A Graphical Interpretation of the Rescaled Complementary Relationship for Evapotranspiration. Issue 8 (10th August 2021)

• Record Type: Journal Article
• Authors: Crago, Richard D.; Qualls, Russell J.
• Is Part Of: Water resources research. Volume 57:Issue 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-08-10
• Subjects: evaporation -- evapotranspiration -- Complementary Relationship -- energy budget -- conceptual methods -- graphical methods; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2020WR028299
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Wet‐surface evaporation equations related to the Penman equation can be represented graphically on vapor pressure ( e ) versus temperature ( T ) graphs (Qualls & Crago, 2020, https://doi.org/10.1029/2019wr026766 ). Here, actual regional evaporation is represented graphically on ( e, T ) graphs using the Complementary Relationship (CR) between actual and apparent potential evaporation. The CR proposed by the authors can be represented in a simple and intuitive geometric form, in which lines representing the regional latent heat flux, LE, and the wet surface (Priestley & Taylor, 1972, https://doi.org/10.1175/1520-0493(1972)100<0081:otaosh>2.3.co;2 ) evaporation rate, LEPT, intersect at e = 0. This approach allows a graphical estimate of LE (or the corresponding mathematical formulation), provided available energy, wind speed, air temperature and humidity, and roughness lengths for momentum and sensible heat are available. The wet surface temperature is needed, and a calculation method for it is provided. The formulation works well using monthly data from seven sites in Australia, even when the same value of the Priestley & Taylor parameter α is used for all sites. Overall, compared to eddy covariance measurements, root mean square difference averaged 19 W m −2 ; this compares favorably with the CR formulation proposed by Brutsaert (2015, https://doi.org/10.1002/2015wr017720 ). Plain Language Summary: The Complementary Relationship (CR) between actual regional evaporation and apparent potential evaporation has received considerable support in recent years. Here, a representation of one version of the CR is developed and expressed on a single temperature/vapor pressure graph. Features such as available energy, wet surface temperature, actual surface temperature, potential temperature, and apparent potential temperature are all clearly represented graphically. The method is compared with that proposed by Brutsaert (2015, https://doi.org/10.1002/2015wr017720 ). Both methods performed well, but the graphical method has lower root mean squared errors. Key Points: Latent heat flux or evaporation can be depicted on graphs of vapor pressure ( e ) versus temperature ( T ) The Complementary Relationship (CR) of evaporation can be expressed graphically using an e versus T graph The CR performs well with data from seven sites in Australia