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Rain radar estimates size of floods

Using rain radar to estimate the size of flood events is a reliable approach. That’s according to a group of specialists at the 2016 Water New Zealand Stormwater Conference.

Understanding the timing and location of extreme rainfall is one of the most important parts of stormwater flood management. In most urban settings in New Zealand, city authorities make use of rain gauges to understand rain events. Often, understanding rain events is accomplished by classifying rainfall according to an average recurrence interval (ARI).
Rain gauge networks take point samples of the continuous spatially varying rain field and it is difficult to know if the heaviest rain has fallen on a rain gauge or fallen elsewhere in a catchment.
This rainfall variability can lead to large biases in determining ARI statistics for individual events when using rain gauge data, which in turn makes it difficult to assess the performance of infrastructure which may have been designed with a particular recurrence interval in mind.
Using Rain Radar to Estimate the Size of Flood Events presents a methodology for preparing rain radar data from the Auckland Metservice radar to allow generation of spatially continuous ARI maps, and demonstrates how the data can be used to gain understanding of the cause of flooding events for a test case.
Luke Sutherland-Stacey is an environmental scientist at Sutherland-Stacey Consultants. He specialises in measurement and quantification of changes in rapidly varying systems. Current work focuses on quantification of rainfall with radar for sewer and stormwater modelling applications.
Tom Joseph is a technical director at Mott Macdonald providing technical support and strategic guidance to a team of computational modellers, data scientists and software developers. His current focus is the innovative delivery of technical content to non-technical users through web-based technology.
Geoff Austin is a professor of physics at Auckland University’s Faculty of Science.
Nick Brown is stormwater flood planning manager at Auckland Council.

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