The Second Global Soil Wetness Project
Science and Implementation Plan
Paul Dirmeyer and Xiang Gao
Center for Ocean-Land-Atmosphere Studies, Calverton, Maryland, USA
Research Institute for Humanity and Nature, Kyoto, Japan
IGPO Publication No. 37
The Global Soil Wetness Project (GSWP) is an ongoing environmental
modeling research activity of the Global Land-Atmosphere System Study (GLASS)
and the International Satellite Land-Surface Climatology Project (ISLSCP),
both contributing projects of the Global Energy and Water Cycle Experiment
Its goals are to:
• Produce state-of-the-art global data sets of land surface
fluxes, state variables, and related hydrologic quantities.
• Develop and test large-scale validation, calibration, and assimilation techniques over land.
• Provide a large-scale validation and quality check of the ISLSCP data sets.
• Compare Land Surface Schemes (LSSs), and conduct sensitivity
studies of specific parameterizations and forcings, which should aid future
model and data set development.
GSWP-2 is closely linked to the ISLSCP Initiative II data
effort, and LSS simulations in GSWP-2 will encompass the same core 10-year
period as ISLSCP Initiative II (1986-1995).
There are five basic categories of participants in GSWP-2:
the operational centers, the land-surface modelers, validators of the model
output, those involved in remote sensing applications, and other users of
the model output. An Inter-Comparison Center will collect results from
participating models, perform consistency checks, and basic comparisons.
A major product of GSWP-2 will be a multi-model land surface
analysis for the ISLSCP Initiative II period. This will be a land surface
analog to the atmospheric reanalyses, and will include estimates of uncertainties
based on inter-model spread. The science plan also includes in situ
validation with data from field campaigns, observational networks and long-term
monitoring sites. Modeling sensitivity studies will involve re-integrating
the LSSs over part or all of the global, 10-year domain to test the response
of the models to changes in meteorological data (including choice of reanalysis
products, impacts of bias correction, sensitivity to the range in observational
estimates, and impacts of rain-gauge under-catch) and surface parameters.
Comparisons to land models of simple and intermediate complexity will also
A new thrust for GSWP-2 is a stronger connection to applications
in remote sensing. In addition to the classical attempts to validate
the typical land-surface state variables using satellite retrievals, GSWP-2
also intends to expand the validation and assimilation capabilities of current
LSSs. This is to be done by the development of algorithms by which
LSSs can directly report brightness temperatures, like those sensed by instruments
All data sets will conform to the Assistance for Land-surface
Modeling Activities (ALMA) standards set forth within GLASS. New Internet
data server technologies will be used to distribute and analyze data, reducing
archiving and data management burdens on participants.