Global Hydrological Archive and Analysis System (GHAAS) Water Balance Model

The GHAAS (USA) 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 Vorosmarty 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 GHAAS (USA) 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
Vorosmarty et al. (1989, 1996) and Vorosmarty 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.
These data represent reference data.

This Collection contains 4 datasets which provide model predictions of
actual evapotranspiration and runoff using two model run scenarios for
rooting depth. A dataset for model prediction of potential
evapotranspiration is also included as well as a dataset for model
inputs. The model inputs dataset includes the following variables: %
sunshine, solar radiation (cal-cm2/day), precipitation (mm/mon), vapor
pressure (kPa), wind speed (m/s), temperature (min, max, mean, range)
(deg. C), root depth, elevation, soil texture, land cover, runoff
(mm/yr), dewpoint temperature (deg. C). Input data have been assembled
from many sources, see Vorosmarty et al. (1998) or Data Center URL for
more details.