Hargreaves公式在中国农业区的年内回归修正

针对中国范围的Hargreaves(HS)公式线性回归修正研究缺少,区域或站点的修正系数存在时空尺度不统一、推广应用困难的问题,以中国气象数据网发布的中国地面气候资料月值数据集和中国辐射月值数据集中124个站点1957-2016年的气象要素逐月有效观测数据,首先,基于Penman-Monteith(PM)公式和HS公式分别计算各站点逐月的多年平均参考作物需水量ET_0-PM和ET_0-HS;其次,以ET_0-PM为真值,基于1957-2010年的逐月平均ET_0-PM和ET_0-HS,引入中国农业综合区划作为空间分区框架,通过回归分析获取中国38个陆地农业子区的HS公式校正系数a和b;最后,以2011-2016年为应用验证区间,通过逐月比较ET_0-HS校正前后的6 a平均相对误差,验证联合国粮农组织(FAO)推荐的HS公式校正方法在中国农业区的适用性,并进一步基于误差结果的对比分析,提出各农业区HS公式校正系数a和b的逐月最优取值方案.结果表明:各农业区之间回归计算的HS公式校正系数a和b并无明显的变化规律,但系数b稳定在0.8左右,系数a则在区域之间的差异较大,徘徊于-0.22~1.10;校正前后的ET_0-HS均存在不同程度的误差,但校正后的ET_0-HS误差明显降低,平均相对误差降低了20%,最大相对误差降低约100%.因此经验证,FAO推荐的HS公式回归校正方法简单易行,可操作性强,对中国各农业区大规模使用简化的方式快速获得较准确的参考作物需水量,具有一定的推广价值.

Regression correction of Hargreaves equation within a year in China′s agricultural regions

For the question that there is a lack of research on the linear regression correction of the Hargreaves Equation(HS)for entire China's Mainland,and the existing correction coefficient of regions or stations is not uniform in spatial and temporal scale and difficult to be popularized and applied.Meteorological data,which was included in the Dataset of Monthly Values of Radiation Data from Chinese Surface Stations and the Dataset of Monthly Values of Climate Data from Chinese Surface Stations,were obtained from 1957 to 2016 at 124 sites.Firstly,based on Penman-Monteith(PM)equation and the HS,the average reference crop evapotranspiration—ET0-PM and ET0-HS in each month were calculated.Secondly,using ET0-PM as the truth value,and based on the average ET0-PM and ET0-HS of each region from 1957 to 2010,the correction coefficients of a and b of the HS from 38 agricultural sub-regions in China were obtained by regression analysis.Finally,taking 2011—2016 as the application ve-rification interval,and the monthly change of 6 a mean relative error(RE)before and after correction of ET0-HS by the coefficients obtained from the corrected data was used to verify the applicability of HS correction method recommended by the Food and Agriculture Organization of the United Nations(FAO)in China′s agriculture regions.Based on the comparative analysis of the error results,the monthly optimal values of correction coefficients a and b of HS in each agricultural region were proposed.The results show that:The correction coefficients a and b of HS calculated by regression have no obvious change regularity in all agricultural regions,but the value of coefficient b is relatively stable around 0.8,and the coefficient a varies greatly from-0.22 to 1.10;ET0-HS before and after correction has different degree errors,but ET0-HS error after correction will be significantly reduced,with the average RE is reduced by 20%and the maximum RE is reduced by about 100%.Therefore,after verification,the method of HS correction suggested by FAO is simple and easy to operate,and has a certain popularization value for rapidly obtaining accurate ET0 by using simplified methods in various agricultural regions in China.