Intense rains that triggered floods in Italy may become more common

The intense rains that triggered flash flooding and mudslides in northern Italy during October 2011 were unusual but not completely unexpected according to research performed by scientists at the Institute of Atmospheric Sciences and Climate in Bologna, Italy.

The floods in Italy destroyed many buildings and took the lives of at least nine people. Coastal areas near Liguria and Tuscany were particularly hit hard by the heavy rains and Italy has declared a state of emergency for regions damaged by flood waters. On November 3, 2011 emergency management officials evacuated the town of Vernazza in anticipation of more heavy rains to come.

Dave Petley is a professor in the Department of Geography at Durham University in the United Kingdom and author of The Landslide Blog. In a recent post, he noted that rains in northern Italy reached an intensity of over 140 millimeters per hour (6 inches per hour) on October 25, 2011. Rainfall intensities greater than 140 millimeters per hour are unusual and rarely seen outside of hurricane and tropical cyclone conditions.

A research team led by Michele Brunetti at the Institute of Atmospheric Sciences and Climate in Bologna, Italy analyzed trends in rainfall across Italy in a 2004 paper published in the Journal of Geophysical Research. The scientists observed that from 1880 to 2002 Italy has become somewhat drier as indicated by a decline in the number of wet days that occur annually. However, precipitation intensity has increased over the past 120 years in Italy’s northern regions. These data suggest that northern Italy may be in for more frequent extreme weather events in the future.

Italy has some of the longest-running meteorological records in the world. Many cities in Italy such as Bologna, Milan and Rome began collecting meteorological data back in the 1700s. Long-term meteorological datasets are valuable tools that help us to understand our changing climate.

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