Estimating actual, potential, reference crop and pan evaporation using standard meteorological data: a pragmatic synthesis

Abstract

Abstract. This guide to estimating daily and monthly actual, potential, reference crop and pan evaporation covers topics that are of interest to researchers, consulting hydrologists and practicing engineers. Topics include estimating actual evaporation from deep lakes and from farm dams and for catchment water balance studies, estimating potential evaporation as input to rainfall-runoff models, and reference crop evapotranspiration for small irrigation areas, and for irrigation within large irrigation districts. Inspiration for this guide arose in response to the authors' experiences in reviewing research papers and consulting reports where estimation of the actual evaporation component in catchment and water balance studies was often inadequately handled. Practical guides using consistent terminology that cover both theory and practice are not readily available. Here we provide such a guide, which is divided into three parts. The first part provides background theory and an outline of the conceptual models of potential evaporation of Penman, PenmanMonteith and Priestley-Taylor, as well as discussions of reference crop evapotranspiration and Class-A pan evaporation. The last two sub-sections in this first part include techniques to estimate actual evaporation from (i) open-surface water and (ii) landscapes and catchments (Morton and the advection-aridity models). The second part addresses topics confronting a practicing hydrologist, e.g. estimating actual evaporation for deep lakes, shallow lakes and farm dams, lakes covered with vegetation, catchments, irrigation areas and bare soil. The third part addresses six related issues: (i) automatic (hard wired) calculation of evaporation estimates in commercial weather stations, (ii) evaporation estimates without wind data, (iii) at-site meteorological data, (iv) dealing with evaporation in a climate change environment, (v) 24 h versus day-light hour estimation of meteorological variables, and (vi) uncertainty in evaporation estimates. This paper is supported by a Supplement that includes 21 sections enhancing the material in the text, worked examples of many procedures discussed in the paper, a program listing (Fortran 90) of Morton's WREVAP evaporation models along with tables of monthly Class-A pan coefficients for 68 locations across Australia and other information.

Future discharge drought across climate regions around the world modelled with a synthetic hydrological modelling approach forced by three general circulation models

“…The model is forced with daily temperature, precipitation and potential evapotranspiration to enable snow accumulation, soil moisture, actual evapotranspiration and discharge simulations. Estimates of daily evapotranspiration are calculated using the Penman-Monteith reference evapotranspiration (McMahon et al, 2013). The potential evapotranspiration was calculated from daily temperature (minimum, Figure 1.…”

Estimation of evapotranspiration of temperate grassland based on high-resolution thermal and visible range imagery from unmanned aerial systems

“…Information on the magnitude of evapotranspiration (ET) from land surfaces, along with its variability in space and time, is essential for effectively managing water resources in agricultural systems (Anderson et al 2011; Bastiaanssen et al 2005; Cammalleri et al 2014; Carlson 2007; Chirouze et al 2014; Cleugh et al 2007; Jiang and Islam 2001; Kustas et al 2012; McMahon et al 2013; Morillas et al 2013; Tang et al 2011). However, the regional quantification of ET remains difficult, in particular when spatially distributed information with high resolution is sought.…”

Interactions of artificial lakes with groundwater applying an integrated MODFLOW solution

“…The daily lake evaporation was computed using the Penman open-water equation (Penman 1948) on the base of hourly incoming solar radiation, relative humidity, wind speed, air temperature and using the wind-speedfunction constant values recommended by McMahon et al (2013). The daily lake evaporation ranged from (Fig.…”

“…For the land surface (total model area minus lake area), the daily potential evapotranspiration (PET) was estimated using hourly incoming solar radiation, relative humidity, wind speed, air temperature, and soil heat flux following the McMahon et al (2013) definition of potential evapotranspiration considered as "the rate at which evapotranspiration would occur from a large area completely and uniformly covered with growing vegetation, which has access to an unlimited supply of soil water, and without advection or heating effects". In line with that definition, first, the reference evapotranspiration (ET o ) using the "FAO Penman Monteith" method (Allen et al 1998) was estimated, and then, by using the "single crop coefficient" method, the ET o was converted to daily crop potential evapotranspiration considered as potential evapotranspiration (PET).…”