Remarkable! A new study by Ashcroft, Karoly and Dowdy pieces together an extraordinary 178 years of rainfall data from Sydney, Melbourne and Adelaide. This is a rare study that brings in much older data, looking at trends and extremes. This is pretty much the ultimate long term rainfall paper for South East Australia. Henceforth, there shalt be no more headlines about “unprecedented” rainfall or area’s drying out “due to climate change” unless an event rates against this data…
Australia – a land of floods and droughts:
- Rainfall goes up and down in long ongoing cycles or change, but no obvious trend that matches the sharp rise of CO2 in the last 30 years. It’s almost like CO2 has no detectable effect…
- The worst extremes were for the most part — long ago — particularly in the 1840s (assuming those records are reliable).
- Almost nothing in the last 30 years is unusual or unprecedented despite humans putting out 50% of all our CO2 since 1989.
- These charts show how misleading it is to use graphs that start in 1970 (or even in 1910) and declare that the recent changes are meaningful, or caused by CO2.
The researchers also use newspaper archives to describe these wild events. Some extracts below and the three key graphs. Normally this would be forgotten history, so it is excellent to see these old records being studied. — Jo
Sydney’s wettest year was 1950, driest year was 1849
Sydney’s wettest year occurred in 1950, while the driest year was recorded in 1849. Two very wet events for Sydney are apparent in the early 1840s — one in April 1841 when 20.12 inches (511 mm) was recorded at Port Jackson, and another in October 1844 when 20.41 inches (518 mm) of rainfall was observed at South Head in one day and night on the 15th– 16th. The Government Gazetteabstract for April 1841 described the deluge as “a most violent storm of rain”, and The Sydney Gazette reported extensive damage to buildings and roads as a result of the downpour (The Sydney Gazette, 1 May 1841, page 2, and 4 May 1841, page 2, available at http://nla.gov.au/nla.news-article2553198 and http://nla.gov.au/nla.news-article2553217).
Rainfall trends, cycles, Australia, Sydney, Graph, 2019, 1840 – 2020. Official caption: Fig. 3. a-c) Annual Rtot, Rx1day, RD and SDII values for Sydney, Melbourne and Adelaide, 1839–2017. Mean values for the whole period are marked in dotted horizontal lines, and 10-year moving averages of Rtot, RD and SDII are shown in light grey, plotted on the centre year of each 10-year period.
Abbreviations: Rainday counts (RD), monthly rainfall totals (Rtot), and highest daily rainfall (Rx1day).
The Simple Daily Intensity Index (SDII): the amount of rainfall received divided by the number of raindays recorded over a month and year.
Melbourne – wettest year and day was 1849
The Millennium Drought stands out as the driest period in the complete record, as noted in other studies of climate change in the region (Hope et al., 2017). The driest year occurred in 1967, at the start of three-year period of dry conditions (Fig. 3b).
Periods of wet conditions, such as the 1950s, are also associated with rainday increases. The wettest year in Melbourne’s history seems to have occurred in 1849, and included the wettest day in the extended record, when 7 inches (177 mm) was recorded on the 27th of November. The Government Gazette table reported rain from the 25th to the 28th of that month, with gales on the 27th. Newspapers at the time wrote that the event caused “Appalling Destruction of Life and Property”, claiming that the Yarra River “attained an unprecedented height” on the 28th (The Courier, 8 December 1849, p 2, available from http://trove.nla.gov.au/ndp/del/article/2964223).Flooding killed several residents and thousands of sheep, creating havoc for much of the settlement (The Courier, 8 December 1849).
Rainfall trends, cycles, Australia, Sydney, Graph, 2019, 1840 – 2020
Adelaide — wettest day was 1925
The wettest Adelaide day occurred on 6 February 1925, when 141.5 mm of rainfall was recorded in 24 h to 9am on 7 February due to a severe thunderstorm. Newspaper accounts at the time reported a “Tropical Downpour in Adelaide: A record fall of over five inches in two and a quarter hours” that had the “streets running like rivers”…
Adelaide rainfall (Fig. 3c) displays prolonged wet periods in the 1850s and 1920s, with dry periods apparent during the turn of the 20th century and the 1960s. The wettest year occurred during 1992 due to a very wet austral spring (seasonal analysis not shown), while the driest year occurred in 1967.
Rainfall trends, cycles, Australia, Sydney, Graph, 2019, 1840 – 2020
Abstract
The cities of Melbourne, Sydney and Adelaide are home to almost half of the Australian population, and are often exposed to extreme rainfall events and high year-to-year rainfall variability. However the majority of studies into rainfall in these cities, and southeastern Australia in general, are limited to the 20th century due to data availability.
In this study we use rainfall data from a range of sources to examine four rainfall indices for Melbourne, Sydney and Adelaide for 1839–2017. We derive the total rainfall, number of raindays, wettest day of the month and the simple daily intensity index for each city over the past 178 years, and find relatively consistent relationships between all indices despite potential data quality issues associated with the historical data. We identify several extreme daily rainfall events in the pre-1900 period in Sydney and Melbourne that warrant further examination as they appear to be more extreme than anything in the modern record.
We find a moderate and relatively stable relationship between El Niño–Southern Oscillation (ENSO) and annual variations of total rainfall and the number of raindays at all three cities over the research period, but no relationship between ENSO and the annual wettest day, in agreement with other studies using shorter time series.
Conclusion
This paper describes rainfall in three of Australia’s largest cities for the last 178 years using several mean and extreme rainfall indices. Combining historical daily observations and summary tables back to 1839 with modern records, we have been able to explore not only mean rainfall, but the occurrence and intensity of the extreme rainfall events for Melbourne, Sydney and Adelaide. Extreme rainfall events are likely to be associated with flooding and damage, noting that flood risk in cities is largely due to rainfall rather than other factors, such as soil moisture, which are important in other areas.
Issues with data quality and changes in observation location make it difficult in some cases to determine the accuracy of the absolute rainfall totals recorded. For example, the statistical differences between the historical and modern data for Melbourne and Sydney appear to be largely due to several extreme events in 1840–1860 period. Given the good agreement between the instrumental and documentary information, these events are undeniably extreme, but further examination could potentially help determine how accurate the absolute rainfall observations are.
h/t Willie
REFERENCE
LindenAshcroftabDavid J.KarolyacAndrew J.Dowdyb(2019) Historical extreme rainfall events in southeastern Australia, Weather and Climate Extremes Available online 10 May 2019, 100210