American Society of Civil Engineers


Comparison of Standardized Reference Evapotranspiration Equations in Southern Spain


by Pedro Gavilán, (corresponding author), (Researcher, Natural Res. Dept., IFAPA, Centro de Investigatión y Formación Agraria “Alameda del Obispo,” Avd. Menéndez Pidal s/n, 14004 Córdoba, Spain E-mail: pedrod.gavilan@juntadeandalucia.es), Javier Estévez, (Grad. Student, Natural Resource D ept., IFAPA, Centro de Investigatión y Formación AGraria “Alameda del Obispo,” Avd. Menéndez Pidal s/n, 14004 Córdoba, Spain. E-mail: javier.estévez.ext@juntadeandalucia.es), and Joaquín Berengena, (Researcher Leader, Natural Resource Dept., IFAPA, Centro de Investigación y Formación Agraria “Alameda del Obispo,” Avd. Menéndez Pidal s/n, 14004 Córdoba, Spain. E-mail: joaquin.berengena@juntadeandalucia.es)

Journal of Irrigation and Drainage Engineering, Vol. 134, No. 1, January/February 2008, pp. 1-12, (doi:  http://dx.doi.org/10.1061/(ASCE)0733-9437(2008)134:1(1))

     Access full text
     Purchase Subscription
     Permissions for Reuse  

Document type: Journal Paper
Abstract: ASCE and FAO-56 standardized reference evapotranspiration (ET0) equations were compared using data from 31 meteorological stations in Andalusia, Southern Spain. Comparisons were made between daily ET0 obtained by summing hourly standardized ASCE — Penman — Monteith estimations and calculated from the addition of hourly FAO56 — Penman — Monteith estimations, daily ET0 estimated on a daily basis, and calculated by the Hargreaves equation. On an hourly basis, the FAO-56 version estimated lower than the ASCE version as 6% in some locations, with a difference of 4% on the average, mainly due to the higher surface resistance (70 s m-1) used in the FAO-56 version during daytime periods, as opposed to the 50 s m-1 rs value used by the ASCE version. Differences between both estimates were higher when evaporative demand increases. The level of agreement improved when the two computational time steps were compared, because differences were lower (2% on the average) and did not depend on the wind speed or ET0 values. The Hargreaves equation showed a higher spatial variability. At coastal areas, the equation generally underpredicted ASCE Penman — Monteith ET0 and provided good estimations for inland locations. Accuracy of the equation was affected by annual averages of evaporative demand and wind speed.


ASCE Subject Headings:
Data analysis
Evapotranspiration
Meteorology
Spain
Standardization