不同e_a计算方法对Penman-Monteith公式的影响

实际水汽压ea是Penman-Monteith公式中计算参考作物蒸发蒸腾量的重要过程参数.为了研究在湿度缺测条件下,露点温度法替代相对湿度法计算ea在我国长江三角洲地区的适用性,选用江苏南通2000~2004年的旬气象资料,采用FAO推荐的相对湿度法和露点温度法两种方法计算了实际水汽压ea和旬参考作物蒸发蒸腾量ET0,分析了这两种方法计算结果的误差及其与影响因素间的关系.结果表明:这两种方法计算结果间误差较小,有98%以上的计算结果其误差小于20%;实际水汽压间的误差差异与最高最低温差相关关系最强,旬参考作物蒸发蒸腾量间的误差差异与最低温度的相关性最强;在湿度缺测条件下,可以采用露点温度法替代相对湿度法计算ea并进一步计算ET0.

Influence of e_a on calculation of reference crop evapotranspiration with Penman-Monteith formula

The actual water vapor pressure e_a is an important parameter to determine reference crop evapotranspiration ET_0 by Penman-Monteith formula.Generally,e_a is derived from relative humidity.The study was performed to investigate the applicability of the dewpoint temperature method replacing relative humidity for calculating e_a in the absence of humidity data in the Yangtze River Delta of China.With the ten-day meteorological data of Nantong City in Jiangsu Province from 2000 to 2004,e_a was derived from relative humidity and dewpoint temperature recommended by FAO,and ET_0 was determined by PenmanMonteith formula.The analysis of the difference between the calculated results of the two methods and its relationship with the meteorological factors shows that the difference between the two calculated results is small,and the rate with the difference less than 20% is over 98%.It is also concluded that the difference of e_a between the two methods is the most highly correlative with the difference between the highest and lowest temperatures,and that the difference of ET_0 is the most highly correlative with the lowest temperature.As a result,dewpoint temperature can replace relative humidity for calculating e_a and ET_0 in the absence of humidity data.