A framework for assessing the space needed for dune-based coastal adaption at multiple time scales.

Under current conditions, the Spanish Mediterranean coast is already presenting hotspots of extreme exposure to coastal hazards and recurrent damage, making it necessary to adopt disruptive adaptation strategies as opposed to the classic expectation of full protection. This situation is expected to worsen under the effect of sea level rise, which will increase existing erosion rates, with some areas being fully eroded due to the lack of accommodation space to allow natural adaptation to the new conditions.

In this context, nature-based solutions (NBS) are becoming one of the main type of measures to be favored in order to be more climate-resilient and thus support EU policy priorities. Although research on the effectiveness of most nature-based coastal protection methods is still limited, some of them such as dune systems and sand banks have been classified as essential for future coastal defense.

In highly-developed coastal zones, which are the most at risk, the lack of the sufficient space limits the viability of using NBS as they cannot be accommodated. Thus, the existence of accommodation space is the required condition to permit the beach migration and rebuilding under SLR, otherwise will progressively decline and ultimately disappear. It has to be stressed that the accommodation space is a relative concept, being related to the expected magnitude of the shoreline retreat at a given time horizon under a given climate forcing scenario. 

Within this context, this work presents a regional-scale framework to assess the accommodation space needed to adopt dune-based NBS planning as a coastal adaptation strategy, by integrating predictions of accommodation space needed to cope with coastal hazards under current and IPCC AR6 climate scenarios and for different time horizons relevant for planning purposes (up to 2100), and to enable dune development. The hazards considered are (i) long-term (decadal scale) coastline evolution; (ii) storm-induced erosion; (iii) SLR-induced erosion; (iv) permanent inundation due to SLR; and (v) storm-induced flooding. The framework applies to the Catalan coast, a 600 km long stretch of the Spanish Mediterranean coastline.

This work was supported by the Spanish Agency of Research in the framework of the CoastSpace project, TED2021-130001B-C21 (MCIN/AEI/10.13039/501100011033).