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Description:
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Spatial variability of rainfall is a significant factor in hydrologic and water
quality modeling . In recent years , characterizing and analyzing the effect of spatial
variability of rainfall in hydrologic applications has become vital with the advent of
remotely sensed precipitation estimates that have high spatial resolution . In this study ,
the effect of spatial variability of rainfall in hourly runoff generation was analyzed using
the Soil and Water Assessment Tool (SWAT ) for Big Sandy Creek and Walnut Creek
Watersheds in North Central Texas . The area of the study catchments was 808 km2 and
196 km2 for Big Sandy Creek and Walnut Creek Watersheds respectively . Hourly
rainfall measurements obtained from raingauges and weather radars were used to
estimate runoff for the years 1999 to 2003 . Results from the study indicated that
generated runoff from SWAT showed enormous volume bias when compared against
observed runoff . The magnitude of bias increased as the area of the watershed increased
and the spatial variability of rainfall diminished . Regardless of high spatial variability ,
rainfall estimates from weather radars resulted in increased volume of simulated runoff .
Therefore , weather radar estimates were corrected for various systematic , range -dependent
biases using three different interpolation methods : Inverse Distance
Weighting (IDW ) , Spline , and Thiessen polygon . Runoff simulated using these bias adjusted radar rainfall estimates showed less volume bias compared to simulations using
uncorrected radar rainfall . In addition to spatial variability of rainfall , SWAT model
structures , such as overland flow , groundwater flow routing , and hourly
evapotranspiration distribution , played vital roles in the accuracy of simulated runoff . |