A Deluge in Italy

A Deluge in Italy
A Deluge in Italy

Parts of northern Italy have been impacted by severe flooding and landslides after heavy rainfall pummeled the Emilia-Romagna region on May 2–3, 2023. Rainfall amounts exceeded 20 centimeters (8 inches) in a 24-hour period in some locations. The floods disrupted rail services, forced hundreds of evacuations and rescues, and caused at least two deaths, according to news reports.

The image above (right), acquired by the Operational Land Imager (OLI) on the Landsat 8 satellite, shows flooding adjacent to the Lamone river on May 4, 2023. The image on the left, acquired by OLI-2 on Landsat 9, shows the same area on April 26, 2023, before the rains. These images are false-color, such that water appears dark blue, vegetation is green, and bare ground is brown.

As many as 13 rivers reached the highest alert level, with the Lamone river in the province of Ravenna seeing a particularly sharp rise. One sensor recorded its levels increasing from 1 meter (3.3 feet) to 11 meters (36 feet) in 24 hours, and one of its embankments near the town of Faenza failed.

Paolo Billi, a professor at the University of Ferrara, has studied Italian river hydrology and sediment transport. Acknowledging that these floods were destructive, Billi noted this type of event is not unusual in Emilia-Romagna or across the broader Italian landscape.

“The frequency of flash floods has increased throughout the last two decades,” Billi said, adding that the recent event fits the mold of such floods. These events are characterized by high-intensity rainfall over the course of several hours, sometimes affecting a very localized area. The 24-hour rainfall amount can equal 25 to 50 percent of annual precipitation, according to Billi. “In many cases, the negative effects of intense rainfall are exacerbated by urbanization and river channel narrowing that take land away from the river corridor,” he said.

The heavy rains also tend to cause rapid soil erosion and flush large amounts of sediment out to sea. The OLI on Landsat 8 captured this image (above) of sediment-laden waters flowing from multiple rivers into the Adriatic Sea on May 4, 2023.

The Emilia-Romagna region has been undergoing severe drought. Last summer brought low rainfall, higher-than-average temperatures, and critical water shortages. The level of the nearby Po River, which dropped to concerning levels in the summer of 2022, swelled by 1.5 meters (5 feet) in this rain event. However, for the second year in a row, the amount of water available from snowpack in the Po basin is well below average.

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Lindsey Doermann.

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