Previously unknown weather extremes discovered in new Adelaide record

Our analysis of recently transcribed historical data has picked up extreme events such as a week-long heatwave, bushfires, a dust storm, and severe storms that caused hail and flooding in 19th century Adelaide.

Citizen scientists transcribed newly discovered historical daily weather observations from 1843 to 1856 for the Adelaide region. 

The data show that 1847 was a particularly eventful year; with heatwaves in both February and December, and a significant storm in July. We also discovered that the winters of 1846 and 1847 were unusually wet. 

A week-long heatwave in February 1847

A major heatwave was discovered in the record from  20-26 February, 1847. Temperatures of above 40 °C were observed for seven days in a row, peaking at 41.1 °C on the 25th. 

The Adelaide Surveyor General’s Office daily weather record from February 1847 shows persistently hot temperatures from the middle to the last half of the month [Click here for a larger version]. Source: National Archives of Australia.

To verify our results, we checked to see if the heatwave was recorded in newspapers of the time. 

There was a plethora of published articles, explaining how the “intolerable”, “distressing”, “dreadful” and “unprecedented” hot weather had affected people in Adelaide in mid-February 1847. The Remarks in the Survey Office journals show two 9am temperatures of 37.7 °C, and a 6pm observation of 35 °C, indicating that the nights were likely to have been quite hot as well.

Several men and many children are reported to have died from the heat. Court proceedings had to be “unavoidably postponed”.  There were grass fires, other fires in the plains surrounding Adelaide, and also in the Mt Lofty ranges just 40km from the city. Even the newspaper staff had to cease working, stating they were “obliged to issue this copy in a curtailed form”. 

There were also reports of “clouds of dust” and “tempest-driven” dust, suggesting this heatwave was accompanied by a dust storm and/or strong, hot winds. Dust storms and bushfires would explain the numerous “hazy” Remarks in the Survey Office journals throughout this month.

Dry, with particularly wet winters in 1846 and 1847

We tallied the ‘Rain days’ collected by citizen scientists, based on the mention of rain in the Remarks of the Adelaide Survey Office journals. These observations  provide an overview of rainfall conditions experienced from 1843 to 1851 (unfortunately there were no comments noted after February 1851).

We developed the figure below to visualise the cycle of wet and dry periods. While we’d expect to see winter rainfall in Southern Australia’s climate, we noticed that overall the study period was fairly dry, with some noticeably wet winters in 1846 and 1847.

    Adelaide Rain Days, 1843-1851

Each stripe represents each day over the 1843-1851 study period. To categorise how wet each day was we looked at how often rain was mentioned each day. The red stripes show no or very light rain (either no mention or one mention of rain in the comments), yellow shows moderate rain (two mentions of rain in a day), and blue shows heavy rain or really wet days (more than two mentions of rain in a day).

The newspapers suggest that the winters of 1846 and 1847 were particularly wet. There are many reports of deluges of rain and hail that caused localised flooding and damage to buildings and bridges. There were also many descriptive accounts of the wet winters in Adelaide in 1846 and 1847, for example:

“The incessant and violent rains have swelled the mountain torrents to overflowing… in Adelaide on a Saturday afternoon… a storm so violent that not only were shingles torn from roofs… it literally rained upwards, as well as downwards.”
The South Australian, 22 June 1847.

The storm of July 1847

We found evidence of some significant storm activity in the Adelaide record, so cross checked the dates with reconstructed weather charts generated by the 20th Century Reanalysis. 

There has already been some thorough research on historical flood events in Adelaide starting from 1836, which includes a known flood in Adelaide on 22 July 1847. 

We do also know of some flooding events already in 1848 and 22 July 1847, as we noted in our own blog recently here.

The newly transcribed Survey Office daily weather record shows storm conditions from 20–25 July 1847 as reported in the newly recovered rain days, pressure observations and remarks. 

We looked at the 20th Century Reanalysis fields for these dates (image below), and identified a significant and persistent low pressure system (yellow and orange on the bottom row) located between Tasmania and New Zealand. You can also see that this low pressure system produced temperatures that were about 5 degrees cooler than average (top row). 

The 20th Century Reanalysis field indicates that there was a significant storm across the southern half of Australia and New Zealand in July 1847. The top row shows temperature, and the bottom row shows pressure. We can see there was a very big and strong cold front (blue and dark blue) that was likely produced by a persistent low pressure system (shown as yellow and orange with isobars very close together).

The comments in the Survey Office journals on 22 July, 1847, which are usually reserved for direct weather observations, found the flooding significant enough to note: “The bridges on the Torrens River carried away.”

Newspapers at the time described destruction of bridges due to river levels that were “higher than it has been for eight years”, as well as hailstones up to an inch in diameter. The South Australian newspaper reported that; “The weather has been most tempestuous; storms of thunder, lightning and rain such has never been experienced since the foundation of the colony”.

How we’ll use these new observations

These weather observations from the newly transcribed Adelaide journals will eventually contribute new Australian data into historical global databases such as the 20th Century Reanalysis.

The next step will be to merge this data with the observations of William Wyatt (1838-1847) and the existing data from the Bureau of Meteorology to try and develop a continuous daily weather record for Adelaide back to 1838.

Through this detailed understanding of extreme weather in the past, our society can better understand how to prepare for extreme weather in a warming world. Extreme weather events in the future are predicted to be even more frequent and intense than they were in the past.