Effects of Spatial Variability and Scale on Areally Averaged Evapotranspiration

This paper explores the effects of spatial variability and scale on areally averaged evapotranspiration. A spatially distributed water and energy balance model is employed to determine the effect of explicit patterns of land surface characteristics and atmospheric forcing on areally averaged evapotranspiration over a range of increasing spatial scales. The analysis is performed from the local scale to the catchment scale. The study area is King's Creek catchment, an 11.7 km2 watershed located on the native tallgrass prairie of Kansas. It is shown that a threshold scale, or representative elementary area (REA) exists for evapotranspiration modeling. It is shown further that the dominant controls on the scaling behavior of catchment-average evapotranspiration, and thus the size of the REA, depend on the dominant controls on its components (bare-soil evaporation, wet canopy evaporation, and dry canopy transpiration) and whether evapotranspiration is occurring at potential rates or soil- and vegetation-controlled rates. The existence of an REA for evapotranspiration modeling suggests that in catchment areas smaller than this threshold scale, actual patterns of model parameters and inputs may be important factors governing catchment-scale evapotranspiration rates in hydrological models. In models applied at scales greater than the REA scale, spatial patterns of dominant process controls can be represented by their statistical distribution functions. It appears that some of our findings are fairly general and will therefore provide a framework for understanding the scaling behavior of areally averaged evapotranspiration at the catchment and larger scales. Our results may have further implications for representing subgrid-scale land surface heterogeneity in hydrological parameterizations for atmospheric models.

[1]  J. Famiglietti,et al.  Multiscale modeling of spatially variable water and energy balance processes , 1994 .

[2]  Keith Beven,et al.  On hydrologic similarity: 2. A scaled model of storm runoff production , 1987 .

[3]  J. Stewart,et al.  Spatial variability of evaporation derived from aircraft and ground‐based data , 1992 .

[4]  Keith Beven,et al.  Effects of spatial variability and scale with implications to hydrologic modeling , 1988 .

[5]  Murugesu Sivapalan,et al.  Scale issues in hydrological modelling: A review , 1995 .

[6]  Keith Beven,et al.  Runoff Production and Flood Frequency in Catchments of Order n: An Alternative Approach , 1986 .

[7]  Alan K. Knapp,et al.  Physiological Interactions Along Resource Gradients in a Tallgrass Prairie , 1991 .

[8]  P. Sellers,et al.  The First ISLSCP Field Experiment (FIFE) , 1988 .

[9]  G. Jedlovec,et al.  Variability of geophysical parameters from aircraft radiance measurements for FIFE , 1992 .

[10]  Eric F. Wood,et al.  On Hydrologic Similarity: 1. Derivation of the Dimensionless Flood Frequency Curve , 1986 .

[11]  Piers J. Sellers,et al.  The first International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment - FIFE , 1992 .

[12]  Murugesu Sivapalan,et al.  ON THE REPRESENTATIVE ELEMENTARY AREA (REA) CONCEPT AND ITS UTILITY FOR DISTRIBUTED RAINFALL-RUNOFF MODELLING , 1995 .

[13]  Keith Beven,et al.  On hydrologic similarity: 3. A dimensionless flood frequency model using a generalized geomorphologic unit hydrograph and partial area runoff generation , 1990 .

[14]  Murugesu Sivapalan,et al.  Investigating the representative elementary area concept: An approach based on field data , 1995 .

[15]  T. Schmugge,et al.  Results from the Push Broom Microwave Radiometer flights over the Konza Prairie in 1985 , 1988 .

[16]  Eric F. Wood,et al.  Application of multiscale water and energy balance models on a tallgrass prairie , 1994 .

[17]  James C. I. Dooge,et al.  Looking for hydrologic laws , 1986 .

[18]  K. Beven,et al.  Similarity and scale in catchment storm response , 1990 .