Rainfall in Florida is very dynamic in nature and is the greatest determining factor in hydrologic modeling studies. These studies traditionally have used gauge-only rainfall estimates despite their limitations and the advances in multi-sensor precipitation estimates. The convenience and familiarity with gauge data are a major factor leading to their continued use; however, there also have been questions about the statistical consistency and quality of radar-derived precipitation data.

We previously reported on an intercomparison between gauge-only Thiessen polygon data with the gridded 4 × 4 km Florida State University (FSU) version of the National Weather Service (NWS) Multi-sensor Precipitation Estimator (MPE) scheme over several Florida basins. We showed that rain gauge density within a basin is highly correlated with the magnitude of rainfall differences between the two datasets. The study also showed that seasonal characteristics of rainfall are an important factor leading to differences. The current paper evaluates the impacts of these input differences on streamflow by using a specialized, fully-distributed hydrologic model—the Watershed Assessment Model (WAM). Although WAM can model various water quality parameters, we focus on the streamflow produced by the different rainfall inputs. By describing differences in streamflow, we provide results that modelers can easily relate to--the impact of higher-resolution MPE rainfall data on their model's bottom-line.

We have modeled the Suwannee River basin in North Florida between 1996 and 2005. Hourly rain gauge data used as input to the FSU MPE scheme were obtained from the National Climatic Data Center (NCDC) and the Suwannee River Water Management District (SRWMD). This combination provides the most reliably-dense gauge network possible. All of the rain gauge data were quality-controlled by FSU. Quality-controlled radar data were obtained from the NWS's Southeast River Forecast Center (SERFC). The FSU 4 × 4 km MPE dataset was developed through years of collaboration between Florida State University, the Florida Department of Environmental Protection (FDEP), and the National Weather Service. Its characteristics have been described in our previous publications.

This paper will compare simulated flows using the gridded FSU MPE rainfall inputs with simulated flows using gauge-only Thiessen polygon rainfall inputs. Both versions of simulated flow also are compared to measured streamflow observations. The Suwannee River basin contains abundant streamflow data, allowing comparisons to be made at various points within the basin. This allows us to determine how streamflow at different locations in the basin responds to rainfall scenarios that vary from intense and isolated to widespread and light. Rain gauge density in the SRWMD has progressively increased by more than five times during the past 10 years. Our paper also will describe the impact of rain gauge density on the quality of simulated streamflow. Finally, the paper will describe possible thresholds of gauge density, as well as the pros and cons encountered in modeling with the two distinctly different rainfall inputs.