Short-duration precipitation extremes detected by the DWD radar network and associated circulation patterns

Increasing concentration of water vapour in the Earth’s atmosphere being a result of continued global warming has a pronounced impact on precipitation patterns. Particularly affected are precipitation extremes, which are expected to intensify at a rate of 6-7% per each 1°C of air temperature warming following the Clausius-Clapeyron (CC) relation. However, many regional studies have shown that the CC rate is appropriate for long-duration precipitation extremes (LDPEs; multi-daily to daily extremes) rather than for short-duration precipitation extremes (SDPEs; sub-daily to hourly extremes). SDPEs are projected to intensify even twice as fast as expected from the CC relation posing substantial risk on human and natural systems. Yet over the years, SDPEs have received much less scientific attention than LDPEs, mainly due to the limitations of measurement systems. Our aim to provide insight into behaviour of SDPEs detected by the radar network of Deutscher Wetterdienst (DWD) from 2001 to 2020 by exploring their temporal and spatial variability as well as links to circulation patterns.

The study is based on the Catalogues of Radar-based heavy Rainfall Events (CatRaRE), which have been generated using reprocessed gauge-adjusted data of the DWD radar network known as RADKLIM (Lengfeld et al. 2021). The links between the precipitation extremes and circulation patterns have been quantified by applying two circulation type classifications developed by James (2019). Both of them are related to the Hess-Brezowsky Grosswetterlagen.

The results have demonstrated that SDPEs are common phenomena occurring most frequently in the afternoon hours of the summer season. They are, however, characterised by relatively small size occurring on a local rather than a regional scale – the median area of SDPEs reaches up to 24 km², while the median area of LDPEs reaches up to 184 km², as a results, SDPEs often cannot be captured by rain gauge station network. The circulation patterns favouring SDPEs can be divided into two groups. The first group constitute circulation patterns commonly known as those favorable for precipitation, such as cut-off lows and cyclonic circulation patterns. The second group constitute, in turn, anticyclonic meridional or mixed circulation patterns, frequently accompanied by southerly airflow. In the summer, these circulation patterns are capable of inducing high thermal instability and development of small-scale, isolated convective cells. As the convective structures are difficult to detect by rain gauge stations, the role of some circulation patterns in shaping the precipitation extremes seems to be underestimated in the previous studies.

James P, 2019, Extended Grosswetterlagen: A new synoptic type classification for Central Europe accounting for both circulation and air mass characteristics, EMS Annual Meeting Abstracts, 16.
Lengfeld K, Walawender E, Winterrath T, Weigl E, Becker A, 2021, Heavy precipitation events Version 2021.01 exceeding return period of 5 years from RADKLIM-RW Version 2017.002. doi:10.5676/DWD/CatRaRE_T5_Eta_v2021.01.