Australian Actuaries Climate Index component graphs and data

There are six individual indices available which have been chosen for the impact and risk they pose to people and the economy. The indices are described in the table below.

Temperature



For the high temperature, the AACI measures the change in the proportion of days in a month on which the maximum and minimum temperatures exceed the 99th percentile of the reference period distribution for the relevant day. The results for the maximum and minimum temperatures are then averaged. The low temperature measure is calculated using a similar process by looking at the frequency above the 1st percentile. Both the high and low temperature components therefore record if there is a warming in temperature.

Precipitation



Extreme precipitation over short periods is a key driver of flood and storm damage. The rainfall component of the index focuses on extreme rainfall over a consecutive 5-day window.

Wind



During severe wind weather events such as storms and cyclones, it is the maximum wind gusts that are likely to lead to higher risk and damage. The wind metric measures the monthly frequency of daily maximum wind gust above the 99th percentile.

Consecutive dry days



Consecutive dry days is included in the Index as an indication of drought conditions. It is defined as the number of consecutive days with less than 1mm of rain up to a maximum of 365 days. The cap is included for practical purposes and has no material impact on the Index.



Sea level



The sea level measure tracks movements in the monthly maximum observed sea level, an important risk factor for coastal inundation. This measure uses sea level movements relative to land. Using this measure doesn’t allow for land movements which can be caused by a mixture of climate and non-climate (tectonic movements) related factors, but this is the most readily available measure and is measured accurately by tide gauges.

Further information on component definitions is available in the  Design Documentation .

• The  Actuaries Climate Index ™ (ACI) has been developed in North America with a similar objective.
• CSIRO and Bureau of Meteorology, Climate Change in Australia  website .
• Avoiding Inhomogeneity in Percentile-Based Indices of Temperature Extremes , Zhang et al, (2004)

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Disclaimer

• Information provided in the AACI does not necessarily represent those of either the Institute of Actuaries of Australia (the 'Institute'), its members, directors, officers, employees, agents or that of the employers of aforementioned groups.
• The Institute and the employers accept no responsibility, nor liability, for any action taken in respect of the information provided in the AACI.

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Individual weather station data from the Australian Bureau of Meteorology (BoM) was relied on to construct the AACI with the aim of ensuring the data:

• had history going back to 1981, which is the start of the reference period; and
• was measured consistently over time (or had been homogenised by BoM as discussed below).

The weather station data from the BoM was reviewed for reasonableness, detailed analysis was not undertaken. Therefore, reliance was placed upon this source to provide accurate and complete data information.

More specifically:

• The temperature measures are based on the 112 ACORN-SAT stations. This data has been homogenised by the BoM to ensure consistency over time.
• The rainfall data is based on all weather stations across Australia that collect rainfall data (around 2,000 stations).
• The wind data is based on 38 stations that are thought to provide the most reliable wind data, noting that wind measurement is inherently more uncertain.
• The sea level data is based on 16 tide gauges around the country and are taken from the BoM’s Baseline Sea Level Monitoring Project.

About the Bureau of Meteorology (BoM)

The BoM has been collecting weather data from all around Australia since its inception in 1906. Some discontinuities and inconsistencies occur due to changes in technology, instruments, location, or environment. However, for certain stations and time series, the BoM has put considerable effort and resources into homogenising the data to ensure consistency through time. This process is widely acknowledged to be state-of-the-art and has been implemented for a subset of the station data. The ACORN-SAT data covers 112 stations across Australia for temperature. The locations of these stations give relatively good coverage across the regions used in the AACI.



For more information on the data and the development of the AACI see  Design Documentation .