Heavy rains in Brno Region (The Czech Republic)

This study evaluates occurrence of the heavy rains at urban areas on the example of Brno agglomeration. Extreme precipitation events are studied with the help of 1-minute records from three urban sites in the Brno and one site in the rural region. Additionally data from nine Hellmann rain gauges from Brno and surroundings were used. The event of torrential rains was evaluated according to Wussow’s method. The study found that torrential rains occurred in Brno in the season from April to November. The fifteen-year long observation of the phenomenon at Brno-Žabovřesky station shows varying frequency of torrential rainfall - from none in 2007 to four in 2004 and 2010. The most extremal was catastrophic downpour on July 15, 2009 when precipitation sum reached total up to 42.7 mm in 52 minutes and the maximal rainfall intensity was 4.1 mm/min. This phenomenon occurs only one day after downpour on July 14, 2009. The overall number of torrential episodes is not very high, but it is compensated by the fact that they can repeat in a relatively short period of time, due to specific synoptic conditions. Maximum rainfall intensity during torrential rains reaches values of about 3 mm / min and the average proportion of torrential rain in the daily precipitation sum is around 70%. The phenomenon of heavy rains represents a significant problem for densely populated urban areas because such extreme rainfall has a large impact on the hydrological system of cities.