An analysis of historical South-East QLD rainfall and catchment levels.
The purpose of this study was to analyse historical total/average rainfall amounts and dam catchment levels for South-East Queensland.
This study was conducted in relation to analysing potential trends over multiple significant weather events, including the 2011 Brisbane Floods and the recent and ongoing 2022 Eastern Australian Floods.
The investigation was split into two areas:
- Calculating and analysing total/average SEQ rainfall from 1899–2022 and,
- Calculating and analysing SEQ dam catchment levels from 2017–2022.
The wide time-span of 1899–2022 was chosen to provide context of recent weather events amongst historical SEQ rainfall data.
Similarly, the time-span of 2017–2022 was chosen to highlight and identify potential trends in relation to the ongoing 2022 Eastern Australian Floods.
For this study, the Alderley Weather Station (Station 040224) in Brisbane's inner-north was chosen to analyse total/average historical rainfall.
As is evident in the charts, there was a significantly reduced amount of rainfall during the period of 2005–2010, which coincided with the QLD Government's introduction of a series of water restrictions.
The chart also shows a trend in the gradual increase of rainfall towards the end of this period, which ultimately led to the easing of water restrictions. However, this trend also shows an ongoing increase in rainfall during this period, which may correlate to the region's flooding events in 2011.
Conversely, there is a downward trend towards the latter-half of the decade where total rainfall gradually eased. However, on 28 February 2022 a new single-day rainfall record was broken, with the region receiving 344 mm of rain in just one day – beating the 114-year-old record of 308 mm set in March 1908.
The above chart shows a clear positive trend in the increase of average monthly rainfall during summer compared to winter. This seasonal variance also correlates with the region's humid sub-tropical climate and tendency to receive more rainfall during the Queensland 'wet' season (November–March).
For this study, the total SEQ Water Grid was analysed to investigate total capacities, current volumes and operating statuses of SEQ catchments. The figures in the chart below were accurate as of 9:00am 7 March 2022.
| Catchment Area | Capacity (ML) | Current Volume (ML) | Percent (%) | Current Status |
|---|---|---|---|---|
| Atkinson Dam | 30401.0 | 30742.0 | 101.12% | Over Capacity |
| Bill Gunn Dam | 6947.0 | 6629.0 | 95.42% | Near Capacity |
| Borumba Dam | 46000.0 | 48022.0 | 104.40% | Over Capacity |
| Cedar Pocket Dam | 735.0 | 769.0 | 104.63% | Over Capacity |
| Cooloolabin Dam | 8183.0 | 8250.0 | 100.82% | Over Capacity |
| Enoggera Dam | 4262.0 | 4445.0 | 104.29% | Over Capacity |
| Ewen Maddock Dam | 16587.0 | 17246.0 | 103.97% | Over Capacity |
| Gold Creek Resevoir | 810.0 | 952.0 | 117.53% | Over Capacity |
| Hinze Dam | 28.0497 | 338595.0 | 108.97% | Over Capacity |
| Lake Baroon | 61000.0 | 61851.0 | 101.40% | Over Capacity |
| Lake Clarendon | 24276.0 | 8599.0 | 35.42% | Low Capacity |
| Lake Kurwongbah | 14192.0 | 14721.0 | 103.73% | Over Capacity |
| Lake Macdonald | 8018.0 | 8354.0 | 104.19% | Over Capacity |
| Lake Manchester | 26217.0 | 26485.0 | 101.02% | Over Capacity |
| Tingalpa Resevoir | 13206.0 | 14899.0 | 112.82% | Over Capacity |
| Little Nerang Dam | 6705.0 | 6793.0 | 101.31% | Over Capacity |
| Maroon Dam | 44319.0 | 44457.0 | 100.31% | Over Capacity |
| Moogerah Dam | 83765.0 | 88714.0 | 105.91% | Over Capacity |
| Nindooinbah Dam | 208.0 | 275.0 | 132.21% | Over Capacity |
| North Pine Dam | 214302.0 | 144067.0 | 67.23% | Low Capacity |
| Poona Dam | 655.0 | 586.0 | 89.47% | Near Capacity |
| Somerset Dam | 379849.0 | 297873.0 | 78.42% | Near Capacity |
| Wappa Dam | 4694.0 | 4731.0 | 100.79% | Over Capacity |
| Wivenhoe Dam | 1165240.0 | 1120710.0 | 96.18% | Near Capacity |
| Wyaralong Dam | 102883.0 | 106317.0 | 103.34% | Over Capacity |
Which, when visualised, reveals an unsuprising trend in the current status of a majority of SEQ's catchment areas.
The following figure charts total catchment levels during the period of 2007–2022, indicating the surge in total rainfall in the region in early 2022.
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It must be noted that the upward trend in total rainfall during the 2010–2011 summer period was not the sole variable or cause of the 2011 Brisbane Floods. This significant flooding event was caused via a mixture of heavy rain over the period and the release of excess water from the SEQ Water Grid, as outlined in a 2011 Macquarie University report.
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There is a potential data anomaly/outlier during the early 1900s and 2000s which may alter findings, albeit insignificantly.
Bureau of Meteorology, 2022, Weather stations, http://www.bom.gov.au/climate/data/stations/
SEQ Water, 2022, Dam Levels, data, https://www.seqwater.com.au/historic-dam-levels
SEQ Water, 2022, Historic Dam Levels, data, https://www.seqwater.com.au/historic-dam-levels
Van den Honert, Robin C., McAneney, J., 2011, The 2011 Brisbane Floods: Causes, Impacts and Implications, https://www.mdpi.com/2073-4441/3/4/1149/htm