Using remote sensing to assess the role of coastal ecosystems in the protection against erosion in the Caribbean
Résumé
Most of the world's coastal environments are experiencing the negative effects of
climate change combined with anthropogenic activities. In order to limit those effects,
policy makers and managers need to understand the process that is taking place on
the coast. Where the safety of goods and persons, but also the tourism economy
linked to the preservation of beaches and the natural heritage of these interface
environments, rich in biodiversity (mangroves, coral reefs, seagrass beds) are the
primary concerns. CARIB-COAST is an international project led by the BRGM
(https://www.carib-coast.com/en/). Its ambition is to pool, co-construct and
disseminate approaches to monitoring, coastal risk prevention and adaptation to
climate change in the Caribbean. An analysis of existing monitoring practices
allowed to better constrain the needs for coastal monitoring in the Caribbean
territories and propose a strategy based on the experiences carried out in the
different participating countries. In this respect, pilot sites have been identified in
Guadeloupe, Martinique, Saint-Martin, Jamaïca, Puerto Rico and Trinidad and
Tobago to strengthen or initiate coastal monitoring approaches and assess the role
of coastal ecosystems like mangroves, seagrass and coral reefs in the protection
against coastal erosion. Many studies focus on Coastal vulnerability Index (CVI), one
of the predictive approaches to coastal classification by incorporating various coastal
variables. This index-based method simplifies a number of complex and interacting
parameters, and is widely used to measure vulnerability of the coastlines. Given the
extent of the area of interest, the diversity of pilot sites and variables to be integrated
in the CVI calculation, and the intent to develop a common approach for all areas,
this study has taken advantage of current available remote sensing data to construct
a vulnerability index.In this study, the proposed Ecosystem-based Coastal
Vulnerability Index (EBCVI) involves a wide range of variables, mainly focused on
ecosystem characteristics, represented by diverse data types, and their contribution
to coastal protection against erosion. In particular, we used remotely-sensed data to
contribute to (i) current mangrove restoration actions, (ii) the evaluation of coral reefs
evolution and their role on erosion and (iii) the promotion of seagrass protection.
The calculation of the EBCVI relies on:
● the production of mangroves distribution maps, using high resolution
Sentinel 2 data in a supervised classification approach.
● the use of seagrass and coral reefs distribution and types maps
provided by the Allen Coral Atlas
● the calculation of surface metrics (texture, density, fragmentation…), from
very high resolution Pleiades and Planetscope images, describing
ecosystems at a fine scale.
● the application of a multi-criteria analysis to these metrics combined with
other variables (geomorphology, socio-economics...) in order to map
coastal vulnerability by assessing EBCVI values for each pilot site. The
knowledge of local partners will allow a weighting of the importance of
each criteria in the index.
This index has the potential to be used as a management tool in order to assess
impacts of climate change on Caribbean coasts through the development of existing
observatories and good practices around a common protocol, and triggering (iv) new
initiatives in the Caribbean region, enabling an appropriate implementation of short
and long term policies dedicated to coastline protection.