Rainfall extremes observed by a weather radar in the northern tropical Andes

We characterize seasonal and diurnal spatiotemporal features of extreme rainfall in a 45,000 km 2 area within the tropical Andes of northern South America. We validate radar-based quantitative precipitation estimates for extreme rainfall using in-situ observations, finding a strong spatiotemporal coherence between the datasets through methods based on correlations, timing, and probability mass functions. We then explore the seasonal and diurnal cycles of extreme rainfall, focusing on the local atmospheric environments associated with these extremes. Results show that rainfall extremes in the region (percentile 99.5) exhibit intensities of more than 27 times the average, while the strongest events may reach intensities of up to 85 times the average. Moreover, our findings reveal a consistent timing of extreme precipitation events, occurring between 15:00 and 22:00 LST, accounting at this time range for more than 3% of all seasonal rainfall accumulation. We show that the traditional approach of analyzing seasonal 10-year average rainfall might leave out the high spatiotemporal variability of extreme events. By focusing on a specific threshold and the most intense rainfall events, we identify two main spatiotemporal patterns of extreme rainfall based on the magnitude and the ratio between maxima and mean rain rate. Moreover, these patterns are driven by the interplay of regional atmospheric mechanisms and orographic features. This research improves our understanding about the spatiotemporal characteristics of rainfall extremes and their relationship with atmospheric and orographic factors. It uses high-resolution weather radar data to provide valuable insights for diagnosing, understanding, and modeling extreme rainfall in tropical regions. Graphical overview of the main features of extreme rainfall in tropical northern Andes. (a) CHIRPS’ precipitation 99.5 percentile (mm day − 1 ) for the period 2013-2022 in the northern Andes with the location of radar coverage area highlighted in dashed-red line. (b) Percentile 99.5 of quantitative precipitation estimates – QPE – from weather radar data (mm h − 1 ). Schematics of relevant seasonal dynamic patterns related to extreme rainfall in the region during (c) MAM and (d) JJA. Red and dark blue arrows are for seasonal differences (extreme events minus mean state) in low-level wind, with color indicating a decrease (red) or increase (blue) in specific humidity (SH) . Light cyan tailed arrows represent wind at middle levels (500 hPa) and positive seasonal differences of SH , while dark cyan arrows represent wind differences and increases in SH at the same level. Indicative locations of the maxima of P99.5 and P99.5 relative to the mean are also included. • Extreme rainfall patterns differ in long-term averages and relative to the mean rain rate. • Extreme events may contribute over 3% of total seasonal rainfall. • Regional atmospheric environments only partially explain the physical mechanisms of extreme rainfall.