北方典型农田水热传输过程与作物生长的耦合机理及其模拟

The agricultural water use efficiency in China is low. One of the fundamental research contents closely related to improve the water use efficiency is understanding the variations in evapotranspiration over croplands and the crop yield. Evapotranspiration and the formation of crop yield are closely related. Their underlying processes are the interactions between water-energy transfer and crop growth. However, the coupling mechanism between them is still poorly understood. The project selects the plain area of the Haihe Basin as the study area and conducts the ecohydrological observations over a typical cropland (wheat and maize in rotation) in this area. Particularly, evapotranspiration and its relevant meteorological, crop physiological, and ecological factors at both canopy and leaf scales are observed. Based on these observations, the interactions among evapotranspiration, energy transfer, and crop physiological and ecological characteristics are explored, which is used to propose a method of estimating canopy-scale evapotranspiration based on leaf photosynthesis. Based on the typical observation and the canopy-scale evapotranspiration estimation method, the project is to propose a method of coupling the simulations of water-energy transfer and crop growth, and then to develop a new agricultural ecohydrological model referring to the existing groundwater model, water-energy transfer model, and distributed hydrological model. Given the long-term hydro-meteorological data and remote sensing data, the project is to conduct a simulation of long-term variations in water cycle, to particularly analyze the reason of the variation in evapotranspiration and the variations in crop yield and irrigation water demand. The resulting conclusions can be used for a scientific support for improving the agricultural water use efficiency.

我国农业水资源利用效率较低，与提高水资源利用效率密切相关的基础研究内容之一为掌握农田蒸散发和作物产量的变化规律。蒸散发与作物产量的形成过程密切相关，其本质为水热传输过程与作物生长的相互作用；然而，二者的耦合机理仍不明确。本项目以海河流域平原区为研究区域，开展典型农田（小麦和玉米轮种制）生态水文观测，重点为冠层和叶片尺度上蒸腾量及相关气象、作物生理生态因子的观测。通过观测，研究农田蒸散发与能量传输、作物生理生态特征的相互关系，以此揭示农田蒸散发的内在机理，提出基于光合作用的农田蒸散发计算方法。在此基础上，提出水热传输过程与作物生长的耦合模拟方法，参考已有地下水模型、水热传输模型以及分布式水文模型，开发新的农田生态水文模型。在长系列水文气象和遥感数据的支撑下，开展农田水循环过程长期变化的数值模拟，重点分析农田蒸散发演变的原因以及作物产量和灌溉需水的变化，为提高农业水资源利用效率提供科学支撑

本项目以海河流域平原区为研究区域，开展了典型农田（小麦和玉米轮种制）生态水文观测，观测重点为冠层尺度上蒸散发、光合作用、土壤呼吸及相关气象、作物生理生态因子。基于数据分析，掌握了冠层蒸散发、光合作用速率、冠层导度以及土壤呼吸的季节变化规律及其主控因子。结果表明，作物生长是冠层蒸散发、光合作用速率以及冠层导度的主要影响因素，土壤呼吸中的异养呼吸主要受土壤温度和水分的影响，而其中的自养呼吸还受作物生长的影响。基于实测水分、能量和碳通量的观测数据，本项目研究了作物生长过程与水分、能量传输过程的耦合参数化方法，开发了耦合作物动态生长和水热传输过程的农田生态水文模型。实测资料验证表明，该模型能够用于预测未来气候变化及灌溉量变化条件下灌区蒸散发以及粮食产量的响应。以海河流域平原区为研究区域，在长系列气象和遥感数据的支撑下，采用生态水文模型模拟了过去30年来该地区蒸散发的时空变化过程，并分析了蒸散发变化趋势的主要驱动因素，表明农田灌溉是蒸散发呈增加趋势的主要原因。本研究还揭示出灌溉模拟在生态水文模型中的重要性和不确定性，以及由此引起的农田耗水模拟的不确定性。