The changing nature of risk from climate extremes

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In everything we do we have to deal with risks. Knowing about the nature of risks will affect the decisions we make in our day-to-day lives. These risks may change over time: the risk of falling asleep while reading an article will depend on how interesting the article is but also on how late in the day it is and how tired you are.

Our recent paper deals with risks resulting from weather and climate extremes and how they change over time. This is a complex topic. To make sure our analyses and results are accessible to a general audience, we have opted to use simple techniques and some illustrations to summarise observed changes in the extremes of two meteorological variables: temperature and precipitation.

Unsurprisingly, the risk for extremely high temperatures increases over time. Obviously, increasing temperature extremes at the hottest time of the year will be felt more keenly, so it is important to assess which seasons are most affected. We found that significant long-term increases in the highest maximum temperatures are typically found for winter and spring. But for summer and autumn, one needs to account for the marked regional nature of changes in high maximum temperatures. Sites located in the north of the continent (with wet summer or summer dominated rainfall regimes or arid conditions) exhibit a predominant decrease in extreme maximum temperatures, while sites further south (with uniform or winter rainfall regimes) typically exhibit an increase in extreme maximum temperatures for these seasons.

In contrast to long-term increases in temperature extremes, there is little evidence for a consistent direction of change in daily rainfall extremes. However, our results indicate that there might be a shift from extreme autumn/winter precipitation to spring precipitation. There is also strong evidence for the effect of ENSO on daily rainfall extremes, and this effect is particularly strong for spring.

What does this mean? It is crucial to develop an understanding of the purpose of assessing risk and in particular the relevant timeframes. This understanding will define what data are best suited for the assessment: historical information, multi-week, and seasonal forecasts or climate model output. In assessing the likelihood of hazards resulting from weather and climate extremes, one needs to consider the modulation of these extremes due to both long-term change and climate variability. Our results clearly illustrate that both effects need to be considered, but the relative importance of their effect depends on the variable or index.

Article: ‘Variability and long-term change in Australian temperature and precipitation extremes, Jakob, D., and Walland, D., Weather and Climate Extremes, doi.org/10.1016/j.wace.2016.11.001

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