In recent years, the frequency and intensity of extreme rainfall has substantially increased in most regions of Germany. In addition, periods from several days to weeks with an exceptional high number of quasi-stationary thunderstorms related to atmospheric blocking and causing locally extreme precipitation accumulations have been observed (cf. May/June 2016 and 2018; Piper et al., 2016; Mohr et al., 2020). At the same time, the frequency and duration of dry weather and low water discharge periods changes dilution and transport capacities of entire river networks. As a consequence, urban flash floods and related damage to infrastructures and water pollution from untreated sewage discharges increase significantly, making appropriate adaptation strategies indispensable.

The sub-project “Urban flash floods and sewerage” of Helmholtz-Initiative Climate Adaptation and Mitigation: two Sides of the same Coin (HI-CAM) aims to simulate and assess the entire effect chain: from extreme rainfall scenarios including expected changes and temporal clustering through inundation and flooding to resulting infrastructure damage to the effect of rainwater overflow to the impacts on water quality and ecology. The frequency and intensity of extreme convective rainfall in an urban area is statistically evaluated based on station and radar data. Focus will be on quasi-stationary convective cells locally producing largest rainfall accumulations. Spatial shifting of extreme rainfall patterns to the region of interest allows to estimate upper bounds of the extremes. Probabilistic precipitation changes for future periods will be quantified from an ensemble of high-resolution RCM. To better understand the temporal variability of the local-scale extremes, we will also investigate their relation to large-scale dynamics in terms of atmospheric blocking (Mohr et al., 2019) or teleconnections (Piper and Kunz, 2017) influencing serial clustering over periods of days to weeks, and how these conditions will change in the future.

HI-CAM builds upon the three pillars:

1. Climate adaption: using science-based scenarios to support a mitigation strategy leading to a carbon-neutral Germany in 2050;

2. Climate mitigation: to develop appropriate adaptation to extremes options; and

3. Communication: to develop coherent communication strategies and campaigns.

References:

Mohr, S., Wandel, J., Lenggenhager, S., und Martius, O. (2019): Relationship between blocking and warm season thunderstorms in western and central Europe. Q. J. R. Meteor. Soc., 145 (724), 3040–3056, doi:10.1002/qj.3603.

Mohr, S., Wilhelm, J., Wandel, J., Kunz, M., Portmann, R., Punge, H. J., Schmidberger, M. und Grams, C. (2020): The role of large-scale dynamics in an exceptional sequence of severe thunderstorms in Europe May/June 2018. Weather Clim. Dynam. Discuss., doi:10.10.5194/wcd-2020-1.

Piper D., M. Kunz, F. Ehmele, S. Mohr, B. Mühr, A. Kron and J. Daniell (2016): Exceptional sequence of severe thunderstorms and related flash floods in May and June 2016 in Germany. Part I: Meteorological background Nat. Hazards Earth Syst. Sci. Nat. Hazards Earth Syst. Sci., 16, 2835–2850.

Piper, D. and Kunz, M. (2017): Spatiotemporal variability of lightning activity in Europe and the relation to the North Atlantic Oscillation teleconnection pattern, Nat. Hazards Earth Syst. Sci., 17, 1319–1336, doi:10.5194/nhess-17-1319-2017.

Piper, D., Kunz, M., Allen, J. T., and Mohr, S. (2019): Investigation of the temporal variability of thunderstorms in Central and Western Europe and the relation to large-scale flow and teleconnection patterns. Q. J. R. Meteor. Soc., 145 (725), 3644–3666, doi:10.1002/qj.3647.