Applying WSR-88 Radar Rainfall on Short Time Scales to Hydrological Modeling of a Small Basin in Florida

The Black Creek Basin in North Florida has experienced flash flooding in 1992, 1996, 1997 and 1998, with flood damage to property exceeding $2 million and a Local State of Emergency declared in 1997.

NEXRAD-derived rainfall rates at 4 x 4 km resolution are applied to the Systeme Hydrologique Europeen distributed hydrological model (Mike-SHE) to investigate the comparative operational diagnostic advantages of using fully distributed (NEXRAD)- or Thiessen (gauge)-derived rainfall rates over this small (1253 km2) basin of modest topography during both convective and synoptic conditions. The results are relevant to the use of NEXRAD rain-rates and Thiessen-Polygon rainfall for small basins on monthly time scales. Model discharges using hourly Thiessen Polygon and NEXRAD rainfall rates are compared to observed discharge at two USGS gauging stations in the basin for January and July 1998. With all model parameters and initializations the same for both types of rainfall inputs, the results indicate significant differences in the calculated flows. An analysis of differences in results shows a distinct advantage of using NEXRAD rain rates in that a much greater understanding of model behavior and basin response is possible when using fully distributed rainfall inputs as opposed to the less discrete Thiessen inputs, even over such a small basin. On these time and space scales, the Thiessen method can introduce spurious runoff at the river gauges under convective conditions.