Localized flood forecasting ACT A dual-polarization X-band radar supplied by EWR Radar Systems is helping researchers in Missouri better monitor intense rainfall in the Hinkson Creek Neil I Fox, Christopher A Steward and Noel Aloysius, School of Natural Resources, University of Missouri local T he need to forecast streamflow and flooding has been a driver in the development of weather radar for decades. Radar has the ability to estimate rainfall amounts over wide areas at regular, short intervals of time, and this makes it an attractive tool for hydrologists who want to improve predictions of streamflow and floods. However, the ability of hydrological models to effectively use rainfall data from radars depends on the quality of that data. Furthermore, for small catchments, the proximity of the radar can be paramount. The closer a radar is to the catchment in question, the higher the spatial resolution of the data and the closer the 250 radar beam is to the surface. The lower beam altitude helps reduce errors caused by 200 changes in the precipitation as it falls from aloft. In theory, a small locally sited radar should be able to do 150 better than a larger, more distant one when it comes to hydrological applications. 100 Flow values ABOVE: Figure 1: The MZZU radar BELOW: Figure 4: Hydrograph with SWAT model output for the Hinkson Creek flood of June 25, 2021. The graph shows simulated flow using data from rain gauges (orange line), MRMS (green line), and three MZZU radar rainfall algorithms (red, purple and brown lines), as well as the Hinkson USGS stream gauge observation (dashed blue line) hydrological prediction using data from the MZZU X-band dual-polarization weather radar (Figure 1) as input into a hydrological model of the Hinkson Creek, which runs through the city of Columbia, Missouri. The Hinkson Creek catchment (shown in Figure 2) has an area of 228km 2 and falls about 140m in elevation from the headwaters in the northwest to the more urbanized area in the southwest. The landscape is evenly divided between pasture and cropland, forest and urban cover, making it an interesting and complex watershed to study. The radar, an E800 dual-polarization X-band radar supplied by EWR Radar Systems, is situated just outside the southeast corner of the watershed. Rainfall fields from the MZZU radar are quality controlled using in-house processing that exploits the dual-polarization measurements to provide corrections for range and attenuation. Rainfall rates derived from three variations of the processing algorithm of the MZZU data were used as input to the Soil Water Assessment Tool (SWAT) hydrological model of the catchment. This model allows rainfall amounts to be entered for each of 30 subcatchments, making the representation of small pockets of heavy rain valuable to the model’s operation. For comparison, inputs from quantitative precipitation estimates (QPE) from the Multi-Radar/Multi-Sensor (MRMS) system operated by the National Hinkson gauge Gauge four-hourly MRMS MZZU Rp1 (KDP, D) MZZU Rp2 (KDP, D) MZZU Rp3 (KDP, D) To test this theory, a research team at the University of Missouri set out to investigate the effectiveness of a small gap-filling radar on Studying the Hinkson Creek watershed 50 23 June 2021 24 25 Month and year 26 44 • www.meteorologicaltechnologyinternational.com • April 2024