遗传算法率定参照作物腾发量相关参数的研究

用气象资料计算参照作物腾发量(ET0)的方法需要各种气象(候)和物理参数,净辐射是其中的重要数据之一,而专业测量净辐射的设备在农业气象站里很少安装。为解决计算ET0时缺少太阳净辐射(Rn)测量值这一实际问题,该文采用浑善达克沙地东南缘南沙梁草甸草原区气象站观测的气象资料,用遗传算法模型对联合国粮农组织56号文本(FAO56)推荐值(as和bs)进行率定,计算了对应夏半年(4—9月)和冬半年(1—3月和10—12月)的太阳净辐射和参照作物腾发量,并将率定前后的模拟太阳辐射进行对比分析,用残差估计指数法对该方法模拟的参照作物腾发量模拟精度进行了分析。结果表明:在缺少太阳净辐射测量值的地区,采用FAO56参数(as和bs)推荐值与遗传算法模型率定参数(as和bs)相比,净辐射年内变化趋势一致,采用率定后参数计算的净辐射相对更不稳定,波动更大,但能有效提高参照作物腾发量计算精度。误差较大的模拟值均出现在降雨日前后,降雨虽然并未直接出现在Penman-Monteith公式中,但是降雨必然会对湿度和温度等气象条件造成一定影响,而as和bs是受湿度等因素影响而变化的,其深层次的原因有待进一步分析。

Calibration of relevant parameters of reference crop evapotranspiration with genetic algorithm

The existing methods of calculating reference crop evapotranspiration (ET₀) from meteorological data need various climatic and physical parameters. Net radiation (R_n) is one essential parameter for ET₀. However, professional measurement devices of Rn are seldom installed in agro-meteorological stations. To overcome problems in calculating ET₀ without R_n data, a genetic algorithm model was used to calibrate recommended values (a_s and b_s) of the FAO56 method, using meteorological data from Nanshaliang Meadow Steppe in the southeastern margin of Hunshandake. R_n and the corresponding ET₀ for April to September and October to March were calculated and the pre-calibration solar radiation compared with that of post-calibration. The simulation accuracy of ET₀ was analyzed using the estimated residual index method. From comparison of the result using recommended and calibrated values (a_s and b_s), a consistent annual trend was noted for simulated Rn in areas without R_n data. Although Rn obtained from calibrated values was unstable with high fluctuations, the overall accuracy of ET₀ improved. The analysis showed that large error immediately before and after precipitation events. Although precipitation factor is not directly included in the Penman-Monteith equation, it certainly influences local humidity and temperature. Apparent, both a_s and b_s were affected by changes in humidity. There was therefore the need to further analyze these parameters in relation to humidity.