Roger McLean School of Physical, Environmental and Mathematical Sciences

University of New South Wales at the Australian Defence Force Academy

Canberra, ACT 2610, Australia

Towards a coastal vulnerability

typology for small islands:

assessing island diversity (and

similarity) via a common framework

Wed 8 July Landscapes of Our Common Future:

Session 2210:Coastal Impacts of Climate Change

Our Common Future under Climate Change

1. Need to acknowledge the heterogeneity and

complexity of small island states and territories

2. Need to better understand within

country/territory differences in vulnerability

3. Need to include a range of climate-change

related projections and not just temperature and

sea level

IPCC AR5 WGII – Chapter 29 Small islands

One of the key messages Small islands do not have uniform climate

change risk profiles.

Research and needs challenges:

Australian Government

responded through the

Pacific-Australia Climate

Change Science and

Adaptation Programme

(PACCSAP) funded by AusAID

administered by Department

of the Environment).

Commissioned regional study

of coastal susceptibility

based on geomorphic

characteristics of Pacific

Islands and climate–ocean

drivers.

Aims of project:

1. Identify typical island types for 15 partner

countries in Pacific – data base of 1532 islands

2. Develop a regional-scale ‘indicative susceptibiity’

of island coasts using simple criteria

3. Identify key climate-ocean processes now and in

the future that can result in coastal change

4. Develop a regional-scale ‘coastal sensitivity’

based on geomorphic characteristics and

relevant climate-ocean processes

5. And ultimately develop a regional coastal

vulnerabiiity assessment

1. Island Types

Based on two criteria:

Lithology (rock type)- 5 types • volcanic

• limestone

• composite

• unconsolidated sediment (reef)

• continental

Elevation • high > 30 m above sea level

• low < 30 m above sea level

8 Island types

1/2. Volcanic High and Low Islands: Islands composed of at least 80% igneous rock with 30m above MSL to separate high and low islands

3/4. Limestone High and Low Islands: Islands composed of at least 80% calcareous rock with 30m above MSL to separate high and low islands.

Bellona, Solomon

Islands

Luon. Solomon

Islands

Tomowas, Federated

States of Micronesia

Lifuka, Tonga

Aniwa, Vanuatu

5/6. Composite High and Low Islands: Islands composed of both volcanic and limestone rock types with each type being <80%, with 30m above MSL to separate high and low islands

7. Reef Islands: Islands composed of at least 80% unconsolidated sediments and < 10m high.

Aitutaki, Cook

Islands

Onotoa, Kiribati

Vaitupu, Tuvalu

8. Continental Islands: Islands composed of at least 80% continental rocks e.g granite (Grande Terre, New Caledonia)

Island Types

Island types

by area

Island types

by number

Island types

in 15 Pacific

Island

Countries

by number

Island types in

15 Pacifc

Island

Countries by

area

2. ‘Indicative Susceptibility’ of Island Types

Certain island types are inherently more susceptible (less

resistant) to physical change than others.

Four variables:

• lithology/rock-type (for erodability-hard rock to soft

sediment; drainage-surface/subsurface)

• maximum elevation (higher less susceptible)

• island area (larger less susceptible)

• island shape (circularity) (angular more susceptible has

longer shoreline)

were used to develop a measure of indicative susceptibility.

A five-point scale susceptibility rating was derived for all

1,532 islands and for the island types within each country.

‘Indicative’ Susceptibility

Luon V 2 0.9 1 49 m 2 5 km2 4 Total 9 Low

Bellona L 4 0.7 2 79 m 2 23 km2 3 Total 11 Mod

Onotoa R 5 0.2 4 2 m 5 4 km2 4 Total 18 V

High

Island ‘Indicative Susceptibility’

Downscaling Indicative Susceptibility: 6 criteria

Adding more

criteria (11) Backshore: height

,sediment

Intertidal: platform

mangrove

Reef: fringing, barrier

Subtidal: slope

Coastal Sectors

Luon Island

• volcanic

• sheltered

• fringing reefs

• rocky bluffs

• 3 coast types

• 6 sectors

• all moderate

susceptibiity

Aitutaki

• composite

• 2 contrasting

island types

• 11 coastal

sectors

Susceptibility

1.1 High

1.2 & 3 Mod

2.1-2.5 Low

3. Climate-ocean processes that result

in coastal coastal change:

present and future

• Tidal type and range

• Ocean waves and swell

• Tropical cyclones

• Sea level and ENSO

Diurnal: Lonbrum PNG

Tidal type

Semi-diurnal Betio Kiribati

Tidal Range (m)

Pacific Wave Climate

1.Trade wind waves

2.Westerly storm waves

3.Distant- source swell

4. Tropical storm waves

Sea Level

Change

1993-2009

Average sea

level with

ENSO phase

El Nino

La Nina

Sea Level • Global sea level will continue to rise and likely accelerate.

• Projections for 2081-2100 (relative to 1986-2005) range from

0.26-0.55 m (RCP 2.6) to 0.45-0.82 m (RCP 8.5).

• Strong regional deviations from global projections of 10-20

% can be expected in tropical Pacific.

• ENSO will remain dominant driver inter-annual variability

Tides • Tide character unlikely to change except in enclosed seas

• Effect of sea-level rise felt most in areas of low tidal range –

base of mean tidal envelope could be raised

above present MSL or even high water.

Projected changes to climate-ocean

processes to 2100

Waves • Decrease in Hs of c.7% (0.1m) along the equator .

• Pole-ward shift in extra-tropical cyclone belts-reduce

damaging distant-source swells.

• Increase in trade winds in SH subtropics.

• Decrease in Hs over most oceans but increase in

Southern Ocean affects south coasts of islands.

Tropical cyclones and storms • Global frequency expected to decrease or remain

unchanged.

• Global increase in TC intensity/maximum wind speed.

• Equator-ward movement of TC tracks in NH;

pole-ward in SH.

Incorporates 2 main factors into measure:

1.Indicative susceptibility of islands/coasts

2.Key projected coastal processes in Pacific

Water level: Tide range + ENSO range

Waves: Wave height (Hs) + TC

Sea-level: Sea-level change + max tide

4. Coastal (Geomorphic) Sensitivity

to Change

Composite Water Level

Tide range + ENSO range

TC frequency + Wave height

Projected sea level

2055 with high tide (m)

Coastal (geomorphic) sensitivity

Summary: Developed a consistent and

defensible framework towards a regional

vulnerability assessment. But it falls short.

Need:

1.To develop a coastal typology

(like the island types) that is

appropriate

across the region (25 to 30 coast types)

2. To add human factors- settlement,

land use, population, infrastructure

etc

3. Upscale from coastal segment to whole

island to all islands

Thank You

Thanks to colleagues Patrick Nunn, Laiit Kumar, Ian Eliot.

And to Neil Lazarow, Kiri Yapp, Sam Hussey-Smith, Dominic

Ransan-Cooper, Lalarge Cherry of the Australian Govt

Department of Climate Change and Dept of the Environment