SPATIAL SCALE INFLUENCES ON MODELED RUNOFF FOR LARGE WATERSHEDS |
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| Authors: | M L Shelton |
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| Institution: | Department of Geography , University of California , Davis, California 95616 |
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| Abstract: | Modeling the runoff subsystem for large drainage basins requires simplification in representing natural processes owing to the spatial variability of mass and energy transfers in a watershed. Many models represent temporally and spatially distributed watershed variables by some form of aggregation or lumping. Scale becomes a factor in the lumping decision because some of the variables are spatially continuous while others are spatially discontinuous. The effects of scale differences on lumping in large watersheds is examined using the 27,300 km2 drainage area of the Deschutes River, Oregon. The watershed is modeled using three different spatial aggregations for representing the runoff subsystem. Agreement between modeled and observed monthly runoff for water years 1951-60 is analyzed to evaluate the magnitude of the difference between corresponding observed and modeled values. Increasing the number of spatial units in the model from 1 to 9 reduces all of the error terms by about 35 percent, but 20 spatial units in the model reduce the error terms by 50 percent or more. These data provide explicit evidence of improved modeling accuracy achieved by employing a disaggregated watershed model to represent spatially heterogeneous conditions in a large drainage basin. Key words: watershed modeling, scale, large watersheds, hydroclimate, Deschutes Basin.] |
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