Reforecasting the November 1994 flooding of Piedmont with a convection-permitting model
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Reforecasting the November 1994 flooding of Piedmont with a convection-permitting model Valerio Capecchi1 Received: 27 March 2020 / Accepted: 6 August 2020 / © Springer Nature Switzerland AG 2020
Abstract The Piedmont region in Italy was affected by a heavy rainfall event in November 1994. On the 4th convective cells involved the coastal mountains of the region. On the 5th and early 6th, there were abundant precipitations, related to orographic lift and low-level convergences, in the Alpine area. This study aims to evaluate whether a convection-permitting model provides more valuable information with respect to past numerical experiments. Results for the 4th of November show that the high-resolution model successfully reconstructs the structure of precipitation systems on the downstream side of the coastal mountains. As regards the precipitations of the 5th of November, no added value is found. However, we provide evidence of the anomalously intense transport of moist air from the tropical and subtropical Atlantic and postulate how such transport is responsible for reducing the stability of the flow impinging on the Alps. Keywords Convection-permitting model · Severe weather · Past events · Reforecast
1 Introduction Every year, weather-related disasters cause huge damage, significant economic losses and often casualties. According to the “Atlas of Mortality and Economic Losses from Weather, Climate and Water Extremes 1970-2012” edited by the World Meteorological Organization, floods and storms are the costliest events in Europe. Among such dramatic cases, the severe weather event of November 1994 in the Piedmont region (north-western Italy) is definitively one to be considered as remarkable. As a consequence of the heavy rainfall, several rivers in the southern part of the region flooded causing huge economic losses (estimated at about 14 billion US dollars) and 70 people died. Past numerical simulations were able to provide quite accurate reconstructions of the event. Nevertheless, the improvements achieved over the last 25 years in weather modelling pose the question of whether we can obtain new insights into the Piedmont flooding by using convective-scale numerical models. Valerio Capecchi
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LaMMA - Laboratorio di Meteorologia e Modellistica Ambientale per lo sviluppo sostenibile, Via Madonna del Piano 10, Sesto Fiorentino, Florence, Italy
Bulletin of Atmospheric Science and Technology
Petroliagis et al. (1996) were the first to study the November 1994 Piedmont case (hereinafter P94). They used the ECMWF global model operational at that time, both with the single deterministic forecast and with an ensemble approach. The spectral resolution of their deterministic run was T213 which roughly corresponds to about 60 km grid spacing at the Equator, while the resolution of the ensemble forecast was T63 (about 210 km). Despite the rough resolution of the model and the fact that the number of members (32 + the control member) of the ensemble was fewer than the one currently used, t
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