The Global Soil Wetness Project (GSWP) is an ongoing land surface modeling
activity of the International Satellite Land-Surface Climatology Project (I
SLSCP), a part of the Global Energy and Water Cycle Experiment. The pilot p
hase of GSWP deals with the production of a two-year global dataset of soil
moisture, temperature, runoff, and surface fluxes by integrating uncoupled
land surface schemes (LSSs) using externally specified surface forcings fr
om observations and standardized soil and vegetation distributions. Approxi
mately one dozen participating LSS groups in five nations have taken the co
mmon ISLSCP forcing data to drive their state-of-the-art models over the 19
87-88 period to generate global datasets. Many of the LSS groups have perfo
rmed specific sensitivity studies, which are intended to evaluate the impac
t of uncertainties in model parameters and forcing fields on simulation of
the surface water and energy balances. A validation effort exists to compar
e the global products to other forms of estimation and measurement, either
directly (by comparison to field studies or soil moisture measuring network
s) or indirectly (e.g., use of modeled runoff to drive river routing scheme
s for comparison to streamflow data). The soil wetness data produced are al
so being tested within general circulation models to evaluate their quality
and their impact on seasonal to interannual climate simulations. An Inter-
Comparison Center has also been established for evaluating and comparing da
ta from the different LSSs. Comparison among the model results is used to a
ssess the uncertainty in estimates of surface components of the moisture an
d energy balances at large scales and as a quality check on the model produ
cts themselves.