我国半干旱气候下参考作物蒸散试验及其计算方法和参数研究

Accurate calculation of reference crop evapotranspiration (ET0) is the key to improve estimation accuracy of crop water requirement, and it is thus an essential problem to be resolved in water resource management. However, scarcity of the measured ET0 and insufficient evidence for choosing the approriate input driving parameters and model parameters in the ET0 formula often lead to uncertainty in the etsimated crop water requirement. By establishing an ET0 experimental condition recognized among the international research community, this study would test a number of widely used ET0 formulae using the measured ET0 from weighing lysimeters in the semi-arid climate in China to reveal the suitability and deviation of these formulae; Three aspects, the input driving parameters, model parameters and calculation sclae, would be examined in detail to clarify the main cause of the above deviation; Parameter optimization and calibration would be investigated to correct the above deviation; Finally, the ET0 formulae of various complexity and parameters applicable to the semi-arid climate in China would be recommeneded or established. Meanwhile, by simultaneously measuring ET0 with both the Bowen ratio system and lysimeters, the feasibility and ways of obtaining ET0 would be explored. The ET0 methods have never been systematically and experimentally tested under an internationally recognized reference crop in our country since their introduction. Thus, carryout of this study would be helpful to establish our own ET0 calculation guidelines and norms, and to avoid following blindly the FAO recommendations.

参考作物蒸散量ET0的准确计算是提高作物需水量估算精度的关键，因而是水资源科学管理中需要解决的重要问题。ET0试验研究的缺乏、驱动参数和模型参数选择依据的不足，导致目前作物用水估算的不确定性。本研究通过在半干旱气候区建立符合国际标准的参考作物试验条件，用称重式蒸渗仪测定ET0值来检验多种计算方法，揭示不同方法的适用性与偏差；并从影响ET0的驱动参数、模型参数及计算尺度入手，追踪偏差产生的主原因；最后通过优化参数算法或校正来消除偏差，建立适合我国半干旱气候区应用的繁简不等的ET0估算方法和参数。同时，通过波文比与蒸渗仪同步测定ET0，探索用波文比技术获得ET0实测值的可行性及方法。我国自引进ET0方法以来，还没有在符合国际标准的参照作物下作过系统的试验检验。本项目的开展有助于形成我国自己的ET0计算标准与规范，避免长期以来盲从FAO推荐方法的做法。

参考作物蒸散量（ET0）的准确计算是提高作物需水量估算精度的关键，因而是水资源科学管理中需要解决的重要问题。ET0试验研究的缺乏、驱动参数和模型参数选择依据的不足，导致目前作物用水估算的不确定性。本研究通过在半干旱气候区（北京昌平小汤山）建立符合国际标准的参考作物试验条件，用两台高精度（0.01mm）称重式蒸渗仪测定值检验了18种ET0计算方法（综合法、辐射法和温度法各6种），明确了不同方法的适用性与偏差；并从影响ET0的驱动参数及模型参数入手，探讨了产生偏差的主要原因；最后通过参数校正来降低偏差，推荐了适合我国半干旱气候区应用的繁简不等的ET0估算方法和参数。本研究的重要结果包括：1）综合法表现最好，均方根误差RMSE总体最低，为0.85~1.14 mmd-1，其中van Bavel Penman、1963 Penman、FAO-ppp-17 Penman同样好；辐射法次之，RMSE为1.23~1.63mmd-1，其中Turc方法最好；温度法最差，RMSE为1.17~2.40mmd-1，其中FAO24 Blaney-Criddle(BC)最好。不同方法的具体排序为：van Bavel Penman > 1963 Penman > FAO-ppp-17 Penman > 1996 Kimberly Penman > FAO56 Penman- Monteith (PM) > FAO24 Penman > FAO24 BC > Turc > DeBruin-Keijman > Priestley-Taylor (PT) > Jensen-Haise > Hargreaves > FAO24 Radiation > Makkink > Oudin > Hamon > BC > Mcloud。表现最好的2个综合法比常用的FAO56 PM、PT及Hargreaves法精度分别高33%、51%及65%。2）.综合法、辐射法及温度法的Hargreaves及FAO24 BC具有稳健的公式结构，对这些方法只需参数校正就能改善精度。多数温度法具有结构缺陷，参数校正对这些方法不适用，需通过结构优化进行改进。3）表现最好的3个综合法及辐射法更适用于湿润、低风条件，而表现较差的FAO56 PM和FAO24 Penman更适用于湿润、低辐射条件，Hargreaves在干燥或高辐射与高温差条件