Radar cluttering incidence in the estimation of rainfall fields in the Colombian Andes

The spatial variability of rainfall is difficult to measure due to the lack of ground weather rain gauges. As a result, meteorological radars have become crucial sources of information for estimating precipitation fields. However, radar cluttering, which refers to external factors of nature that affect radar data quality, poses a significant challenge, and contributes to errors and uncertainties in the estimation process. In this study, we focused on analyzing the impact of cluttering on the Barrancabermeja C-band weather radar, situated between the Eastern and Central Ranges in the Colombian Andes. The analysis was conducted using radar information collected between 2019 and 2020. A frequency analysis of reflectivity of rainless day records showed the topographic interferences caused by the surrounding radar Ranges. Afterwards, the radar quality index (RQI) for both rainy and dry conditions was estimated considering factors such as clutter frequency map, partial beam blockage, effects of range distance quality, radar noise, and attenuation. The evaluation revealed an approximate clutter area of 50% in a beam elevation of 0.5°, primarily associated with the topographical interferences, indicating a direct impact of the Andean region on radar data quality.

Finally, we focused on intense rainfall events (greater than 10mm per event) to determine the parameters of three Quantitative Precipitation Estimation (QPE) relationships (Marshall & Palmer (1948), Seliga & Bringi (1976), and Sachidananda & Zrinc (1987) methodologies). Records from 91 available rain gauges were used to obtain relationships for individual gauges and, for four individual rings spaced 50 km from the radar. By employing these relationships, we calculated uncertainty maps of the quantitative precipitation estimation, obtaining an uncertainty of 60% from cluttering in the QPE of the meteorological radar. Overall, our findings emphasize the significant role of cluttering in the estimation of precipitation fields from the Barrancabermeja radar. The study underscores the importance of addressing cluttering effects and accounting for the topographical interferences in radar data interpretation to enhance the accuracy of quantitative precipitation estimates in the Andean region.