Climate information for risk management
The Intergovernmental Panel for Climate Change (IPCC) Fourth Assessment Report (AR4) released in 2007 identified that while Pacific Island states are likely to be some of the most seriously impacted, the volume of scientific research relating to climate and small islands within the region has decreased notably since publication of the IPCC Third Assessment Report (TAR) in 2001, compared to the period between the second assessment report in 1995 and 2001. Indeed little specific work has been carried out to quantify the potential changes on hazard occurrence and magnitude due to climate-related hazard events under potential future emission scenarios and the implications this has on the specific risks facing different Pacific Island communities (i.e., risks at the island, community and village levels), different economic sectors, or to essential infrastructure. A key objective of the Climate information for risk management component of the Kiribati Adaptation program was to derive such I-Kiribati-specific climate change projections to be used to underpin and guide risk assessment and adaptation planning. This involved deriving information on:
- extreme rainfall,
- drought,
- sea-level and wave conditions, as well as site specific shoreline wave conditions, wave run-up levels and overtopping amounts along the different shorelines of Tarawa,
- and how these may change under different climate change scenarios
Projection timeframes for climate-change scenarios were chosen that provided the most meaning in Kiribati. Two criteria were used to choose the timeframes:
- Terms of government: Under the Kiribati constitution, terms of government are four years. A president is only allowed to serve three consecutive terms – or 12 years. Hence, a scenario period of 24 years would mean that at least two presidents have served.
- Generations. This criteria was summarised as: “the first scenario should be when we are all old men and women and our children have children”. Subsequent scenario periods should take the perspective of each subsequent generation.
Based on 12 Global Climate Models for the Kiribati region, by the period 2060-2084 (Great-great grandchildren or Tibu mwamwanu), average temperatures are likely to rise (relative to the average temperatures between 1980-1999) by between 0.4 to 4.7ºC. Kiribati selected 3 emission scenarios to carry out climate change assessment and sensitivity analysis – B2 (lower bound of climate model output), A2 (average range of model output), and A1FI (high range of model output). All Global Climate Models suggest that along the equator in the Pacific that average rainfall amounts will increase under a warmer climate. However, rainfall in Kiribati will still continue to vary from year to year, depending on changes in El Niño-Southern Oscillation, for which there is not yet any model consensus As well as changes in average rainfall amount, under a warmer climate the intensity of extreme rainfall events will increase. The magnitude of change in rainfall intensity will depend on how much temperature rise occurs and on the particular severity and duration of the extreme rainfall. As an example a rainfall amount over one hour that presently has a 1% chance of occurring in any one year would be experienced from anywhere between twice to almost seven times as frequently, depending on the emission scenario, by the period 2060-2084. Drought conditions on Kiribati are highly dependant on natural climate fluctuations, particularly the El Niño Southern Oscillation. There is less understanding of how drought may change in the future, due to our lack of understanding of how El Niño-Southern Oscillation characteristics will change in the future, but it is likely that:
- Drought characteristics will generally stay much the same over the next 100 years.
- There will be some periods when drought may be slightly more prevalent during this time. In Western Kiribati this will still be strongly lined to periods of La Niña.
Global sea-level have risen by between 1.2 to 2.2 mm per year over the 20th century. On Kiribati sea-level have been measured on Tarawa only since 1974. Over this period, to the end of 2008, average sea-level rise has been at a rate of about 1.8 mm per year. Since 1993 the rate has been 3.5 mm per year but at lease some of this increase in rate is likely to be due to natural climate variability influences rather than wholly due to any long-term increase in the rate of sea-level rise. Extreme wave and water level information was derived for both Tarawa lagoon and ocean shorelines using a combination of the sea-level data from the tide gauges at Betio and wave and hydrodynamic modelling for both the present day and future climate change scenarios. Whilst Kiribati does not experience any significant storm surge due to it being close to the equator and is outside the zone of direct tropical cyclone occurrence, storm events coinciding with high tides can inundate significant areas of land. As part of the project a detailed assessment of the joint occurrence of extreme waves and water levels, the impact of climate change on these processes, and what this means for wave conditions reaching the shoreline, wave run-up and overtopping was undertaken. The wave and water level data was incorporated in to a database and calculator that enables the impact of different emission scenarios on tide and extreme water levels, wave-run-up levels and wave overtopping to be calculated for user-selected locations on Tarawa. Increases in sea level will enable higher wave conditions to translate over the reef or sand flats that surround the shoreline on Tarawa. As both wave run-up and overtopping of coastal defences can be extremely sensitive to small changes in water levels and wave conditions even very small changes in sea-level rise may have a significant impact on inundation of the immediate coastal margins of Tarawa, and essential infrastructure, such as the causeways between the various islets. As an example for a storm condition that has a 10% chance of occurring in any one year and for the low, medium and high I-Kiribati scenarios, wave overtopping of the causeway between Bairiki and Betio could increase by 59%, 141% and 275% respectively by the period 2060 to 2084.
This information was prepared by our partners at the New Zealand National Institute of Water and Atmospheric Research. Read more about their work assisting us in dealing with climate change on the NIWA website.
