Journal of the American Water Resources Association a C O W M I S O N of Six P O T E M W Evmotwspiration Mthods for Regional Use in the Soutmastern M T E D Stams1

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. (KEY TERMS: potential evapotranspiration; actual evapotranspiration; forest hydrology; regional hydrological modeling; southeastern

[1]  H. L. Penman.  Natural evaporation from open water, bare soil and grass , 1948, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[2]  W. Brutsaert,et al.  A comparison of several evaporation equations , 1992 .

[3]  Charles J Vörösmarty,et al.  Potential evaporation functions compared on US watersheds: Possible implications for global-scale water balance and terrestrial ecosystem modeling , 1998 .

[4]  G. McCabe,et al.  SPATIAL VARIABILITY IN WATER‐BALANCE MODEL PERFORMANCE IN THE CONTERMINOUS UNITED STATES 1 , 2002 .

[5]  M. Wu,et al.  Principles of environmental physics , 2004, Plant Growth Regulation.

[6]  Ge Sun,et al.  MODELING THE FOREST HYDROLOGY OF WETLAND‐UPLAND ECOSYSTEMS IN FLORIDA 1 , 1998 .

[7]  H. Riekerk.  Influence of silvicultural practices on the hydrology of pine flatwoods in Florida , 1989 .

[8]  Lawrence E. Band,et al.  Ecosystem processes at the watershed scale: Sensitivity to potential climate change , 1996 .

[9]  D. Currie.  Energy and Large-Scale Patterns of Animal- and Plant-Species Richness , 1991, The American Naturalist.

[10]  R. Allen,et al.  Evapotranspiration and Irrigation Water Requirements , 1990 .

[11]  C. Priestley,et al.  On the Assessment of Surface Heat Flux and Evaporation Using Large-Scale Parameters , 1972 .

[12]  Richard L. Snyder,et al.  Pan Evaporation to Reference Evapotranspiration Conversion Methods , 2002 .

[13]  C. W. Thornthwaite.  An Approach Toward a Rational Classification of Climate , 1948 .

[14]  C. Federer,et al.  Brook: A Hydrologic Simulation Model for Eastern Forests , 1978 .

[15]  Lysimetric Evaluation of Pine Forest Evapotranspiration , 1985 .

[16]  A. Martínez-cob,et al.  A wind-based qualitative calibration of the Hargreaves ET0 estimation equation in semiarid regions , 2004 .

[17]  C. Stöckle,et al.  Comparison of methods for applying the Priestley–Taylor equation at a regional scale , 2001 .

[18]  Ge Sun,et al.  MODELING ACTUAL EVAPOTRANSPIRATION FROM FORESTED WATERSHEDS ACROSS THE SOUTHEASTERN UNITED STATES 1 , 2003 .

[19]  E. J. Winter.  The Water Balance , 1974 .

[20]  Devendra M. Amatya,et al.  Comparison of methods for estimating REF-ET , 1995 .

[21]  G. P. Fernandez,et al.  Hydrology of Poorly Drained Coastal Watersheds in Eastern North Carolina , 2002 .

[22]  G. Sun,et al.  Water budgets of two forested watersheds in South Carolina , 2000 .

[23]  J. Stein,et al.  Estimation of potential evapotranspiration with shallow lysimeters in a forest tree nursery , 1995 .

[24]  S. Durrans,et al.  A REVISED VERSION OF PnET‐II TO SIMULATE THE HYDROLOGIC CYCLE IN SOUTHEASTERN FORESTED AREAS 1 , 2002 .

[25]  George H. Hargreaves,et al.  Reference Crop Evapotranspiration from Temperature , 1985 .

[26]  M. Arthur,et al.  EFFECTS OF BEST MANAGEMENT PRACTICES ON FOREST STREAMWATER QUALITY IN EASTERN KENTUCKY 1 , 1998 .

[27]  Charles J Vörösmarty,et al.  Intercomparison of Methods for Calculating Potential Evaporation in Regional and Global Water Balance Models , 1996 .