Nat. Hazards Earth Syst. Sci. Discuss., https://doi.org/10.5194/nhess-2018-134 Manuscript under review for journal Nat. Hazards Earth Syst. Sci. Discussion started: 22 May 2018 c Author(s) 2018. CC BY 4.0 License. Reconstruction and simulation of an extreme flood event in the Lago Maggiore catchment in 1868 Peter Stucki1,2, Moritz Bandhauer1,2,a, Ulla Heikkilä3,b, Ole Rössler1,2, Massimiliano Zappa4, 4 Lucas Pfister2, Melanie Salvisberg1,5, Paul Froidevaux2,3, Olivia Martius1,2, Luca Panziera1,2,6, Stefan Brönnimann1,2 1Oeschger Centre for Climate Change Research, University of Bern, Bern, 3012, Switzerland 2Institute of Geography, University of Bern, Bern, 3012, Switzerland 8 3Meteotest, Bern, 3012, Switzerland 4Eidg. Forschungsanstalt WSL, Birmensdorf, 8903, Switzerland 5Institute of History, University of Bern, Bern, 3012, Switzerland 6MeteoSvizzera, Locarno Monti, 6605, Switzerland 12 anow at Schweizerische Energie-Stiftung SES, Zurich, 8005, Switzerland bnow at LogObject, Zurich, 8048, Switzerland 16 Correspondence to: Peter Stucki (
[email protected]) Abstract. Heavy precipitation on the south side of the central Alps produced a catastrophic flood in October 1868. We assess the damage and societal impacts, as well as the atmospheric and hydrological drivers using documentary evidence, observations, and novel numerical weather and runoff simulations. 20 The greatest damage was concentrated close to the Alpine divide and Lago Maggiore. An atmospheric reanalysis emphasizes the repeated occurrence of streamers of high potential vorticity as precursors of heavy precipitation. Dynamical downscaling indicates high freezing levels (4000 m a.s.l.), extreme precipitation rates (max. 270 mm/24 h), and weather dynamics that agree well with observed precipitation and damage, and with existing 24 concepts of forced low-level convergence, mid-level uplift and iterative northeastward propagation of convective cells.