A sinking landscape
The Po Delta, the largest wetland in Italy, is a changing environment, not in a good way. It is sinking. This phenomenon, called subsidence, results from a combination of natural and human-driven processes. The delta itself is geologically young, formed from vast quantities of sediment deposited by the Po River over thousands of years. These soft, Holocene-era deposits naturally compact and settle over time, causing the ground level to slowly decrease by a few millimeters per year.
The natural rate of sinking was dramatically accelerated in the mid-20th century. After World War II, intensive extraction of methane-rich groundwater from onshore and offshore reservoirs began. This large-scale removal of subsurface fluids drastically reduced the pressure within the sedimentary layers, causing the ground above to collapse downwards. Between 1951 and 1957, subsidence rates peaked at an astonishing 250 to 300 millimeters per year. In response to the rapid sinking, the Italian government halted major methane-water extraction in the early 1960s. This action successfully reduced the most extreme rates, but the delta continues to sink at an alarming pace, now primarily driven by the ongoing compaction of its young sediments and more localized water extraction.
Measuring the drop from space
Monitoring a landscape that is slowly and unevenly disappearing requires advanced technology. Scientists use a combination of ground-based Global Navigation Satellite System (GNSS) stations and a satellite-based technique called Interferometric Synthetic Aperture Radar (InSAR). InSAR satellites, like Europe's Sentinel-1, bounce radar signals off the Earth's surface and measure the return signal's phase. By comparing images taken at different times, they can detect millimeter-scale changes in ground elevation across vast areas.
These precise measurements reveal a complex picture. The easternmost parts of the delta, near the river mouths, are sinking the fastest, with current rates up to 10-15 millimeters per year. This is significantly faster than the global average sea-level rise of about 4 millimeters per year. The cumulative effect is dramatic. Some areas of the delta have dropped by as much as 4 meters since the 1950s. A large portion of the region now lies below mean sea level, protected only by an extensive and vulnerable system of levees. The consequences are severe, including the permanent submergence of coastal land, increased flooding risk during storm surges, and saltwater intrusion into freshwater aquifers used for agriculture. Entire islands, like the former rice farm at Isola Bonelli Levante, which was abandoned in the 1990s, have been lost to the Adriatic Sea.