Storm surges occur when high winds and low atmospheric pressure raise water levels at the coast, causing sea water to surge onto the land. They are a major threat to low-lying coastal areas and their inhabitants. The largest storm surges, caused by tropical cyclones, may result in peak water levels exceeding 7 m in height, causing extensive flooding, loss of life and damage to property. Global climate change may result in increased storm surge flooding in some areas, through intensification of the cyclones driving the storm surges and as a result of sea level rise. Mangroves can reduce storm surge water levels by slowing the flow of water and reducing surface waves. They could potentially play a role in coastal defence and disaster risk reduction. This report reviews available information about the capacity of mangroves to reduce storm surges, in order to inform decision makers, planners and coastal engineers about the potential role that mangroves can play in coastal defence against storm surges.
The first section provides some basic information about storm surges and the factors affecting surge levels and surge reduction. Section 2 explores the evidence for mangroves reducing storm surge water levels, followed by Section 3, which focuses on the attributes of mangroves that affect the level of storm surge reduction. Section 4 reviews the effect of mangroves on surface wind speeds, which affect wave generation and hence surge water levels. Section 5 reviews the literature on the ability of mangroves to reduce loss and damage caused by storm surges. Section 6 then explores how mangroves are themselves affected by storm surges and cyclones.
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