An innovative study by the University of Lisbon, Portugal, and USGS finds that historical photographs and postcards can provide rigorous scientific insight into how shorelines have changed over the past century.

Researchers from the University of Lisbon studying Conceição-Duquesa Beach in Cascais, Portugal, used ground-based, oblique images to quantitatively track shoreline evolution over 92 years, offering a novel method to understand long-term coastal change with ground-based imagery.

Turning Pictures into Coastal Data

While vertical aerial imagery has been a mainstay of coastal monitoring since the 1940s, and satellite data now revolutionize shoreline studies globally, data from earlier decades are scarce. That’s where ground-based historical images—such as vacation photos, news archives, and old postcards—come in.

In this study, scientists applied a novel image analysis method to postcard images of Conceição-Duquesa Beach from 1930 and 1960, as well as a contemporary smartphone photo from 2022. By registering and aligning the images to modern spatial coordinates, detecting shorelines within the photos, and correcting for perspective distortion and positional uncertainty, they were able to reconstruct past shoreline positions and measure their changes over time. 

A Rotating Shoreline

One consistent observation: between the early 20th and 21st centuries, the shoreline at Conceição-Duquesa Beach showed a significant counterclockwise rotation following the construction of the marina in 1998—a shift large enough to exceed any uncertainty in the analysis method. This long-term pattern underscores the significant impact of artificial coastal structures on shoreline dynamics, reinforcing the importance of integrating historical datasets and modern methodologies to assess and manage coastal changes effectively.

Broader Implications for Coastal Science

This study demonstrates how even older historical, corrected ground-oblique photographs can be used to quantitatively assess coastal change. The technique is adaptable, straightforward, and could be used for regions where other historical data sources are unavailable or incomplete.

Historical imagery held by libraries, museums, and other archives could potentially be of use with this methodology. With climate change and sea-level rise making coastal erosion and shoreline retreat more urgent global issues, having a longer historical record can significantly improve models of future change.

Read the study: Historical Coast Snaps: Using Centennial Imagery to Track Shoreline Change.