Satellite Imagery vs. NowCast

At the beginning of July 2022, the Hawkesbury-Nepean catchment, located on the New South Wales Central Coast, Australia, began to flood.??

Major flood warnings were issued by the Bureau of Meteorology for Windsor with flooding likely to exceed the recent significant flood of 12.92m in March 2021. Access to credible, accurate and most importantly, timely data is critical at times like this to enable decision making, prevent damage and save lives.??

The Hawkesbury River peaked at 10am on 5th July 2022 at the Windsor P.W.D station with a river height of 13.94m, a bit over a metre higher than the March 2021 event.?

Satellite Imagery is frequently used in disaster management settings. However, the difference between FloodMapp’s NowCast and PostCast products and the limitations of satellite imagery is something we should talk about.??

For the event at Windsor, this satellite product captured the flood event at 10am on the 8th July 2022.??

By this time (three days after the peak), the water had already begun to recede and was almost 5m lower than the actual flood peak.?

What does this mean for emergency management decision making??

• An understanding of the impacted area was only ascertained three days after the flood peak.?
• The flood impact did not capture the event scale, as waters had already receded 5m.??
• Response decisions such as managing evacuations, road closures and disruption to services could not be based on a known extent of impact, as the event unfolded.?
• Recovery decisions could not be based on known impact extent for three days post event, leading to increased stress, confusion, support requirements and a delay in infrastructure restoration, and??
• In the event satellite is captured at the peak, cloud cover and other capture issues may result in low resolution images or complete lack of capture.?

This highlights the benefit of FloodMapp’s models.??

Our NowCast and PostCast captured and recorded this flood event as it unfolded in real-time.??

NowCast maps the current flood impact area and is updated hourly with the most recent data available, while PostCast maps the peak recorded flood impact area every 12 hours.?

This delivers timely situational awareness to emergency managers to improve response during and after a flood event.??

That being said, satellite imagery is an absolutely essential data collection tool and is very useful for validating our models?

However, it has limitations during an event compared to real-time flood modeling intelligence and therefore shouldn’t be solely relied upon in an unfolding emergency.?

The first image is a snapshot of what the satellite captured (dark blue) compared to what the NowCast product recorded at the corresponding time (light blue) when the river was at 9.1m. This shows accuracy and consistency between the two platforms.?

The second image shows a time series of how NowCast modelled the flood event (light-dark blue depth shading), peaking at 13.94m, compared to what the satellite captured (dark blue) at a river height of 9.1m.??

During a disaster, emergency managers and agencies don’t have time to wait for a satellite to orbit back to the correct location to provide updated information.??

They need to make crucial decisions in the here and now and that’s why FloodMapp NowCast and PostCast are essential.??

Learn more about it here: https://www.floodmapp.com/nowcast ??