The Second Global Soil Wetness Project
Science and Implementation Plan

Compiled by:
Paul Dirmeyer and Xiang Gao
Center for Ocean-Land-Atmosphere Studies, Calverton, Maryland, USA

Taikan Oki
Research Institute for Humanity and Nature, Kyoto, Japan

December 2002
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 (GEWEX).
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 be conducted.

    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 in orbit. 

    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.