流域蒸散发研究是明晰流域水循环机理，支撑流域水资源优化配置的基础。但是，现有的流域蒸散发理论尚不能全面揭示不同时间和空间尺度上的蒸散发变化规律。本论文的主要研究目的是：从理论上重新推导流域水热耦合平衡方程，并探讨将其用于估计流域实际蒸散发量和预测气候变化对流域蒸散发的影响。Budyko假设指出，多年尺度上流域实际蒸散发量E的控制性因素是降水量P和潜在蒸散发量E0，三者之间存在一定的函数关系。基于这一思想，本文提出了描述多年平均流域水热耦合平衡关系的偏微分方程，并从理论上证明该方程的解含有一个参数；由流域水文过程的基本原理给出偏微分方程的边界条件，结合量纲分析的Buckingham Pi定理，求得偏微分方程的解析解，即流域多年平均水热耦合平衡方程。考虑土壤初始含水量的影响，定义任意时段可利用水量的概念，推导得到任意时间尺度的水热耦合平衡方程，以此将适用于长时间尺度的Budyko假设和适用于短时间尺度的Penman假设从理论上进行了统一。采用通量实验站的观测数据，在田间尺度上验证了水热耦合平衡方程在月、旬和日时间尺度上的适用性。然后将方程用于模拟叶尔羌绿洲的月耗水过程，并对比干旱区平原绿洲四水转化模型的模拟结果，一定程度上说明了方程在区域尺度上的适用性，指出方程中的参数与区域综合的作物生长状况相关，这为作为水资源规划基础的耗水分析提供了工具手段。定量评估气候变化对水文循环的影响时，E0作为与大气状态相关的物理量，既是E变化的原因，也是E变化的结果，即E和E0同为未知量，故只依靠水热耦合平衡方程无法求解，为此引入Bouchet假设，建立定量评估E对气候变化响应的模型。对我国最近50年间的气象观测数据进行的分析表明，气象要素的变化具有地区差异，温室气体和气溶胶浓度的增加可能是气候变化的原因。利用模型进行的分析结果表明，不同地区实际蒸散发对气候要素变化的敏感性不同，实际蒸散发的变化趋势和起主导作用的气候要素也各不相同。
In the catchment scale, study on evapotranspiration is the basis for understanding hydrological cycle and for optimal allocation of water resources. But present theories on regional evapotranspiration have limitations to fully understand the spatial and temporal variability of evapotranspiration and for accurate estimating the actual evapotranspiration. Main objectives of present study are to derive the coupled water-energy balance equation based on existing evapotranspiration theories, and exploring its applicability for estimating the actual evapotranspiration and predicting the change trend of actual evapotranspiration due to climate change.Budyko hypothesis indicates that actual evapotranspiration in a catchment was dominated by precipitation and potential evapotranspiration over a long time scale, and the relationship of these three variables can be expressed as a function. Following this hypothesis, a set of partial differential equations was presented to describe the coupled water-energy balance in a catchment. Solution to these equations has only a parameter if the solution exists. Based on the hydrologic principle, the boundary conditions were given for the partial differential equations. Using the Buckingham Pi Theorem, the analytical solution was obtained, i.e. mean annual coupled water-energy balance equation. Considering the effect of soil moisture on actual evapotranspiration, this thesis also derived the coupled water-energy balance equation at any arbitrary time scale, and the equation was the same as the Budyko hypothesis at long-term time scale and the same as the Penman hypothesis at short time scale. Based on the flux observation at experiment stations in the Asia Monsoon region, the coupled water-energy balance equation was validated over different time scales, i.e., from a monthly time scale to daily time scale. The equation was used to calculate the monthly actual evapotranspiration of the Yerqiang Oasis, and the result was compared with that estimated by the oasis runoff-evapotranspiration model. It showed that the equation was usable for estimating actual evapotranspiration at regional scale. It offers a useful tool for the water consumption analysis for the water resources allocation program. The parameter of the equation has been found to have a positive correlation with the regional integral condition of vegetation.When evaluating the response of actual evapotranspiration (E) to climate change, potential evapotranspiration, a function of atmosphere state, it is both the result of and the cause for E. Therefore, the coupled water-energy balance equation can’t estimate E independently. Based on Bouchet and Budyko hypotheses, a model for evaluating hydrologic response to the changes of climatic factors was established. Using the meteorological data during the past 50 years, it was been found that changes in climatic factors have significant regional variability. The increase in greenhouse gases and aerosols may be responsible for climate change. Based on the results estimated by the model, I analyzed the regional variability in the sensitivity of actual evapotranspiration to climatic factors, as well as the trend in actual evapotranspiration and the dominative climatic factors in China.
