Reconstruction and simulation of an extreme flood event in the Lago Maggiore catchment in 1868

Abstract

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. 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 concepts of forced low-level convergence, mid-level uplift and iterative northeastward propagation of convective cells. Simulated and observed peak levels of Lago Maggiore differ by 2 m, possibly because the exact cross-section of the lake outflow is unknown. The extreme response of Lago Maggiore cannot be attributed to low forest cover. Nevertheless, such a paradigm was adopted by policy makers following the 1868 flood, and used to implement nationwide afforestation policies and hydraulic structures. These findings illustrate the potential of high-resolution, hydro-meteorological models – strongly supported by historical methods – to shed new light on weather events and their socio-economic implications in the 19th century.

Towards the Development of a Pan-European Stochastic Precipitation Dataset

“…Thus, precipitation associated with frontal systems can be better represented in comparison to precipitation gained by convective systems, which may be relevant for summer flooding. As an example, the Twentieth Century Reanalysis dataset (20CR) was dynamically downscaled with the Weather Research and Forecasting (WRF) model to investigate gustiness in Switzerland (Stucki et al, 2016) and the Lago Maggiore flood in 1868 (Stucki et al, 2018). While the timing and magnitude of the peak gusts are not well captured by the model, the simulated precipitation pattern agrees well with observations.…”

Historical weather data for climate risk assessment

“…It has been applied for a number of historical weather extremes including blizzards, flash floods, or storms. [139][140][141] Fortunato et al 142 used a suite of models to downscale a strong storm that hit the Iberian Peninsula in 1941, and to simulate water levels and inundated area in the Tagus estuary. Bresson et al 143 studied the 1952 North Sea storm surge using downscaling coupled with a wave model.…”