的影响更为直接的原因为叶面积指数的改变。季节性降雨和降雨特征在一定程度上改变了灌丛化草原的蒸散发组分，并使得灌丛斑块的水分利用情况区别于草地斑块的水分利用情况。

Under the background of global climate change, shrub encroachment into grassland has been a global phenomenon. This paper combined two-sources model and Newton–Raphson (NR) iteration scheme to simulate the surface energy balance and the evapotranspiration partition of shrub-encroached grassland in Inner Mongolia. In addition, with the model designed, the contribution of shrub to local ecosystem can be aquired. Through these data analysis, the influence of shrub encroachment to grassland can be quantified and the influential factors of evapotranspiration partition in shrub-encroached grassland can be explained and described. This study gave a deep understanding of eco-hydrological effects on shrub encroachment and its response to climate change, which provided important scientific significance and reference value. In the different scales, Bowen ratio energy balance method was applied to verify the results made by two-source model. The correlation analysis of latent heat and sensible heat illustrated that the two-source model was feasible for simulating evapotranspiration of shrub-encroached grassland. In the daily scale, the simulated temperature values were compared to the field measured values and they matched each other well. Sensitivity analysis was applied to test model performance, and minimum of leaf stomatal resistance (rst_min), leaf index (LAI) and air temperature (Ta) were the most influential factors. No matter in the diurnal scale or the seasonal scale, canopy conductance was the main controlling factor. In diurnal scale short wave solar radiation was the direct influential factor to the evapotranspiration ratio (T/ET) of shrub grassland when the soil water content and leaf area index (LAI) were constants, while in seasonal scale leaf area index (LAI) and soil water content were the direct influential factors.Model was applied to evapotranspiration partition of shrub patches and herb patches. Transpiration rate of shrub patches was slightly lower than herb patches’, they were 2.80 mm/d and 2.52 mm/d, respectively. Since the cover of shrub patches was 15.35 %, the shrub patches made less contribution to vegetation transpiration than herb patches (20.06 %). After a heavy rainfall event, the evapotranspiration ratio (T/ET) of shrub patches and herb patches increased significantly, reaching 0.46 and 0.70, respectively. Herb patches gained more obvious increase in the evapotranspiration ratio, while shrub patches needed more time to response to the rainfall event for two days at least. The possible reasons were that herb root distribution mainly concentrated in surface soil where the water supplied more rapid than deep soil. Therefore herbs could make use of rainfall more efficiently. On the contrast, the shrub roots distributed in deeper soil, where the supply of water needed time. So it needed more time for shrub to response to rainfall. Differences of root distribution led to different response characteristics of shrub and herbs to rainfall events. With the synchronously increasing of soil moisture and rainfall in July, the transpiration value reached the peak 87.08 %, suggesting that seasonal rainfall made a certain impact on evapotranspiration components of shrub-encroached grassland and strengthen the advantage of herbs’ contribution. In addition, the results of correlation analysis showed that leaf area index (LAI) was a more direct factor of shrub encroached effecting on evapotranspiration components, reaching the 0.01 level of significance related. And rainfall characteristics widened the difference of contribution of shrub and herbs to ecosystem evapotranspiration.