西北干旱区灌溉绿洲水分传输阻抗观测试验研究

Evapotranspiration of land surface is essentially a regulative process of various resistances to water transfer under certain environmental conditions. In the arid area of northwest china, there is still lack of observational and experimental studies of the water transfer resistances in the irrigated oases. In the present research proposal, a representative crop field of Linze oasis is chosen to carry out the observation and experiment in the arid area of northwest China. A comprehensive field study will be conducted of water transfer and related energy transfer processes in and above the crop canopy of the crop field. The soil and crop of the field is treated as two relative independent source/sink terms of water transfer. The variation and interaction will be studied of the bulk stomatal resistance of the canopy, bulk boundary layer resistance of the vegetative elements in the canopy, surface resistance of the soil, aerodynamic resistance between the soil surface and the canopy source height, and the aerodynamic resistance between canopy source height and reference level. The rational computation on the resistances will be formulated suitable to the arid and irrigated environment, and then the crop transpiration and soil evaporation of the field will be simulated and the computed resistances evaluated. The present study is aimed at improvement of the computation methods of plant transpiration and soil evaporation, revealing of the interrelationship among plant transpiration, crop growth, irrigation and soil evaporation, and inquiring into the relation of plant growth to water consumption and environmental factors. The present study is focused on the key problem of water transfer resistances to calculate the evaporation and transpiration of irrigated oases in the arid area, and will contribute to understanding the roles and influence factors of resistances in the processes of evaporation and transpiration during the plant growth season, to inquire into the mechanism of water transfer regulation.

陆地表层的蒸散发实质上是在一定环境条件下各阻抗对土壤和植物向大气水分传输的调节过程。在我国西北干旱区，尚缺乏灌溉绿洲水分传输阻抗的观测试验研究。本项目拟选择西北干旱区临泽绿洲代表性灌溉农田为观测试验场，通过土壤和植物向大气水分传输及其伴随的能量传输等综合观测试验，研究土壤和植物冠层两个相对独立的源/汇与大气间水分传输过程中的冠层总气孔阻抗、冠层与邻近空气的边界层阻抗、土壤表面阻抗、土表到冠层以及冠层到参考高度空气动力学阻抗的变化规律与相互关系，提出适用于该特殊环境条件下各阻抗项的合理计算方法，对绿洲农田植物蒸腾和土壤蒸发过程进行模拟和验证，揭示干旱区灌溉绿洲农田植物蒸腾和土壤蒸发之间的关系及其植物与环境控制机理。本项目抓住了干旱区绿洲蒸散发计算中水分传输阻抗这个关键问题，特色鲜明；在认识干旱区灌溉绿洲作物不同生育期各水分传输阻抗对土壤蒸发和植物蒸腾过程的调控效应方面有创新。

本项目连读四年（2013-2016）对西北干旱区河西走廊典型灌溉绿洲核心区域代表性下垫面-灌溉玉米农田的微气象、湍流通量、植物蒸腾、土壤蒸发等关键水热传输过程进行综合观测试验，全面分析了灌溉绿洲下垫面（土壤和植物）与大气间辐射传输、水分输送和能量交换过程，深入研究了干旱区灌溉绿洲下垫面与大气间各项水汽输送阻抗的合理计算方法，模拟了灌溉绿洲下垫面土壤-大气、土壤-植物、植物-大气界面水分输送的耦合过程。本项目严格按照研究计划，顺利实施了所有研究内容，高质量完成了预期目标。主要成果包括：①分析了植物生长过程对灌溉绿洲下垫面植被冠层内外风速、温度和湿度垂直廓线分布特征的调节作用；②提出了适用于干旱区灌溉绿洲的各项空气动力学阻抗和表面阻抗的合理计算方法，量化了各项阻抗之间交互影响效应及其对土壤-植物-大气系统水热交换调控的相对贡献；③阐明了由植物生长过程对灌溉绿洲下垫面辐射平衡、能量平衡和水热再分配过程的影响及其相互作用机理；④确定了植物蒸腾过程对环境驱动力响应的尺度效应及其阈值，为构建不同尺度蒸散发过程估算模型提供了关键参数；⑤基于陆地表层与大气间水热交换的双源模型（视土壤和植物两个相对独立的源/汇），结合各水分传输阻抗的合理参数化方案，模拟并确定了灌溉绿洲水分平衡季节变化规律及其各组分之间的相互关系，阐明了各项水汽输送阻抗在灌溉绿洲下垫面与大气间水热交换过程的调控作用；⑥发现了植被同时吸收了冠层上方的辐射和来自土壤的感热通量，为认识下垫面植物-土壤系统内复杂的水热交换及其耦合过程与相互作用机理提供了关键理论依据。通过本项目的实施，提升了我们对干旱区灌溉绿洲主要水分平衡分量—蒸散发过程的估算能力，增进了我们对西北干旱区灌溉绿洲这一特殊环境条件下水分耗散过程与水热平衡过程的相互作用及其植物与环境调控机理的认识，为西北干旱区灌溉绿洲水资源管理和节水型社会建设提供了基础数据和理论支撑。