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Title: MODELING SOIL MOISTURE AND SURFACE FLUX VARIABILITY WITH AN UNTUNED LAND SURFACE SCHEME: A CASE STUDY FROM THE SOUTHERN GREAT PLAINS 1997 HYDROLOGY EXPERIMENT

Author
item MOHR, KAREN - UNIVERSITY OF TEXAS
item FAMIGLIETTI, JAMES - UNIVERSITY OF TEXAS
item BOONE, AARON - NAT. CENT. METEOR. RES.
item Starks, Patrick

Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) model was used in a case study of a 2,500 square kilometer area in southwestern Oklahoma 9-16 July 1997. The research objective was to assess PLACE's ability to simulate the spatial distribution and temporal variation of soil moisture and heat fluxes without model adjustment. Understanding PLACE's performance under these conditions provides insight to results from more complex land-atmosphere models using similar land surface schemes in data-poor environments. Model simulations used simple soil moisture and temperature measurements and standard meteorological observations. The model equations and parameters were not adjusted or tuned to improve model results. That is, the model and data were used "as is". Model results showed that the most accurate simulations occurred during the 48 hour periods immediately following heavy rainfall events, and that spatial distribution of soil moisture was strongly controlled by soil texture. Simple model initialization schemes coupled with modeled rainfall estimations could account for simulation output errors greater than 5 percent. Under dry conditions it is expected that models like PLACE, which use similar simple initialization, would also demonstrate a strong soil texture control on soil moisture.

Technical Abstract: The Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) model was used in a case study of a 2,500 square kilometer area in southwestern Oklahoma 9-16 July 1997. The research objective was to assess PLACE's simulation of the spatial variability and temporal evolution of soil moisture and heat fluxes without model tuning. Understanding PLACE's performance under these conditions may provide perspective on results from more complex coupled land-atmosphere simulations involving similar land surface schemes in data-poor environments. Model simulations were initialized with simple initial soil moisture and temperature profiles tied to soil type and forced by standard meteorological observations. The model equations and parameters were not adjusted or tuned to improve model results. The most accurate simulation of 5- and 10- centimeter soil temperature, fluxes of sensible and latent heat and soil moisture occurred during the 48 hour period following a heavy rainfall on July 11 and 15. The spatial pattern of soil moisture was strongly controlled by soil texture. Simplifications of the sub-surface soil moisture, soil texture and vegetation cover initialization schemes coupled with the uncertainty in the rainfall input data could account for differences in soil moisture greater than 5 percent. It is also likely that the soil thermal conductivity scheme in PLACE dampened the model's response to atmosheric demand after July 13, resulting in reduced evapotranspiration and warmer but slower drying soils. Under dry conditions, it is expected that models like PLACE using similar simple initialization would also demonstrate a strong soil texture control on soil moisture and surface fluxes and reduced spatial variability.