Accurate crop evapotranspiration simulation is vital for reasonable irrigation planning. The two-step method for crop evapotranspiration estimation has been widely used for irrigation water demand management. However, in the two-step method, the crop coefficient (K_c) is typically taken as a constant in crop growth stages, which may result in a certain error in evapotranspiration estimation. It is of significance to estimate K_c accurately for effective water resources management. Based on three-year lysimeter experimental data collected from the Wudaogou Station for Hydrology and Water Resources, this study proposes a thermal-based K_c method for actual crop evapotranspiration estimation. The proposed thermal-based K_c method uses air temperature and soil heat flux as input variables, which could mainly characterise the thermal effect on crop growth from the atmosphere and soil. Results showed that the proposed method is effective in estimating K_c. The estimated K_c highly correlates with actual K_c values, which are derived from lysimeter observation, with correlation coefficient above 0.87 and Nash-Sutcliffe efficiency above 0.70. The proposed method could estimate K_c daily, which can be used to estimate crop evapotranspiration accurately.

准确的作物蒸散模拟对于合理的灌溉规划至关重要。作物蒸散量估算的两步法已广泛用于灌溉需水量管理。但是，在两步法中，作物系数（K _c）通常在作物生长阶段被视为常数，这可能导致蒸散估计存在一定的误差。准确估算Kc_对于有效的水资源管理具有重要意义。基于从五道沟水文水资源站收集的三年蒸渗仪实验数据，本研究提出了一种基于热力的K _c实际作物蒸散估计的方法。所提出的基于热的K _c方法以气温和土壤热通量作为输入变量，主要表征大气和土壤对作物生长的热效应。结果表明，所提出的方法在估计K _c方面是有效的。估计的K _c与实际K _c值高度相关，这些值来自蒸渗仪观察，相关系数高于 0.87，Nash-Sutcliffe 效率高于 0.70。所提出的方法可以每天估算K _c，可用于准确估算作物蒸散量。