Multi-temporal analysis of remote sensing and in situ data for the study of delta systems

Understanding the future evolution of the Po delta is fundamental to planning and management of this heavily-populated low-lying delta areas. Through the Holocene it was shaped by the interacting effects of sediment supply, sea level and marine reworking. Unlike traditional models, tectonics and climate have also played important roles in the delta’s evolution. Superimposed upon the active, but relatively unknown, natural system, human alterations to natural processes have become increasingly important, both (1) indirectly by changing land use and water management within the catchment, and (2) directly within the delta itself due to groundwater withdrawal, flood mitigation efforts, infrastructure development, etc. This human influence has intensified in the near present times as coastal and catchment populations grow, urbanise and develop their economies.

The work presented in this paper aimed at investigating the temporal evolution of patterns and processes on the Po Delta (Italy), using remotely sensed datasets. An innovative integration of remote sensing and monitoring method (Permanent Scatter Interferometric Synthetic Aperture Radar - PSInSAR, Small BAeline Subset - SBAS and Empirical Orthogonal Function – EOF analysis of 20 years of Landsat) has been used to study the temporal evolution of subsidence and its correlation with natural and anthropogenic causes. Results show an increase of the subsidence rates obtained for the last decade: the amount of subsidence due only to natural causes is typically a few millimeters per year, while the man-induced subsidence reaches values of several millimeters per years. Marshlands reclamation, groundwater pumping for agricultural and industrial purposes and methane extraction from gas fields near the coastline are the principal anthropogenic causes. Hence the final study results would emphasise the multiple factors and stresses that are influencing the delta evolution. Such a framework also allows the full range of management responses to be considered. In addition to traditional engineering approaches in deltas, there are opportunities to work with nature. The deltaic system has the capacity to be highly resilient in the face of these multiple pressures with important ecological and social benefits.