效率链框架下黄土高原流域蒸散与下垫面植被变化的耦合过程研究

By expanding the idea of cropland water use efficiency chain to the situation at watershed scale, the Kuye River watershed on the northern Loess Plateau and the Jinghe watershed on the southern are selected in consideration of the water-energy-carbon interactions. The research project is proposed with the specific objectives of analyzing the links from water supply, evapotranspiration, and transpiration to vegetation net primary productivity (NPP) and their ratios, forming the framework of water use efficiency chain at watershed scale, building the watershed water-carbon coupling function with the corresponding boundary conditions of limiting idea and investigating the coupling process and characteristics of watershed evapotranspiration and the underlying surface vegetation change. Combining the analysis of meteorological, hydrological and remote sensing data at watershed scale with the water carbon flux observed by using eddy covariance and supplementary irrigation experiment at field scale, the project is designed to conduct the coupled water-energy-carbon research at various space-time scales and extend the range of water supply in a certain region. The main contents of the project are 1) spatial and temporal distribution characteristics of watershed water balance based on the Budyko Hypothesis and the complementary relationship between actual evapotranspiration and potential evapotranspiration, 2) attribution analysis on the coupling process of watershed evapotranspiration and the underlying surface vegetation change, 3) water balance elements performance and water-carbon related features at different spatial scales and 4) watershed water-carbon coupling function and its analysis within the framework of water use efficiency chain. The project is expected to provide a technological support for reasonable use of regional water resources and development in agricultural production and ecological construction from the perspectives of precipitation controlled evapotranspiration and water-carbon relevance in non-humid regions.

把农田水分利用效率链思想扩展到流域尺度，考虑水热碳交互影响，选取黄土高原北部的窟野河流域和南部的泾河流域，分析从流域供水量、蒸散量、蒸腾量到植被净初级生产力间的若干环节及其比率，形成流域尺度水分利用效率链框架，并以相应的极限思想为边界条件，构建流域水碳耦合函数，研究流域蒸散与下垫面植被变化的耦合过程与特征。项目结合流域尺度上气象、水文及遥感数据分析，流域内农田尺度上基于涡度相关技术的水碳通量观测与补充灌溉试验，实现时空尺度变化与局地水分供应幅度扩展相结合的水热碳耦合研究。主要研究内容为，基于Budyko假设与蒸发互补关系的流域水量平衡及其时空分布，流域蒸散与下垫面植被变化耦合过程及其归因分析，尺度变化条件下水量平衡要素及水碳关联表现，效率链框架下流域水碳耦合函数及其解析特征。期望从非湿润地区降水主导蒸散与水碳耦合角度上，为区域水资源合理利用和农业生产及生态建设发展提供科技支撑。

地表蒸散与植被的关系是生态水文学的核心问题之一。本项目按照计划书以黄土高原为主要范围开展工作，在效率链框架下研究流域蒸散与下垫面植被变化的耦合过程。基于Budyko-Fu模型分析流域尺度水量平衡年际过程，给出了由植被覆盖度与气候季节性指数表达的控制参数的半经验计算公式；进一步分析不同时间尺度下影响控制参数的因子间的关联性及其对蒸散估算的影响，发现在长时间多年尺度上（30年），植被覆盖度与气候季节性指数及地形起伏度都呈显著相关，控制参数的函数构建上需要考虑这些因子间的多重共线性问题。在归因分析方面，把全微分方法应用到空间变化上，定量评估了气象要素对黄土高原潜在蒸散随空间距离变化的贡献量。基于长武野外站三个高度上水热通量观测数据，对广义非线性平流干旱模型（GNAA）进行了验证和应用；分析得到的模型参数值与以往用不同试验手段测定的或者有物理基础的参数值都在同一范围之内; 从2m到32m，由GNAA方法计算得到的蒸发值与对应的观测值之间的相关程度逐渐增加; GNAA模型的进一步推广应用需要采取其通式形式，对参数c由实测数据给予标定,其下限为-1，上限可大于2。在水分供应与生产力关系方面，黄土塬区农田尺度上冬小麦产量随底墒线性增加，产量与耗水量之间的关系可由Logistic曲线描述；由7年田间试验数据解析了春玉米水分利用效率链及其对地膜覆盖的响应特征，地膜覆盖使WUE增加了22.5%，使蒸散量占土壤贮水的比率增加了3.9%. 结合Budyko假设的边界条件，把流域水分供应与植被生产力形成相关联，初步就流域尺度水碳耦合关系进行了分析，给出了其数学表达。在该项目的支持下目前发表论文20篇，其中中科院一区论文7篇（均标注该项目编号）。项目执行期间，培养研究生12名，其中毕业获博士学位4名、硕士学位4名。