How do you calculate the heatwave threshold?

The maximum temeperature of each day of the year is compared to a threshold that is specific for that day of the year. This is the 90th percentile , calculated from all respective dates between 1961-1990. Since the temperature of a particular day is dependent on adjacent days, we also include a window of 7 days either side of the date we’re interested in. Leap days are also included. A heatwave occurs when three or more days in a row exceed their respective 90th percentile thresholds for maximum temperature.

Can heatwaves be measured in other ways?

The short answer to this FAQ is yes! The method used on this site is based on scientific research, and was chosen so that heatwaves could be readily measured from observational data, as well as being presented clearly. If you want to know other ways heatwaves can be measured, please don’t hesitate to contact us!

How can heatwaves occur in winter?

While we may not feel periods of longer than normal heat in colder months, these heatwave events, where temperatures are far above normal for these times of year, are very important for a variety of areas, in particular agriculture and ecosystems.

For this reason, Scorcher measures heatwave events throughout the year, not just in the summer months.

Where does the temperature information come from?

Heatwave information used at Scorcher accesses two types of temperature products, freely available from the Australian Bureau of Meteorology’s website. These are:

  1. Daily heatwave maps constructed from the Australian Water Availability Project data; and
  2. Temperature time series for each station from the high-quality ACORN-SAT network, which was first released by the Bureau of Meteorology in 2011.

Due to the publication of these data products, the heatwave information on Scorcher is generally delayed by 2 days.

Why are two types of temperature products used?

In order to create the map of current heatwave conditions, we need to use a gridded dataset that provides entire spatial coverage of the Australian continent. Station observations alone can’t provide this, and so this is why we use the Australian Water Availability Project product. However, if we want precise heatwave information for a particular location, station data from ACORN-SAT is the best possible source. Combining these two types of products means that we can give you a comprehensive picture of past and current Australian heatwaves.

Why are there gaps in the temperature records for some stations but not others?

Unfortunately, some stations are not continuous for the entire period that observations have been available in Australia (from 1910 onwards), due to various reasons that are out of our control. So, instead of discounting these stations altogether, we just present heatwave information on the data that we do have.

Why are there more stations in some areas but not others?

Australia is a sparsely populated country, and the location of the temperature stations reflects this. While other temperature sites may exist, we only use stations of the highest quality that are monitored and maintained by the Australian Bureau of Meteorology.

Is there a relationship between heatwaves and climate change?

Heatwaves have always occurred in Australia. However, since they are an extreme event their occurrence, by definition, is rare. As the background climate warms due to human activity, this increases the frequency and intensity of hot temperature events, like heatwaves. You can find more information about the relationship between average and extreme temperatures here .

Research conducted at the ARC Centre of Excellence for Climate System Science has detected an increase in the frequency of Australian heatwaves since 1950. Research is currently underway to deterimine how heatwaves may change in the future over Australia, as atmospheric greenhouse gases continue to rise due to human activity.

I can only see past heatwaves, there are no forecasts.

The purpose of Scorcher is an interactive tool for you to explore both recent and past heatwaves at 100 different sites across Australia. Scorcher does not have a forecasting capability, nor will it have this function in the future. If you want to find out more about heatwave forecasts and warnings, please visit the Australian Bureau of Meteorology's heatwave forecast service.