Adjustment of the Z-R Relationship in Real-Time for Use in South Florida

Due to the limitations of rain gauges in representing spatial rainfall variability, radar estimates are of particular importance, especially in areas subject to variable rainfall from convective storms. This study explores the use of a real-time adjustment of the reflectivity-rainfall (Z-R) relationship in determining radar rainfall estimates throughout the South Florida Water Management District (SFWMD). Level II reflectivity data from the Melbourne (KMLB) NEXRAD radar site, operated by the National Weather Service (NWS), was used in conjunction with 15-minute precipitation data from real-time gauges operated by the SFWMD. The coefficients A and b of the Z-R relationship were adjusted at each time step of the study period, based on gauge and reflectivity pairs obtained from the preceding 24 hours, allowing for variability within the Z-R relationship as the rainfall event progressed. Verification of the radar estimates was conducted with a separate set of rain gauges, not included in the estimation of A and b, using various graphical and statistical methods. To further explore the applicability of this study to the SFWMD, radar estimates currently being supplied to the District by means of a different algorithm were also verified with the same methods for comparison to the real-time adjusted estimates.