Variability and trends in temperature and precipitation extremes

The severe flooding and bushfires in recent times have been a pertinent reminder of the risks our society faces from extreme weather events.

The Bureau of Meteorology provides information about the risks of extreme heat or rainfall occurring, based on historical occurrence as well as short range weather forecasts. These climatological risks can be specified in terms of Annual Exceedance Probability or Average Recurrence Intervals.

Conventional definitions of risk are based on the notion that the likelihood of extremes does not change over time. However, in the presence of modes of climate variability – such as the El Niño Southern Oscillation (ENSO) – and climate change this assumption of stationarity is no longer valid.

BOM’s analysis of trends and variability of extremes in temperature (maximum and minimum) and precipitation is based on a recently completed high-quality dataset. We have used extreme value distributions to assess trends over the period 1910 to 2009 and to explore the effects of ENSO on temperature and rainfall extremes. Similar analyses could be applied to other sector-relevant variables and indices.

The key findings included – To avoid spurious identification of trends in extremes, the analyses have to be based on homogenised data. – Depending on the variable, the effects of ENSO can be of a similar magnitude as long-term changes in extremes and climate change may lead to an intensification of heat extremes under El Niño. – There is a general tendency for shortened return periods when analysing high maximum temperatures but with significant regional deviations from this pattern. – Trends in low minimum temperatures are typically stronger than in high maximum temperatures.

The Australian & New Zealand Disaster and Emergency Management Conference  would like to thank Ms Doerte Jakob, Manager Hydrometeorological Advisory Services, Bureau of Meteorology for presenting this paper at the last conference held May 2013 at the Mercure Brisbane.  The conference looks forward to reconvening in May 2014 at the QT Surfers Paradise.  Abstracts are now open and you can submit an abstract by clicking here.  Or you can listen to presentations fro the last event by clicking here.