An intercomparison of soil moisture fields in the North American Land Data Assimilation System (NLDAS)

[1] The multiple-agency/university North American Land Data Assimilation System (NLDAS) project is designed to provide enhanced soil and temperature initial conditions for numerical weather/climate prediction models. Currently, four land surface models (LSMs) are running in NLDAS both in retrospective mode and in real-time mode. All LSMs are driven by the same meteorologic forcing data and are initiated at the same time with the same relative soil wetness. This study intercompares these NLDAS soil moisture fields with each other and with available observations. The total water storage and the storage variability range are the foci of the study. The mean statistical properties and the spatial variation of these soil moisture fields along with their temporal change are investigated. Model soil moisture fields are compared to soil moisture observations in Illinois. The storage variability range in Arkansas-Red River basin is validated against a water balance diagnostic analysis using historical precipitation and streamflow data. There is better agreement between observed and simulated ranges of water storage variability than between observed and simulated amounts of total water storage. Significant differences are found between NLDAS-simulated soil moisture fields from the different models. Total water storage is found to be highly model dependent. There is better agreement between models in the water total water storage range than in the model values of total water storage. Total water storage ranges agree best in humid areas where variation in water storage is strongly driven by variation in precipitation. In very dry areas, agreement between simulated water storage ranges is weak because model differences have as much influence on water storage range as climate variability in these areas. Finally, the spin-up properties of the models and relationships between water storage properties and climate are investigated. The results of this study should provide important insights into the similarities and differences of the four LSMs in NLDAS. Differences in NLDAS soil moisture fields pose challenges to land surface modelers who intend to use soil moisture field from one model to initialize another model.

[1]  R. Vogel,et al.  Annual hydroclimatology of the United States , 2000 .

[2]  W. Collins,et al.  The NCEP–NCAR 50-Year Reanalysis: Monthly Means CD-ROM and Documentation , 2001 .

[3]  J. Schaake,et al.  Total water storage in the Arkansas-Red River basin , 2003 .

[4]  J. D. Tarpley,et al.  Real‐time and retrospective forcing in the North American Land Data Assimilation System (NLDAS) project , 2003 .

[5]  Douglas A. Miller,et al.  A Conterminous United States Multilayer Soil Characteristics Dataset for Regional Climate and Hydrology Modeling , 1998 .

[6]  C. Daly,et al.  A Statistical-Topographic Model for Mapping Climatological Precipitation over Mountainous Terrain , 1994 .

[7]  A. Dalcher,et al.  A Simple Biosphere Model (SIB) for Use within General Circulation Models , 1986 .

[8]  J. D. Tarpley,et al.  Land surface model spin‐up behavior in the North American Land Data Assimilation System (NLDAS) , 2003 .

[9]  D. Lettenmaier,et al.  Streamflow simulation for continental‐scale river basins , 1997 .

[10]  D. Lettenmaier,et al.  A simple hydrologically based model of land surface water and energy fluxes for general circulation models , 1994 .

[11]  J. D. Tarpley,et al.  The multi‐institution North American Land Data Assimilation System (NLDAS): Utilizing multiple GCIP products and partners in a continental distributed hydrological modeling system , 2004 .

[12]  Y. Xue,et al.  Modeling of land surface evaporation by four schemes and comparison with FIFE observations , 1996 .

[13]  Randal D. Koster,et al.  The Interplay between Transpiration and Runoff Formulations in Land Surface Schemes Used with Atmospheric Models , 1997 .