Abstract
The effect of the scale of vegetation parameter aggregation on modeled evapotranspiration pattern and rate is explored. Vegetation biomass, height and fractional coverage per model grid cell were the vegetation parameters used in this research to explore the effects. A spatially explicit hydrologic model was developed and calibrated for a catchment scale watershed (11.6 km²). The dominant vegetation type over the catchment was prairie grass. Distributed vegetation parameters were taken from vegetation indices developed from satellite remote sensing images of the study area. Aggregation of the vegetation parameters followed a subcatchment scheme. The model was executed for one growing season for each subcatchment aggregation scheme. Evapotranspiration pattern was correlated with a remotely sensed surface brightness temperature image to assess the scaling effects of parameter aggregation. Evapotranspiration rate averaged over the catchment was calibrated with measured values of latent heat flux for the unaggregated case. Catchment average evapotranspiration for each case of vegetation parameter aggregation was compared for effects with respect to scale of aggregation. The evapotranspiration occurring during times of soil moisture stress on the vegetation was assessed in terms of the scaling effects on the catchment average conductance stress function. The results from the model simulations for pattern and rate of evapotranspiration show the areal scale of approximately 0.2 km² was the maximum aggregation limit for vegetation parameter influence on the model processes. A metric of vegetation spatial structure, the semi-variogram, was calculated for the vegetation images used. The scale of meaningful spatial structure in the data was found by the semi-variogram method to be similar throughout the growing season to the modeling results. The results of this research have general implications for understanding the effects vegetation parameters will have on model behavior and selecting vegetation data with an appropriate scale of spatial variability.
Hoffpauir, Richard James (2001). The effects of vegetation parameter aggregation on modeled evapotranspiration. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2001 -THESIS -H63.