Coastal flooding in the Maldives: an assessment of historic events and their implications

With many inhabited islands only at about 1 m above mean sea level, the Maldives is among the nations most threatened by coastal flooding and sea level rise. However, the understanding of recent coastal flood events in the Maldives is limited and is important to understanding future flood threats. This paper assesses (1) the sea level and wave climate of the Maldives, (2) the sea level and wave conditions during recent coastal flood events, and (3) the implications for flood management and future research. The analysis uses observed still water levels (1987-2015) and hindcast wave conditions (1979-2015). Two significant flood events on 10-13 April 1987 and 15-17 May 2007 are examined in detail. This shows that coastal flooding in the Maldives occurs due to multiple interacting sources. These include long-period (up to 20 s) energetic waves generated in the Southern Ocean combined with spring tides. Wave run-up (mainly wave set-up) appears an essential mechanism for a flood, but is currently poorly quantified. However, as sea levels continue to rise the conditions that produce a flood will occur more frequently, suggesting that flooding will become common in the Maldives. This analysis is a starting point for future research and highlights the need to continue research on flood sources, pathways and receptors, and plan adaptation measures. Priorities include monitoring of waves, sea levels and flood events, and a better understanding of set-up (and other shallow water processes over reefs).