Performance of different methods for reference evapotranspiration estimation in Jaíba, Brazil

ABSTRACT FAO Penman-Monteith (FO-PM) is considered the standard method for the estimation of reference evapotranspiration (ET0) but requires various meteorological data, which are often not available. The objective of this work was to evaluate the performance of the FAO-PM method with limited meteorological data and other methods as alternatives to estimate ET0 in Jaíba-MG. The study used daily meteorological data from 2007 to 2016 of the National Institute of Meteorology’s station. Daily ET0 values were randomized, and 70% of these were used to determine the calibration parameters of the ET0 for the equations of each method under study. The remaining data were used to test the calibration against the standard method. Performance evaluation was based on Willmott’s index of agreement, confidence coefficient and root-mean-square error. When one meteorological variable was missing, either solar radiation, relative air humidity or wind speed, or in the simultaneous absence of wind speed and relative air humidity, the FAO-PM method showed the best performances and, therefore, was recommended for Jaíba. The FAO-PM method with two missing variables, one of them being solar radiation, showed intermediate performance. Methods that used only air temperature data are not recommended for the region.

摘要：FAO彭曼-蒙特斯法（FAO Penman-Monteith, FO-PM）被公认为参考作物蒸散量（reference evapotranspiration, ET₀）估算的标准方法，但该方法需依赖多种气象数据，而此类数据往往难以获取。本研究旨在评估有限气象数据条件下FAO-PM法的应用性能，并探索其他替代方法以在Jaíba-MG地区开展ET₀估算。研究采用了国家气象研究所（National Institute of Meteorology）观测站2007年至2016年的逐日气象数据。研究人员将逐日ET₀值进行随机划分，其中70%的数据用于校准各研究方法的ET₀估算方程参数，剩余数据则以标准方法为参照，对校准效果进行验证。性能评估以威尔莫特一致性指数（Willmott’s index of agreement）、置信系数及均方根误差（root-mean-square error）为评价指标。当仅缺失一种气象变量（太阳辐射、空气相对湿度或风速），或同时缺失风速与空气相对湿度时，FAO-PM法表现最优，因此推荐在Jaíba-MG地区使用该方法。当缺失两个变量且其中一个为太阳辐射时，FAO-PM法表现中等。仅使用气温数据的估算方法不适用于该区域。