Summary
The likelihood (i.e. probability) components of climate-related risks in Kiribati are evaluated for both present day and future conditions. Changes over time reflect the influence of global warming.
The risks evaluated are extreme rainfall events (both hourly and daily), drought, high sea levels, extreme winds and extreme high air and water temperatures.
Projections of future climate-related risk are based on the output of global climate models, for given emission scenarios. All the likelihood components of the climate-related risks show increases as a result of global warming, though for some the increases are small relative to the uncertainties.
Best estimates of long term, systematic changes in the average climate for Kiribati indicate that by 2050 sea level is likely to have increased by 37 cm, rainfall by over 20%, extreme wind gusts by 7% and maximum temperatures by almost 1.0 C.
The observed long term trend in relative sea level for Betio is 5 mm/yr, a rate far in excess of the observed local and global trends in mean sea level. For Betio an hourly sea level of 3.1 m above mean sea level is currently a 500-year event. It will likely be at least a ten-year event by 2025.
No significant long term trends are evident in the observed daily, monthly, annual or maximum daily rainfall. Currently a daily rainfall of at least 180 mm is a relatively rare event at Betio, with a return period of 16 yr. There is large uncertainty in the rainfall projections, with one model suggesting substantial increases in rainfall, two models suggesting only small increases, and one model indicating a small decrease in rainfall into the future. An extreme daily rainfall of 200 mm is currently a 30-year event. It will likely be a ten-year event by 2050. An extreme hourly rainfall of 80 mm is currently a 100-year event. It will likely become a 30- year event by around 2050.
A monthly rainfall below the ten percentile is used as an indicator of drought. Drought frequency is strongly linked to the occurrence of La Nina events. Six global climate models that were best out of 19 at simulating present day ENSO conditions show no significant changes toward El Nino-like conditions in the latter part of the current century. Therefore it is not yet possible to make consistent predictions about the future nature of La Nina and El Nino events and the implications for the frequency, duration and intensity of droughts in Kiribati.
Currently an extreme wind gust of 35 m sec-1 at Betio has a return period of 50 years. This will reduce to approximately 30 years by 2050.
There is relatively high confidence in projections of maximum air temperature. A maximum air temperature of 36 C is currently in excess of a 200-year event. By 2050 it will likely have a return period of 20 years. Open ocean water temperatures in excess of 32 C currently have a return period of 80 years.