Forecasting heat wave severity

Hot and bothered - heat wave hits Australia in January (Reproduced with the permission of the Bureau of Meteorology)
Hot and bothered – heat wave hits Australia in January (Reproduced with the permission of the Bureau of Meteorology)

Heat waves are a feature of the Australian summer and they claim more lives each year than other natural events — bushfires, floods, and storms — combined. As the climate continues to warm due to the effects of climate change, heat waves are set to become more frequent, and potentially more deadly. So it seems a little odd that we haven’t had an accurate way of forecasting whether a heat wave is on its way, and more importantly, how severe an imminent heat wave might be. The Australian Bureau of Meteorology  (BOM) is currently piloting a heat wave forecasting system that will do exactly this — I wrote about the science behind the forecast system for Science (subscription required).

The system uses gridded climate data — rather than temperature data taken from individual weather stations — to produce a high-resolution map of forecast temperatures across Australia. It then compares temperatures at each map point with previous temperatures recorded for that point and asks two important questions: are the next three days in the hottest 5% of days compared to the past 30 years? How do those hot days compare to the month preceding them? This second question is essentially an acclimatisation factor. If it’s been relatively mild in the lead up to a heat wave, it’s going to hit harder than if people are already acclimatised to the searing heat. The final step — adding a measure of severity — is achieved by comparing these 3-day events with all previous heat waves from the past 50 years. A severe heat wave is one in the top 15 percent of heat waves within this period (see map). Extreme heat waves are even rarer, but also likely to have a far greater impact. Head over to Science to read more.

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