Validation of NEXRAD DSP product with high accuracy rain gauges network

A network of 50 rain gauges in the Upper Guadalupe River Basin were used to compare with NEXRAD's Digital Storm Total Precipitation (DSP) rainfall estimates from two radars, the KEWX radar at New Braunfels, Texas and the KDFX radar at Laughlin Air Force Base near Del Rio, Texas, for the period from September 2006 to May 2007. The rainfall data comparisons were examined based on different time scales: 6 minutes, 30 minutes, one hour, and storm total, different distances from radar to gauges (from near range, middle range to far range), and different gauge elevations from 200 m to 700 m. Results show a strong range dependence for both radar estimates. In the 6 minutes, 30 minutes, and one hour scales, the KEWX radar underestimated in the near range (< 50 km) and far range (>150 km), while overestimated in the middle range (50-150 km). The KDFX radar underestimated rainfall for all distances larger than 160 Km, and then overestimated rainfall in the range of 100-160 km. At the storm total time scale the DSP product offers a good rainfall estimation and detection, the correlation with rain gauges is the highest (KEWX R² = 0.59 and KDFX R² = 0.37); the mean relative differences between gauges observations and radars estimates are the lowest (52% for the KEWX and 59% for the KDFX). The probability of rain detection (POD) is 92% for the KEWX radar and 85% for the KDFX radar at the storm scale, which are higher than the rain gauges PODs of 84% and 79%, respectively, while the radar PODs are less than gauges in the 6 minutes, 30 minutes and hour time scales. The reason for this is not very clear and needs further investigation. We suggest a more detailed study of the DSP products, for longer periods and for different climatic and topographic settings.