Flood in western Liguria on 26 October: our first analysis

During the night of 26-27 October in the area between Arenzano and Cairo Montenotte, in the province of Savona, heavy rainfall, widely forecast but difficult to localise due to the stormy nature of the phenomenon, unfortunately caused flooding and inundation with extensive damage that is still being estimated. On the one hand, very saturated soils due to the amount of rain that has fallen in the last two months, and on the other hand, the sea, which is much warmer than the seasonal average, are at the root of these extreme events, which are very localised and difficult to predict in their exact extent.

Arenzano and Cairo Montenotte, in the province of Savona, were among the areas most severely impacted by the intense rainfall of yesterday, which led to flooding and overflow on soils that were already saturated. [Fig. 1]

Pre-event soil moisture maps as of October 26 indicated high saturation levels across most of the territory, with a critical situation affecting almost the entire region. The saturation level, estimated at 23:00 on October 25 [Fig. 2], showed a saturation index exceeding 0.7 in the central-western areas of Liguria and above 0.9 in the Levante region. This indicator points to soil conditions that were already highly saturated, with very limited capacity for additional water absorption.

Over the past month, rainfall in these areas has totaled between 600 and 700 mm [data @ARPAL, Fig. 3], values equivalent to 50-60% of the average annual precipitation and surpassing the historical data usually recorded for the entire autumn season within just four weeks [Fig .4]. This critical condition made the area particularly vulnerable to the intense rainfall on October 26, significantly affecting Arenzano, Cogoleto, Varazze, and Savona.

What happened during and after the event? Continue reading the analysis on our website. ??