Can hot water discharged from industrial processes enhance the likelihood of waterspouts? Insights from high-resolution numerical simulations

Tornadoes and waterspouts are relatively frequent phenomena along the Italian coastlines,

particularly over the Tyrrhenian Sea, where specific meteorological and environmental conditions

foster their development. Despite their localized nature, tornadoes in Italy have caused significant

damage over the last decades, with casualties, injuries, and economic losses reaching 80 million

euros between 2007 and 2016. These numbers might still underestimate their actual impact, given

the lack of a comprehensive tornado database across Europe.

In this context, particular attention has been given to the role of environmental factors such as lowlevel

wind shear, convective available potential energy, and sea surface temperature (SST)

anomalies in modulating tornado occurrence and intensity. While many studies have analysed the

role of synoptic and mesoscale meteorological features in tornado formation over Italy, the

possible contribution of local SST anomalies, especially those induced by anthropogenic

processes, remains largely unexplored.

This study investigates whether the discharge of residual hot water from industrial processes into

the sea may locally enhance the likelihood of waterspout development. The analysis focuses on

Rosignano Solvay, a small town along the central Tyrrhenian coast, which experienced four

tornado or waterspout events in less than a decade — an exceptionally high frequency for such a

limited area. Using high-resolution numerical simulations (grid spacing up to 100 m) with the Meso-

NH model, we explore the sensitivity of convective development to SST modifications induced by

wastewater released into the sea near the Solvay industrial site. Simulations were performed

under both observed and perturbed SST conditions to quantify the potential role of localized

warming.

Results suggest that limited SST anomalies (ranging between 1 and 5 °C) over small areas

(approximately 15 km2) may induce modifications in the lower atmospheric thermodynamics,

favouring stronger updrafts in the presence of pre-existing favorable conditions, such as low-level

convergence. This highlights the potential contribution of anthropogenic processes to modulate

waterspouts, although their initiation is mainly driven by the local morphological setting.