In November and December of 1829, the Perth region was battered by “strong squalls” and a “very fresh wind and boisterous sea“. The gale-force winds pushed the H.M.S Success aground, and was part of a succession of wind-related shipwrecks which contributed to “failure and famine” difficulties in the colony of Swan River, Western Australia.
How can we learn more about the conditions that tend to lead to these kinds of gale-force winds in the Perth region?
The above extract from ‘Results of Rainfall Observations made in Western Australia’, is an important historical document that can give us some information. Although we don’t have instrumental weather observations for Perth in November 1829, we have near-continuous daily observations from 1830 onwards that provide a picture of conditions experienced by 19th century settlers.
UNDERSTANDING PERTH’S HISTORICAL CLIMATE
In March 2021, our team published a paper compiling the daily weather observations for the Swan River colony (modern-day Perth), from 1830 to 1875. Our current citizen science project aims to rescue Perth’s daily weather from 1880 to 1900 to help link the Swan River records with the modern Bureau of Meteorology’s records up to the present day.
While the weather observations in historical records are highly valuable for climate research, it’s important to note that they were not taken in the exact same way as records kept by the Bureau of Meteorology (BoM). That’s why we compare the daily historical observations to the BoM’s modern daily data to see how things line up.
We can use wind direction to verify other observations like temperature, pressure and remarks. This helps us to have multiple lines of evidence when reconstructing past weather events.
SEVERE STORMS IN PERTH
When we analysed Perth’s climate from 1830 to 1875, we looked at the general wind directions as well as ‘stormy conditions’, such as a drop in temperature and pressure, and remarks on storms or rain. We found in the historical record that wind and storms typically came from the southwest.
The BoM’s modern daily record confirms that storms in Perth since 1944 do generally come from the southwest, coming up from Antarctica through the southern Indian Ocean. There are also occasional cyclonic storms coming from the northwest, which are often associated with degrading tropical cyclones.
In our paper, we compared modern ‘wind roses’ from the BoM’s data (Perth airport, 1944-2016) with historical wind roses (Swan River, 1830-1875). The similarities between the modern and historical observations confirmed that we reconstruct past storm conditions using historical wind observations from historical records. We also showed how historical temperature, pressure and wind direction observations fluctuate during a typical onset and decay of storm events.
HEATWAVES IN PERTH
The typical summer conditions in the Perth region are easterly winds that bring hot, dry conditions. There’s also a welcome relief to the summer heat provided by the ‘Fremantle Doctor’, a cool, gentle southwesterly sea breeze often arriving in the afternoon, bringing cooler air temperatures.
During a heatwave, instead of the air coming from the ocean, the air is flowing over the land from the northeast or east. So, to verify conditions experienced during past heatwaves, we looked at the variations in historical pressure and wind observations to see if they were comparable with the typical conditions that cause modern heatwaves.
Our analysis showed the historical temperature, pressure and wind direction recorded the dynamical conditions typically experienced during modern heatwaves. We observed the prevalence of northeasterly winds that increase temperatures in Perth, as seen in modern records.
We can use the wind observations as a way to help verify the temperature and pressure observations in journals that in Perth’s case are up to 191-years old. And the direction of the wind observations are useful as a comparison on extreme weather events, such as really stormy days, and during heatwaves.
THE CASE FOR RECOVERING MORE HISTORICAL CLIMATE DATA
The city of Perth in Western Australia has experienced a significant decline in winter rainfall since 1970, likely caused by a southward shift in the storm track. This means that rain-bearing systems that used to cross the land are now occurring further southwards. Part of our research looks at how these kinds of shifts in weather patterns compare to the long-term climate. But to do this, we need as many consistent, long-term, daily weather observations as possible – which is why we need your help!
By recovering the ‘wind direction’ observations in our current citizen science project from 1880 to 1900 for Perth, we’ll have a more complete picture about the temperature, pressure and wind direction during the 1800s, which we can again compare to the modern records.
Start transcribing the Wind Direction workflows on Zooniverse, here: https://www.zooniverse.org/projects/caitlinhowlett/climate-history-australia/classify