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.
During the event, soil saturation rapidly reached critical levels, exceeding 0.9 across almost all of Liguria [Fig. 5].
The 24-hour cumulative precipitation recorded at 00:00 on October 27 [Fig .1] highlights the intense events that affected the Savona coast and hinterland, confirming the significant impact of rain on an area already subjected to weeks of continuous accumulation.
The impact of this intense event is further evident in the 30-day cumulative precipitation updated at 00:00 on October 27, which includes the October 26 event that affected Liguria, especially in the areas of Arenzano, Cogoleto, Varazze, and Savona [Fig. 6].
Forecast models had anticipated a potentially intense event due to high sea temperatures (with anomalies up to 1°C) [Fig. 7] and atmospheric temperatures (anomalies up to 2°C near the surface) [Fig. 8], though accurately pinpointing the most intense phenomena in time and space proved challenging. These factors, along with atmospheric convergences over the Gulf of Liguria, amplified the intensity of the precipitation.
CIMA Research Foundation continues to closely monitor the situation over the coming hours and analyze the forecasts from our meteorological and hydrological models in support of the national Civil Protection system.