Efforts to standardize evapotranspiration (ET) methodology have progressed over the last few decades, yet confusion about ET terminology remains. To provide a more reliable foundation for communications in water resource planning and irrigation management, a new technical note is now publicly available in ASCE Journal of Irrigation and Drainage Engineering, titled “Evapotranspiration Terminology and Definitions”. This important resource defines 30 terms related to ET (the combination of water evaporation and plant transpiration) and clarifies many nuances of ET measurement and estimation methods, including crop coefficient approaches, applications to nonagricultural vegetation, practical guidelines for reference ET calculation, encouragement to replace “potential ET” terminology with better terms, ET products from remote sensing, role of ET in water rights, and illustrations to clarify the meaning of various ET terms.
This technical note will serve as a comprehensive reference guide for ET practitioners and researchers, including hydrologists, irrigation engineers and specialists, agricultural scientists and agronomists, farmers and landscapers, climatologists and meteorologists, water resource managers and planners, environmental scientists, policy makers and regulators, consulting engineers and technical advisors, and students of hydrology, agriculture, and environmental sciences.
This important paper was spearheaded by the ASCE-EWRI Evapotranspiration in Irrigation and Hydrology Committee, a national group of experts in ET. Writing of this technical note was highly collaborative, with over 27 coauthors contributing. Input on drafts of the paper was solicited from dozens of stakeholders including state and Federal agencies, irrigation and water resource organizations, industry partners, researchers, and international groups, and over 50 stakeholders wrote letters of support for the project. Finally, this technical note was written in collaboration with 2025 updates to the American Society of Agricultural and Biological Engineers (ASABE) standards on soil and water nomenclature, to ensure consistent terminology among multiple professional groups.
The open-source technical note can be found here.
References:
ASABE. 2025. "Standard ASAE S526.5 MAR2025ED Soil and Water Terminology." St. Joseph, MI: ASABE.
DeJonge, K.C., R.G. Allen, A. Kilic, K.R. Thorp, M. Kukal, G.W. Marek, J. Altenhofen, D. Amatya, P. Blankenau, S. Datta, G. Grabow, A. Hashem, I. Kisekka, J. Kjaersgaard, T. Marek, T. Peters, D. Porter, M. Reba, D. Rudnick, G. Senay, V. Sharma, V. Sridhar, G. Sun, S. Taghvaeian, R. Trezza, T. Trout. 2025. Evapotranspiration terminology and definitions. ASCE Journal of Irrigation and Drainage Engineering. https://doi.org/10.1061/JIDEDH/IRENG-10491