It never rains but it pours: Intense rain and flash floods have increased inland in eastern Australia
This month, a coastal trough along the Queensland and New South Wales coasts and an inland trough resulted in unusually widespread flooding, triggering flooding in Sydney as well as inland.Inland, flash floods occur when intense rain hits small urban catchments, runs off roads and concrete, and flows into low-lying areas.
The result was localized extremely heavy rain, which led to the Warragamba Dam spilling and flood plain inundation in western Sydney.as a"black nor'easter," a term coined in 1911. These are characterized by a deepening coastal trough and upper-level low pressure systems further west, over inland eastern Australia. This term, mostly known in the marine fraternity, became less common during the 20th century. But it has returned.
In every case between 1957 to 1990, flash floods in Sydney were not linked to slower-forming riverine floods on the Nepean-Hawkesbury River system. When these rivers did flood during that period, they came from longer duration, less intense rain falling in the catchments, and largely from east coast lows. Now we're seeing something new.Flash floods are not new. What is new is where they are occurring. These sudden floods can now form well west of the Great Dividing Range.
Now that it's moving south, we have increasingly warm air over inland eastern Australia which can hold more moisture and result in heavy falls, even in the cooler months.