基于水平衡关系的水文要素图化方法研究

Mapping large scale regional variations in hydrological behavior has a long tradition in hydrology as well as in other geosciences like meteorology, climatology and geography. The main hydrometerological processes (rainfall, evapotranspiration, temperature etc.) when observed at the land surface develop in a three-dimensional space - the two geographical coordinates (x, y) and time t. The variation of these variables across space is described as contour maps in classical works, i.e. they are space-filling phenomena and allow straightforward interpolation. River discharge (surface runoff), on the other hand, is formed in a two- dimensional space - the distance along a river (related to the point with area A in a basin) and time t . This relationship to the area (and not the (x, y) coordinates) explains why the variation of runoff characteristics across space, determined from discharge measurements, cannot be plotted as simply as hydrometerological variables. Neither is it a space-filling phenomenon. .This proposal aims at combining the water balance constraint and stochastic approach for producing choropleth maps of water resourses under changing enviorment. To avoid the uncertainty in hydrological model, this study is just based on data. From singal component (runoff) to multiple components (precipitation, evaporation and runoff), the stochastic approach based on water balance is built. This proved the possibility of combining the geo-statistic and the hydrology. A technique is presented for a joint interpolation of water balance components that considers estimated or observed values with their a-priori uncertainty and yields balanced interpolated values, which respect the water conservation at all levels within the hydrographical network. The approach allows building a consistent water balance pattern, where both the observed values and water balance constraints are given full recognition. The framework presented has strong similarities with assimilation, as it is understood in meteorology (i.e. tuning a model to observed data). It proved to be an excellent diagnostic tool for data in an exploratory phase when investigating patterns of variability. Stochastic interpolation using data from the meteorological and hydrological networks were used to produce a set of prior digital maps of precipitation, actual evapotranspiration and runoff..The new theory is then used to analyze the water resources of Huai River basin in changing environment. It would be of great value for ensuring water supply in this densely populated part of China to get insight in the water cycle in the basin and follow its development in time. The results are meant to be used in a larger project on Water Atlas of China, as a next step of research.

由于气候变化和高强度人类活动的影响导致流域下垫面变化的复杂性，跨时空尺度水文图化（Mapping）的研究已成为当前国际水文科学研究的热点前沿问题，其关键科学问题是构建基于水平衡理论的径流空间插值方法。本项目将流域水循环及水量平衡物理制约关系与水文要素的空间插值方法相结合，提出流域尺度下径流空间插值算法，建立径流空间插值不确定性评价体系；通过将垂向水量平衡约束条件加入到空间插值方法中，建立降雨、蒸发、径流三者之间的相关关系，提出一种基于水循环多要素联合空间插值的水文图化方法，并将其应用于我国典型流域，分析变化环境下水文要素的时空分异特征，为揭示变化环境下流域水资源时空格局演变提供新方法。该项研究对推动水文学的发展和流域水资源管理有重要的意义。

长期以来，水文地理要素的时空变化与分异特性主要使用等值线图等分析方法，存在着将不同尺度水文物理过程变化与时空分异统计特性联系与结合的问题。由于气候变化和高强度人类活动的影响导致流域下垫面变化的复杂性，跨越不同时空尺度水文要素时空分异性及其图化（Mapping）问题的研究已成为当前国际地理水文科学研究的热点前沿。主要面临的科学问题与难点是如何将流域水循环要素变化的物理过程与不同尺度水文要素时空分异的随机特性相结合，迫切需要探讨基于水平衡关系的水文要素时空分异图化方法研究及其应用。. 本研究将流域水循环及水量平衡物理制约关系与地理分异的空间插值方法相结合，研究变化环境下水资源的时空分异特征，发展针对水文要素的空间插值图化方法，以避免因水文模拟环节增加而带来的不确定性。研究首先建立了适合中国大尺度流域特征的水文随机方法，并在大流域上进行了插值试验，并证明了该方法的可行性。将天然径流的“点”信息进行空间插值可以得到两种描述径流量的空间分布图，反映沿河道径流量的变化。结果显示，在有限的观测数据条件下，通过控制DEM、站点坐标、数字化河网等空间信息的输入精度，在水量平衡的约束下，利用水文随机方法可以在大尺度流域内得到径流的空间分布特征，尤其是在进行汇流之后可以得到精度较高的河道内径流分布结果，在整个研究区范围内给出径流插值误差的定量化描述。在此基础上，研究提出了基于水平衡关系的多要素联合图化方法，通过在降雨、蒸发、径流三者空间插值结果之间建立相关关系，解决了以往水文三要素模拟过程中各自独立的问题，成功的将垂向水量平衡约束条件加入空间插值方法，实现了水文过程三要素的联合图化。联合插值方法考虑到了插值误差和数据误差，并产生新的纠正后插值结果，该结果可以保证在所有水文地理层次上的水量守恒。水平衡纠正方程的主要元素是原始插值结果和总体水量平衡偏差，纠正过程需要精确地计算各个要素如何分担总体平衡误差。该方法对各个水平衡要素空间插值误差之间的关系非常敏感，在给每个要素单独增加10% 的系统误差后, 纠正程序会得到与原始情景差异显著的结果。联合图化方法可以给出数据系统误差和随机误差的数量级，对数据资料的质量进行评估。