Angstrom公式参数对ET0的影响及FAO建议值适用性评价

作为计算太阳总辐射(R_s)的主要公式,Angstrom公式参数(a、b)的合理取值是计算参照腾发量(ET₀)的重要前提。针对FAO所提出的a、b建议值(a=0.25、b=0.5)在中国无辐射观测资料地区被大量使用,而其合理性尚未得到系统评价的情况,基于中国104个地面站的观测数据,在逐月时间尺度上,讨论了a、b变化对ET₀的影响,分析了a、b的地区分布规律,评价了FAO建议值所导致的ET₀计算误差,进而阐明了该建议值在中国7个区域的适用性。提出了无辐射资料情况下a、b的地区综合取值方法。主要研究结论是:①参数a、b偏差对ET₀的计算有重要影响,在中国无资料地区采用FAO建议值将导致较大的太阳总辐射(R_s)和ET₀计算误差。②大多数站点,a的率定值较FAO建议值明显偏小,而b的率定值明显偏大。新疆地区和华南地区a、b率定值分布比较集中,而在其它区域比较分散。③FAO建议参数值在东北、西北和新疆3个区域计算ET₀的适用性较好,而在西南和华南两个区域的适用性很差,计算的ET₀偏高较大。④提出的地区综合取值方法,能使R_s和ET₀的计算精度较FAO建议值显著提高。

Effects of Angstrom coefficients on ET0 estimation and the applicability of FAO recommended coefficient values in China

As a commonly used method of calculating global solar radiation(R_s),the determination of the Angstrom coefficients(a and b)values play a vital role to the success of estmiating the reference crop evapo transpiration (ET₀).At present, the values of 0.25 for a and 0.5 for b are used in the ungauged regions of China.Such values are recomm ended by the Food and Agriculture Organization of the United Nations(FAO).However,a comprehensive assessment of the applicability of FAO recommended values in China must be done before they can be used with confidence to calculate global solar radiation.In this study,the effect of a and b on ET₀ estmiation is investigated using the surface clmiatologic and solar radiation data measured at 104 meteorological stations distributed in China.Monthly values of a and b are calibrated with the observations,and their spatial and temporal variations are examined.The applicability of FAO recommended values in ET₀ estmiation is tested over 7 geographic regions.A new regional method for determinating the Angstrom coefficient a and b values is proposed for China ungauged regions.The main conclusions of this study are:(1)ET₀ is sensitive to the variability of a and b.The ET₀ estmiate may contain a large error resulting from the use of FAO recommended values in Rs calculation in certa in regions.(2)The calibrated value of a at most stations is significantly smaller than 0.25 that is recommended by FAO,and the value of b is however much greater than 0.50.For example,in Xinjiang autonomous region and South China,the calibrated values of a and b exhibit are latively uniformed distribution,however this is not the case over other regions.(3)The FAO recommended values are useful in ET₀ estimation with an acceptable accuracy in the areas of Xinjiang autonomous region,Northeast and Northwest China.However,the FAO values can result in severe overestmiation of ET₀ in the regions of South and Southwest China.(4)A new regional method for estimating a and b is proposed,which can give a satisfactory result of ET₀ estmiation when comparing to that of using the FAO recommended values.