修正Hargreaves-Samani公式估算宁夏参考作物蒸散量适用性分析

Adaptability analysis of modified Hargreaves——Samami formula for estimating reference crop evapotranspiration in Ningxia

Hargreaves-Samani(HS)公式是运用气温和太阳辐射气象数据计算参考作物蒸散量(ET0)的方法。基于贝叶斯原理(HScor公式)以及最小二乘法原理(HS_(lsq)公式),利用宁夏回族自治区(以下简称宁夏)10个代表气象站点1961—2006年逐日气象数据对HS公式中参数进行修正,并以2007—2016年Penman-Monteith(PM)公式的计算值(ET_(OPM))为标准,评价两种修正公式在宁夏北部引黄灌区(Ⅰ区)、中部干旱带(Ⅱ区)以及南部山区(Ⅲ区)的计算精度与适用性。评价结果表明,HScor公式各参数在3个分区差别不大,且均不大于FAO(Food andAgricultureOrganization)提出的修正值,HS_(lsq)公式各参数在3个分区的差别较大;与逐日ET_(OPM)相比,两种修正公式计算的逐日参考作物蒸散量值ET_(Ocor)和ETOlsq的归一化均方根误差值(nRMSE)在Ⅰ区从22.86%分别降至21.08%和22.16%,Ⅱ区从23.69%分别降至22.19%和22.26%,Ⅲ区从23.40%分别降至20.12%和20.22%,HScor公式的nRMSE降低幅度最大;相关性分析表明,ET_(Ocor)与ET_(OPM)相关系数最高(0.9447),达到显著相关;在7—9月,逐月HS公式计算的参考作物蒸散量值ETOHS的nRMSE最高,为7.10%,逐月ET_(Ocor)和ETOlsq的nRMSE分别降低了5.11%和1.78%。因此,HScor公式在宁夏3个分区的参考作物蒸散量计算精度较高,可作为宁夏参考作物蒸散量简化计算的推荐公式。

Hargreaves-Samani(HS)formula is a simplified method to estimate reference crop evapotranspiration(ET0)by using the meteorological data of temperature and solar radiation.Based on the Bayesian Theory(HScor formula)and Least Square Theory(HSlsq formula),the daily meteorological data of 10 representative meteorological stations in Ningxia Hui Autonomous Region from 1961 to 2006 were used to modify the parameters in the HS formula.Taking the calculated value of Penman-Monteith formula(ET_(OPM))from 2007 to 2016 as the standard,the calculation accuracy and applicability of the two modified formulas were evaluated in the northern Yellow River diversion irrigation zone(ZoneⅠ),the central arid zone(ZoneⅡ),and the southern mountainous zone(ZoneⅢ)of Ningxia.The results show that the parameters of HScor formula have little difference in three partitions and are not greater than the modified values proposed by FAO,while the parameters of HSlsq formula have great difference in three partitions.Compared with daily ET_(OPM),the normalized root mean square error(nRMSE)of daily ET_(Ocor) value and ET_(OPM) value calculated by two modified formulas decrease from 22.86%to 21.08%and 22.16%in ZoneⅠ,respectively;from 23.69%to 22.19%and 22.26%in ZoneⅡ,and from 23.40%to 20.12%and 20.22%in ZoneⅢ.The nRMSE of HScor formula decreased the most.The correlation analysis shows that the correlation coefficient between ET_(Ocor) and ET_(OPM) was the highest(0.9447),which reaching a significant correlation.From July to September,the nRMSE of monthly ETOHS value was the highest,which was 7.10%,while the nRMSE of monthly ET_(Ocor) and ETOlsq decreased by 5.11%and 1.78%,respectively.Consequently,the modified HScor formula based on Bayesian Theory has a high accuracy in the calculation of ET0 in the three regions of Ningxia,and can be used as the recommended formula for the simplified calculation of ET0 in Ningxia.