Coupling land use evolution and subsidence in the Po Delta, Italy: Revising the past occurrence and prospecting the future management challenges.

The Po River delta is characterized by a large system of shallow lagoons, wetlands, and reclaimed lands. Like many other deltaic regions, the Po Delta has largely subsided due to natural processes and anthropogenic activities, with a strong impact on its geomorphological evolution and significant socio- economic consequences. This paper aimed at highlighting the evolution of the study area over the last 120 years, analysing the land-uses changes in relation to the land subsidence, and using these findings to discuss the main management issues of this fragile low lying area in the decades to come. The analysis of the land use evolution from 1892 to 2015 and the information derived from the metrics measurement suggest a simplification of the land use with a decrease of the saltmarsh extent and an enlargement of the agricultural cover. The analysis of land subsidence, mainly due to gas-bearing groundwater withdrawal, confirms a strong impact on the delta territory, and in particular on its geomorphological asset. In the early 1900s the elevation of the delta plain ranged between -1.0 and +1.6 m above msl, while in 2007 it reduced between -2.8 to +0.3 m above msl. The land reclamation projects have largely increased the farmland usable for crop production but the concurrent loss of land elevation has resulted in a territory extremely difficult to be managed. Because of its elevation, the delta is particularly vulnerable to weather and marine events. As a consequence, the present management of the area is mainly aimed at maintaining the agricultural productivity. Unfortunately, if the human impacts will continue with the actual trend, the stability of the natural ecosystems, such as the wetlands, which represent important socioeconomic realities, will be further undermined. Surely, the conservation of these natural environments should be a priority in the future land use management.