Flooding in NSW has forced the evacuation of at least 18,000 people, with areas on the mid-north coast receiving as much as 890mm of rain in the past week.
The flooding on the mid-north coast is the worst since 1929, according to the emergency services minister, David Elliot.
Here, you can see the flooding and rainfall in context with historical data (or at least as much as is available), with some areas breaking longstanding records for river heights.
This chart shows the maximum river height in metres for each day in 2021 overlaid on the daily river height for as many previous years as were available from WaterNSW’s water monitoring network. You can use the drop-down menu to switch locations.
You can see, for example, how the Hastings River in Port Macquarie has peaked at 12.1m, higher than the February 2013 floods:
This is a level not seen since 1888, according to the Port Macquarie News.
Here’s the view of rainfall in the same format, which is good for showing days with extreme rainfall against historical extremes. You can hover or tap the lines after the animation is finished to see which year the data is from.
However with flooding, the issue is not necessarily a single heavy day of rain, but sustained heavy rainfall over time.
Here, you can see the cumulative daily rainfall for 2021 against the historical trend. This chart takes all the available rainfall data and plots the median rainfall for a given day of the year, and also lines for the 10th percentile (below this line would be the 10% of driest days for this location) and the 90th percentile (above this line would be the 10% of wettest days for this location).
Where the 2021 line is above the median, that means it is wetter than normal for that day of the year. When the line is above the 90th percentile, that means it is much wetter than normal – it is wetter than 90% of all of the values for that day of the year in the historical dataset.
This shows, for example, that Katoomba in the Blue Mountains was tending towards a relatively normal year until mid March, and that rainfall in Port Macquarie began to get unusually wet from late February onwards.
I’ll be updating these charts with more data as it comes in, and will add more sites once the data processing is done. If you’d like to suggest a location for inclusion that has a good amount of data either in the BoM’s database here or WaterNSW’s database here you can email me at firstname.lastname@example.org.