Helmholtz-Zentrum Geesthacht, 2017-09-23
http://www.hzg.de/030646/index_0030646.html.en

Impact, vulnerability and adaptation in most vulnerable regions: Small Islands (the Maldives)

This WP focuses on climate change impact, vulnerability and adaptation due to a global averaged surface temperature change of 2°C from pre- industrial level for the Coastal regions of Small Islands.

© Ahmed Shan, EPA, Maldives © Ahmed Shan, EPA, Maldives

Small, low-lying islands have been seen as highly vulnerable to sea-level rise since the issue of climate-induced sea-level rise was raised in the 1980s. Regional assessments have highlighted potential impacts - in the worst case leading to forced migration - and subsequently high damage costs. Urbanisation and especially migration to the capital city is widespread: presently around a third of the national population live in the capital -- Malé, making it one of the most densely populated cities in the world with 50,000 people/km2. But, with rising sea levels how will the Maldives cope?

Hulhumale being developed to release the population pressure in the capital city of Male’. (From http://www.travelalltogether.com) Hulhumale being developed to release the population pressure in the capital city of Male’. (From http://www.travelalltogether.com)

The Maldives comprises 1,192 low-lying coral atoll islands, located in the Indian Ocean, with elevations typically within 1-m of current high tides. 200 of the islands are inhabited. The islands are economically dependent on international tourism and fisheries. The Maldivian Ministry of Environment and Energy, together with the University of Southampton, UK and Global Climate Forum, Germany are assessing the impacts of sea-level rise, focusing on a relatively new artificial island, Hulhumalé.

Hulhumalé is a 200 hectare island claimed from a reef area during the late 1990s to relieve population pressure on the nearby capital city of Malé. Hulhumalé has experienced rapid and large population growth, reflecting the high demand for land and housing in this part of the Maldives. The island was built approximately 2m above mean high water, and has so far been safe from inundation.

Hulhumalé is an entirely artificial island claimed over the reef flat and includes the main airport @ HDC Hulhumalé is an entirely artificial island claimed over the reef flat and includes the main airport @ HDC

Our study considers if and when the island may experience inundation due to extreme sea-level events and/or wave overtopping, and when this may occur with rising sea levels. We are:

(1a) Collating land datasets to define land elevations and associated assets.
(1b) Collating oceanic datasets to determine the frequency of extreme events (sea levels and waves), and selecting appropriate sea-level scenarios.
(2) Using an overtopping model (SWAB) developed by the University of Manchester, UK to determine volume of overtopping for plausible present and future events.
(3) Investigating what parts of the island could be inundated using LISFLOOD.
(4) Determining what infrastructure and assets on the island are at risk.

Overtopping Model (SWAB)

Initial results indicate that relative sea-level rise from the tide gauge (extracted from PSMSL, 2014) nearby Malé is approximately 4mm/yr since 1990 – faster than the global average, although longer records are preferred. Globally, sea-level rise is expected to accelerate, with up to approximately 1m of rise by 2100 (taking a high-end scenario from Church et al. 2013). This trend would be expected in the Maldives.

Mean Sea Level Malé, Hulule

Relative sea-level rise in Malé. Data extracted from PSMSL (2014). Click picture to enlarge Relative sea-level rise in Malé. Data extracted from PSMSL (2014). Click picture to enlarge

Two particular events which caused flooding in 1987 and 2007 were due to long period energetic swell waves, the latter generated off the coast of South Africa. In the 2007 event, Malé was flooded, but Hulhumalé was flood free. Using this event as an example of an extreme event, we are assessing how overtopping could change with sea-level rise. Initial results suggest that under swell/surge conditions, it could take tens of centimetres of sea-level rise before overtopping occurs.

Example of significant wave heights in the Indian Ocean, May 2007 (data extracted from WaveWatchIII) Example of significant wave heights in the Indian Ocean, May 2007 (data extracted from WaveWatchIII)

In our future work, we will better quantify our initial results, and also consider the role of adaptation. Adaptation, such as building sea walls or replenishing beaches could help to reduce impacts. As sea-level rise has significant inertia and will continue even if temperature rise stabilises (the so-called commitment to sea-level rise), we will consider changes beyond 2100 if possible.

NOAA Wave Watch III

Participants

SOTON (lead)
HZG, MHE, GCF

Deliverables