A Comparison of Six Potential Evapotranspiration Methods for Regional Use in the Southeastern United States

Abstract

Potential evapotranspiration (PET) is an important index of hydrologic budgets at different spatial scales and is a critical variable for understanding regional biological processes. It is often an important variable in estimating actual evapotranspiration (AET) in rainfall‐runoff and ecosystem modeling. However, PET is defined in different ways in the literature and quantitative estimation of PET with existing mathematical formulas produces inconsistent results. The objectives of this study are to contrast six commonly used PET methods and quantify the long term annual PET across a physiographic gradient of 36 forested watersheds in the southeastern United States. Three temperature based (Thornthwaite, Hamon, and Hargreaves‐Samani) and three radiation based (Turc, Makkink, and Priestley‐Taylor) PET methods are compared. Long term water balances (precipitation, streamflow, and AET) for 36 forest dominated watersheds from 0.25 to 8213 km2 in size were estimated using associated hydrometeorological and land use databases. The study found that PET values calculated from the six methods were highly correlated (Pearson Correlation Coefficient 0.85 to 1.00). Multivariate statistical tests, however, showed that PET values from different methods were significantly different from each other. Greater differences were found among the temperature based PET methods than radiation based PET methods. In general, the Priestley‐Taylor, Turc, and Hamon methods performed better than the other PET methods. Based on the criteria of availability of input data and correlations with AET values, the Priestley‐Taylor, Turc, and Hamon methods are recommended for regional applications in the southeastern United States.

The impact of forest regeneration on streamflow in 12 mesoscale humid tropical catchments

“…The choice for the empirical Hargreaves method was motivated on the one hand by the lack of available long-term data for the climatic variables required for more physically based methods such as the Penman-Monteith equation (Monteith, 1965), and on the other hand by the better availability of T min and T max data. The Hargreaves method has been evaluated successfully against PET based on the Penman-Monteith equation (Trajkovic, 2007) and various other equations (Lu et al, 2005;Sperna Weiland et al, 2012).…”

Environmental controls on seasonal ecosystem evapotranspiration/potential evapotranspiration ratio as determined by the global eddy flux measurements

“…The ratio of AET / PET or water stress level can be drastically different among different ecosystems in different environmental conditions, because AET is mainly controlled by climate (precipitation and PET) (Zhang et al, 2001;Jaramillo et al, 2013) and ecosystem species composition and structure (i.e., leaf area index, rooting depth) (Sun et al, 2011a;Hasper et al, 2016). The same seasonal PET values for a particular region are generally stable among different years (Lu et al, 2005;Rao et al, 2011), and deviation of AET / PET from the norm indicates variability in AET, which responds to precipitation and water availability when PET is stable (Rao et al, 2011). However, under a changing climate, the monthly AET / PET patterns can be rather complex since both AET and PET are affected by air temperature and precipitation (Sun et al, 2015a, b) and corresponding changes in ecosystem characteristics (e.g., plant species shift) (Donohue et al, 2007;Vose et al, 2011;Sun et al, 2014).…”

Propagation of biases in humidity in the estimation of global irrigation water

“…The performance of these formulae has been examined in comparison with observed data at various spatial and temporal scales (e.g., Winter et al, 1995;Federer et al, 1996;Vörösmarty et al, 1998;Lu et al, 2005;Rao et al, 2011). Descriptions of these formulae are also given in the abovementioned references and in Shelton (2009); however, here we give some examples of the two types of formulae (physical and empirical; see also Sect.…”

“…Different evapotranspiration formulae adopted in different GHMs may be a source of differences in evapotranspiration among GHMs. The performance of the various evapotranspiration formulae that have been proposed has been primarily examined in comparison with the results of in situ observation (e.g., Winter et al, 1995;Federer et al, 1996;Vörösmarty et al, 1998;Lu et al, 2005;Rao et al, 2011) at various geographical scales. As described in Sect.…”