A multiscale study of a heavy rainfall event of April 2019 in Rio de Janeiro city

Abstract On April 8th and 9th, 2019, the city of Rio de Janeiro experienced intense rainfall characterized by accumulations exceeding 300 mm/24 hours, reaching a maximum of 343.4 mm. Accumulations were higher in stations located south of the Tijuca Massif, while lower values were recorded in the Northern Zone (NZ) stations. The rainfall persisted for 28 h, and three distinct precipitation peaks denoted as P1, P2, and P3, were identified. The P1 stood out for its higher intensities and long-lived rainfall duration and was the only peak associated with electrical discharges. It exhibited clouds with the highest tops, lowest temperatures, and a prevalence of clouds with ice-phase tops. P1 was associated with the presence of Cumulonimbus clouds, hitting significantly all stations in the Southern Zone. P2 and P3 were similar in intensity and duration, although with distinct cloud characteristics. P3 was dominated by Nimbostratus clouds, having the lowest top heights and warmer temperatures, and a prevalence of supercooled water at the cloud tops, indicating a high liquid water content. P2 was intermediate, featuring cloud tops lower than P1 but higher than P3. However, during peak rainfall intensity, Nimbostratus clouds were present, which was more critical in NZ stations, when surface winds were predominantly from the North. The event was influenced by the transport of high moisture content from the Central-Western region of Brazil towards the Southeast, coupled with the formation of a cyclone near the coast of Rio de Janeiro, besides the presence of pronounced moisture convergence zones over the municipality.