Vulnerability assessment of mangroves to climate change and sea-level rise impacts

Joanna C Ellison

doi:10.1007/s11273-014-9397-8

Abstract

Climate change, particularly its associated sea level rise, is major threat to mangrove coastal areas, and it is essential to develop ways to reduce vulnerability through strategic management planning. Vulnerability has three dimensions of exposure to stresses, associated sensitivity, and related adaptive capacity, and ways to measure components of each were trialled at sites in Africa and the South Pacific to develop an analysis procedure based on ranking. The approaches of the ranking system for vulnerability assessment of mangrove systems integrate biotic and abiotic factors along with human management components, using validated methods previously developed for other research questions. These include determining mangrove forest health, adjacent ecosystem resilience, the extent and effects of human impacts, and the environmental conditions of different mangrove settings. Results of the vulnerability assessment ranking using up to 20 measurements found all sites to have some components of vulnerability. Douala Estuary, Cameroon showed the highest vulnerability, owing to low tidal range, impacts from non-climate stressors, and evidence of moderate seaward edge retreat. Tikina Wai, Fiji showed inherent vulnerability owing to location on a subsiding coastline with a low tidal range, but this was offset by strong local community management capacity. Rufiji Delta, Tanzania showed inherent resilience owing to location on an uplifting coastline with a macrotidal range, but showed vulnerability from human impacts and lower local community management capacity. The most critical components to the vulnerability assessment were found to be exposure components of relative sea level trends and sediment supply, and sensitivity components of forest health, recent spatial changes and net accretion rates. The results provide a baseline against which to establish long-term ongoing monitoring, allowing continued assessment of the complex dynamics of climate change impacts, and providing an information base for strategic management decisions.

Highlights

Despite the mangrove values of coastal protection, fish and wildlife habitats, sediment and pollution filtering and carbon sequestration (Mumby et al 2004; Spalding et al 2010; Bouillon 2011) mangrove areas have rapidly reduced in recent decades (Giri et al 2011a) and many remaining habitats suffer from unsustainable use (Spalding et al 2010)
With coastal risk classifications placing mangroves among the highest ranked of shoreline types in their vulnerability, this study develops a higher resolution of ranking within such mangrove shorelines, using the most relevant of risk variables combined with measurements of components of mangrove exposure, sensitivity and adaptive capacity
The vulnerability trials conducted in this study found that the criteria that should guide a vulnerability assessment described by Schroter et al (2005) were applicable to mangrove areas

Summary

Introduction

Despite the mangrove values of coastal protection, fish and wildlife habitats, sediment and pollution filtering and carbon sequestration (Mumby et al 2004; Spalding et al 2010; Bouillon 2011) mangrove areas have rapidly reduced in recent decades (Giri et al 2011a) and many remaining habitats suffer from unsustainable use (Spalding et al 2010). Degradation and loss of these coastal buffering systems due to climate change and direct human impacts negates the coastal protection they provide during extreme events and increases their vulnerability, with significant environmental, economic and social consequences for coastal people. Wetlands Ecol Manage (2015) 23:115–137 interpretation of vulnerability (Remling and Persson 2014), where the solutions are in reducing exposure through climate change mitigation, and technical and sectoral adaptation to limit negative outcomes. Vulnerability assessment incorporates a significant range of parameters in building quantitative and qualitative understanding of the processes and outcomes of vulnerability (Adger 2006), and its application to intertidal mangrove ecosystems has the capacity to improve climate change adaptation planning

Methods

Results

Discussion

Conclusion