A comparison of ASCE and FAO-56 reference evapotranspiration for a 15-min time step in humid climate conditions

作者：Suleiman Ayman A; Hoogenboom Gerrit^*

来源：Journal of Hydrology, 2009, 375(3-4): 326-333.

DOI：10.1016/j.jhydrol.2009.06.020

• Canopy resistance
• Evapotranspiration
• Georgia Automated Environmental
• Monitoring Network
• Penman-Monteith equation

Many applications in diverse disciplines require estimates of evapotranspiration (ET) at hourly or smaller time steps. The primary objectives of this study were to compare the American Society of Civil Engineers (ASCE) and FAO-56 Penman-Monteith equations for 15-min ET(0) (ET(0,15-min,ASCE) and ET(0,15-min,FAO)) estimations for humid climate conditions and to compare the 24 h sum of ASCE (ET(0.24) (h,ASCE)) and FAO-56 15-min ET(0) (ET(0,24) (h,FAO)) with the daily ET(0) (ET(0,d,FAO)) computed from the daily FAO-56 equation, which is identical to ASCE daily ET(0) equation. Ten-year, i.e., 1997-2006 continuous 15-min and daily weather data for 11 representative and well-distributed sites throughout Georgia, USA were used. It was evident that during the day, ET(0,15-min,ASCE) was higher than ET(0,15-min),FAO due to a lower surface resistance parameter value, while at night ET(0,15-min,ASCE) was lower than ET(0,15-min,FAO) due to a higher surface resistance parameter value. The ET(0,15-min,FAO) Was about 5% less than ET(0,15-min-ASCE) and ET(0,24 h,FAO) was about 5% lower than ET(0,24) (h,ASCE). The difference between ET(0,15-min,ASCE) and ET(0,15-min,FAO) during the day and night was highly dependent on wind speed. During the three summer months, i.e., June, July and August, on average, ET(0,24) (h,FAO) was only 1% higher than ET(0,d,FAO) while ET(0,24) (h,ASCE) was 5% higher than ET(0,d,FAO). For the entire year, ET(0,24) (h,FAO) was 8% higher than ET(0,d,FAO) while ET(0,24) (h,ASCE) was 13% higher than ET(0,d,FAO). The ET(0,24 h,FAO) and ET(0,d,FAO) had a better agreement than ET(0,24) (h,ASCE) and ET(0,d,FAO) throughout the year during the summer months. It is also worth noting that the daily calculations for FAO-56 and ASCE were identical. These results demonstrated that for applications that require 15-min time steps or daily ET(0) for the entire year, the use of ET(0,15-min,FAO) and ET(0,24) (h,FAO), respectively, will yield more consistent outcomes. The use of ET(0,d,FAO) during the summer months can be as accurate as the use of ET(0,24 h,FAO) for applications that require daily time steps, such as irrigation scheduling.

• 出版日期2009-9-15