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The US Hydrologic Data (GHAAS) collection contains data used to compare water balance estimates over U.S. watersheds modeled by eleven potential evapotranspiration functions as described in Vörösmarty et al. Potential evaporation functions compared on US watersheds: Possible implications for global-scale water balance and terrestrial ecosystem modeling, Journal of Hydrology 207 1998 pp.147-169.

Although the data may be used without restriction, there have been improvements to the climate input data sets in the years following the publication. The providers of these climate data sets encourage you to use their more recent data:

• Climate Data from University of Delaware: Updates
• Climate Data from the Potsdam Institute for Climate Impact Research: Updates

Please acknowledge the University of New Hampshire, EOS-WEBSTER Earth Science Information Partner (ESIP) as the data distributor for this dataset.

Summary:

The US Hydrologic Data (GHAAS) collection contains data used to compare water balance estimates over U.S. watersheds modeled by eleven potential evapotranspiration functions. The terrestrial water cycle is of critical importance to a wide array of Earth System processes. It plays a central role in climate and meteorology, plant community dynamics, carbon and nutrient biogeochemistry, and the structure and function of aquatic ecosystems. With a growing scientific consensus on the existence of CO₂-induced greenhouse warming comes an increasing level of concern about how this climatic change will affect the terrestrial water cycle.

The primary objective of this study is to compare a set of potential evaporation functions that are commonly employed in global-scale water balance and terrestrial net primary production models as a precursor to estimating the realized or "actual" evapotranspiration. We assess these functions at the continental-scale using input data and validation targets distributed across the relatively data-rich conterminous United States. The model comparison results and analysis are described in Vörösmarty et al. Potential evaporation functions compared on US watersheds: Possible implications for global-scale water balance and terrestrial ecosystem modeling, Journal of Hydrology 207 1998 pp.147-169.

Water Balance Model (WBM)

The water balance model used in the US Hydrologic Data (GHAAS) application simulates soil moisture variations, evapotranspiration, and runoff on single grid cells using biophysical data sets that include climatic drivers, vegetation, and soil properties. The state variables are determined by interactions among time-varying precipitation, potential evaporation, and soil water content. The original model is described in detail in Vörösmarty et al. (1989, 1996) and Vörösmarty and Moore (1991). For this application, the model was run to steady state using a set of climatologically-averaged datasets, described below.

General Information:

Spatial resolution: 0.5 x 0.5 deg., latitude x longitude grids.

Temporal resolution: monthly, model estimates for a long–term-mean year.

US Hydrologic Data (GHAAS) includes the following datasets and variables (A reference list follows the table):

References:

Black, J. 1956. The distribution of solar radiation over the Earth’s surface. In: Wind and Solar Energy. UNESCO, Paris, FRANCE, pp. 138-40.

Edwards, M.O., 1989. Global gridded elevation and bathymetry on 5-minute geographic grid, (ETOPO5). NOAA National Geophysical Data Center, Boulder, Colorado, USA.

FAO/UNESCO. 1977. Soil map of the world, 1: 5 000 000. UNESCO, Paris, FRANCE.

Geraghty, J.J., Miller, D.W., van der Leeden, F. and Troise, F.L., 1973. Water Atlas of the United States. Water Information Center, Port Washington, New York, USA.

Legates, D. R. and Willmott, C.J., 1990a. Mean seasonal and spatial variability in gauge-corrected, global precipitation. Int. J. of Climatology, 10: 111-127.

Legates, D. R. and Willmott, C.J., 1990b. Mean seasonal and spatial variability in global surface air temperature. Theoretical and Applied Climatology, 41: 11-21.

Melillo, J.M., McGuire, A.D., Kicklighter, D.W., Moore, B., Vörösmarty, C.J. and Schloss, A.L., 1993. Global climate change and terrestrial net primary production. Nature, 363:234-40.

Murray, F.W. 1967. On the computation of saturation vapor pressure. J. of Applied Meteorology, 6: 203-204.

Olson, J.S. 1989-91. World ecosystems digital raster data on global geographic 180x360 and 1080x2160 grids. NOAA National Geophysical Data Center, Boulder, Colorado, USA.

Saxton et al. (1986) Soil Sci. Soc. Am. J. 50:1031-1036.

Vörösmarty, C.J., Moore, B., Gildea, M.P., Peterson, B., Melillo, J., Kicklighter, D., Raich, J., Rastetter, E. and Steudler, P., 1989. A continental–scale model of water balance and fluvial transport: Application to South America. Global Biogeochemical Cycles, 3: 241-65.

Vörösmarty, C.J. and Moore, B., 1991. Modeling basin-scale hydrology in support of physical climate and global biogeochemical studies: An example using the Zambezi River. Studies in Geophysics, 12: 271-311.

Vörösmarty, C.J., Willmott, C.J., Choudhury, B.J., Schloss, A.L., Stearns, T.K., Robeson, S.M. and Dorman, T.J., 1996. Analyzing the discharge regime of a large tropical river through remote sensing, ground-based climatic data, and modeling. Water Resour. Res., 32: 3137-50.

Vörösmarty, C. J., C. A. Federer and A. L. Schloss, 1998. Potential evaporation functions compared on US watersheds: Possible implications for global-scale water balance and terrestrial ecosystem modeling, Journal of Hydrology 207: 147-169.

Potential evapotranspiration functions and their required inputs:

For detailed information, see Federer et al. (1996) and Vorosmarty et al. (1998).

PET References:

Federer, C.A., Vörösmarty, C.J. and Fekete, B., 1996. Intercomparison of methods for potential evapotranspiration in regional or global water balance models. Water Resour. Res., 32:2315-21.

Hamon, W. R., 1963. Computation of direct runoff amounts from storm rainfall. International Association of Scientific Hydrology Publication 63:52-62.

Jensen, M.E. and Haise, H.R., 1963. Estimating evapotranspiration from solar radiation. J. of the Irrig. and Drainage Div. of the Amer. Soc. of Civil Eng., 89(IR4):15-41.

McNaughton, K.G. and Black, T.A., 1973. A study of evapotranspiration from a Douglas Fir forest using the energy balance approach. Water Resour. Res., 9:1579-1590.

Monteith, J.L. 1965. Evaporation and environment. In: The state and Movement of Water in Living Organisms. Proc. 19th Symposium of the Society of Experimental Biology. Cambridge University Press, Cambridge, UK, pp. 205-33.

Penman, H.L. 1948. Natural evaporation from open water, bare soil and grass. Proc. of the Royal Society of London, A. 193:120-146.

Priestley, C.H.B. and Taylor, R.J, 1972. On the assessment of surface heat flux and evaporation using large scale parameters. Monthly Weather Review, 100:81-92.

Shuttleworth, W.J. and Wallace, J.S., 1985. Evaporation from sparse crops: An energy combination theory. Quarterly J. Royal Meteorol. Soc., 111: 839-855.

Thornthwaite, C.W. 1948. An approach toward a rational classification of climate. Geographical Review, 38: 55-94.

Turc, L. 1961. Evaluation de besoins en eau d'irrigation, evapotranspiration potentielle. Annals of Agronomy, 12:13-49.

Data Providers:

C. Vörösmarty and Annette Schloss, Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, Morse Hall, University of New Hampshire, Durham, New Hampshire, USA. Ph: 603.862.1792, Fax: 603.862.0188, Email: annette.schloss@unh.edu.

Last Data Update:

2/29/2000

Last Doc. Updated:

8/16/2001

Doc. Updated By:

Denise Blaha

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