Simple Equation to Estimate Reference Evapotranspiration from Evaporation Pans Surrounded by Fallow Soil

• Published in: Journal of irrigation and drainage engineering 2008-08, Vol.134 (4), p.425-429
• Main Authors: Abdel-Wahed, Mohamed H, Snyder, Richard L
• Format: Article
• Language: English
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agricultural and forest meteorology; agricultural soils; Agronomy. Soil science and plant productions; Biological and medical sciences; environmental models; equations; estimation; evaporation; evapotranspiration; fallow; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; humidity; Irrigation. Drainage; mathematical models; simulation models; TECHNICAL PAPERS; Water balance and requirements. Evapotranspiration
• ISSN: 0733-9437; 1943-4774
• DOI: 10.1061/(ASCE)0733-9437(2008)134:4(425)

Reliable estimates of reference evapotranspiration ( ET0 ) are key elements for efficient water resource management, and estimating ET0 , based on “Class ‘A’ pan evaporation” data is common in arid climates. A pan coefficient ( Kp ) , which depends on the distance (or fetch) of green vegetation or fallow soil around the pan (F) , wind run (U) , and relative humidity (RH), is used to convert from pan evaporation to ET0 . Several researchers have developed models for estimating Kp values for pans surrounded by green vegetated fetch, but there is only one equation to estimate Kp values for dry fetch conditions. The equation is complex, so the objective of this research was to develop a new simple equation to estimate Kp under fallow soil fetch conditions. The new Kp equation and the more complex equation were compared with tabular values published by the United Nations Food and Agriculture Organization. The new equation performed slightly better at matching the tabular Kp values than the complex equation. The equation derivation and evaluation are presented.