Adaptation to flood risk on Reunion Island (France): A historical perspective from photographic evidence

Reunion Island, situated in the Indian Ocean, has faced significant flood risks since its early settlement in the 17th century. Currently, the island comprises six territories identified as flood-risk areas (TRI). Understanding the historical context of this risk is crucial for effective management and adaptation strategies. To explore the evolution of flood risk, we examined a collection of historical postcards from the late 19th to early 20th centuries, archived at the Archives Départementales in Saint-Denis. We selected approximately fifty postcards based on specific criteria: the relationship between habitats and rivers, the need for a comprehensive spatial perspective, and the representation of diverse watersheds across the island. Field missions conducted in 2024 and 2025 allowed us to replicate the photographs at the same locations as depicted on the ancient postcards, facilitating a direct comparison of changes in land use and hydromorphological structures (including “planèzes”, slopes, and valley floors). Our findings reveal significant insights comparing land use from the late 19th century to the present day (2024-2025). We observed new housing developments on planèzes, which have heightened risks of urban runoff and flooding associated with small rivers. Certain regions remain unchanged, indicating that the original placement of habitats was appropriate, situated on alluvial terraces and slopes protected from landslides and debris flows. In contrast, urban encroachment into the active channels of large rivers (“ravines”) has created substantial risks for local populations. These findings align with the analyses of D. Lorion (2013), who characterizes the rise in flood-risk areas during the 1970s and 1980s as a manifestation of the 'security utopia' created by river embankment systems.

 

References

 

Lorion D. (2013) – From a utopia of security to the integrated management of drainage basins: The example of Reunion Island (France). In Arnaud-Fassetta G., Masson E., Reynard E. (Eds.) European continental hydrosystems under changing water policy. Friedrich Pfeil Verlag, München, 87-98.