鄂尔多斯盆地风沙滩地区裸土蒸发动力学研究

The shortage of water resources has become one of the most important bottlenecks for the development of industry and agriculture in the Ordos Basin. Moreover, the increasing water demand is a serious threat to ecosystems. Unproductive evaporation from groundwater through the soil constitutes the most important loss of water resources in this area. Evaporation rates are controlled by various factors, including atmospheric forcing, soil thermodynamics, the hydraulic properties of the soil, moisture transport in the vadose zone as well as groundwater dynamics. Moreover, the physical equations that describe these complex processes and their feedback mechanisms are highly non-linear and far from being fully understood. To optimize water resources management in arid regions an improved process understanding of soil evaporation is urgently required. In order to improve the current process understanding, an innovative combination of field and laboratory approaches that form the basis for state of the state-of the art modelling techniques is proposed. The project benefits from long time series of highly instrumented field-sites as well as well-equipped laboratories including lysimeters that allow to systematically assess evaporation processes under controlled conditions. These information provide the foundation to a process-based modelling approach jointly simulating water in its liquid and vapor phase, as well as heat. The numerical models not only allows to identify the controlling factors of evaporation for a range of groundwater- and atmospheric conditions, but also allow to assess the performance of the current approaches used to estimate evaporation rates in the field. The project therefore not only contributes to an increased process understanding, but also is of high relevance to the sustainable water resources management in an area where the competition for water for anthropogenic use and nature is imminent.

水资源短缺已成为制约鄂尔多斯盆地风沙滩地区工农业发展和生态环境保护等主要因素之一。强烈蒸发是该地区地下水资源最主要的天然排泄量之一，精确估算裸土蒸发对于提高当地水文和气候模式以及环境、农业及工程等领域的认识有着至关重要的作用。受大气、土壤热力、水力特性等复杂影响因素，加之包气带水分运移机理复杂及控制方程具有高度非线性等制约，对旱区深化蒸发动力学机制仍然十分薄弱。本项目以半干旱气候环境的鄂尔多斯盆地风沙滩为研究对象，综合利用室内物理模拟、野外原位试验与长期观测及数值模拟等技术手段，将大气-地表-包气带-地下水作为一个整体，揭示不同条件下裸土蒸发的影响因素及规律，评价裸土蒸发计算方法的适用性，揭示地表-地下水系统裸土蒸发机理，构建水汽热耦合动力学模型，甄别参数不确定性对计算蒸发量的影响，解析在小时-天-月-旬-年等多时间尺度蒸发量的变化规律，为研究区科学管理水资源提供理论依据。

项目聚焦鄂尔多斯风沙滩地区裸土蒸发动力学，综合利用室内物理模拟、野外原位试验与长期观测及数值模拟等技术手段，将大气-地表-包气带-地下水作为一个整体，从时间和空间两个维度开展研究，取得以下成果：（1） 分析了不同地下水位埋深条件下裸土蒸发规律，评价了裸土蒸发计算方法在不同地下水位埋深条件下的适用性，基于薄膜流理论，提出了干旱-半干旱区裸土蒸发计算公式；（2）构建了大气-地表-包气带-地下水系统的水汽热耦合模型，揭示不同气候条件下（干旱、半干旱、半湿润）、不同地下水水位和不同介质对水汽通量的影响，在半干旱地区，忽略温度导致高估了16.2%的蒸发量和低估了13.2%的地下水补给量；（3）研发了有限分析数值模拟技术，破解了有限分析法在非均质界面不连续的问题，在此基础上，研发了基于时间项和空间项局部解析解的有限分析数值模拟方法，丰富和完善了有限分析数值模拟方法；（4）揭示了鄂尔多斯风沙滩地区凝结水形成机制，讨论了凝结水影响因素，定量化了影响因素对凝结水的贡献率，揭示了凝结水对水量平衡的影响。（5）构建了大气-典型植被-包气带-地下水系统原位监测点，为鄂尔多斯风沙滩地区植被恢复提供数值支撑。上述研究结果被中国地质调查烟台海岸带地质调查中心应用。