A study investigating impacts of sea level rise on coastal ecosystem services along the eThekwini Municipality coastline as a consequence of climate change and recommendations to build/enhance resilience.

Abstract

Climate change during the 21st century is caused by the rapid increase in global warming because of human activity. The consequences of climate change include melting glaciers, rising sea levels, and extreme weather. The primary cause of global sea level rise (SLR) is melting of ice on land, followed by ocean thermal expansion. Extreme events are happening more often and are becoming more intense due to greenhouse gas emissions from human activities. Coastal ecosystems are exposed to SLR and its physical impacts, such as flooding or salinisation, which in turn increase ecosystems’ vulnerability and decrease their ability to support livelihoods and provide ecosystem services such as coastal protection. Coastal ecosystems are also highly vulnerable to human-mediated drivers of climate change, such as land use change and coastal squeeze, because they are situated in the sea-land interface area that is favourable for urbanisation and development. This study focuses on the impacts of SLR on coastal dunes, and a protected tree species, Mimusops caffra, commonly known as coastal red milkwood, naturally occurring in part of the coastal forest in eThekwini Municipality. It further provides recommendations to enhance resilience along the Durban coastline. The results from the Coastal Vulnerability Index (CVI) analysis, classification of land use, developments impacted by a 300mm analysis, and the risk assessment of coastal ecosystems conclude that future SLR impacts will pose a threat to land demarcated under the Durban Metropolitan Open Space System, National Freshwater Ecosystem Priority Areas, and protected areas, as well as affluent high costing properties and coastal dunes and forests respectively, by a 300mm SLR along the eThekwini coastline in the next ±111 years if the current rate of SLR for Durban (2.74 mm/yr) remains constant. Further, whilst prior research suggests that the dieback of Mimusops caffra (M. caffra) is strongly related to fungal infections, results from this study indicate that M. caffra growing closest to the sea are stressed by environmental factors either wind or surge, thus increasing fungal infection as well. There is, however, little research on the impact of salt spray on these trees. Hence it is recommended that further investigation is required on milkwood to better understand the dieback observed in this study (i.e., due to fungus, or natural cause), especially as they are a protected species. Adaptation measures must be considered in areas identified as “high” risk for the protection of development from future SLR impacts, as well as maintaining natural areas where biophysical functionality is unhindered. From the CVI analysis, the regions which contain developments (i.e., private property) within the 100m HWM, both local government and homeowners should consider working together when installing geofabric sandbags to avoid increasing the effects of coastal erosion, as risks can be relocated elsewhere along the EM coast if individual action is not coordinated. From the classification of land use assessment, all areas within the respective land use that fall within the high-risk zone, the EM setback lines in conjunction with ecosystem-based adaptation should be implemented in order to protect these areas and ensure the functions of each land use is not unhindered. From the analysis of developments potentially impacted by future SLR, the total amount of estimated value of property loss within the given suburbs can assist coastal managers with deciding how money should be spent on defending properties and will yield the most protection from future SLR impacts along the EM coastline (i.e., a cost-analysis approach). Lastly, from the risk assessment of coastal ecosystems, future research on applying the vegetation index to certain parts of the EM coastline is necessary to get a better understanding of how vulnerable coastal ecosystems are to SLR impacts in Durban.