Protecting people from floods requires many technical professionals to make good predictions and decisions.

Meteorologists predict the risk of extreme rainfall. Hydrologists translate this rainfall into predictions about what the flood will be like in terms of depth, flow and speed. Engineers design roads, bridges and buildings to cope with the likely conditions, while planners ensure new development is compatible with flood risks.

No step in this process is easy – and most are getting harder. Climate change is worsening flooding, because a hotter atmosphere can hold more water vapour which supercharges clouds. A hotter climate provides more energy to lift wet air high into the atmosphere, where it cools, becomes liquid and forms extreme rainfall. In Australia’s north, the intensity of heavy rainfall events has already increased by 10% since 1979.

While it is difficult to adapt to unpredictable rainfall events, we can improve our flood predictions. We focused on improving a common flood prediction technique called the Rational Method.

While simple to use, it can also get some things very wrong – such as underestimating flood peaks by 200%. To fix this, we worked with the developers of Arc Hydro, a popular software package used by stormwater and flood planners, to better describe how the shape of hillslopes affects floods. We hope this can help planners gain a better understanding of the true flood risks in specific areas.
Why do we need better flood predictions?
It’s particularly hard to predict the risk of extreme storms – like those that drove devastating flooding in parts of New South Wales and Queensland earlier this year – because for these storms, the past is not a good guide to the future. Those floods came from a “rain bomb” which dumped 60% of south east Queensland’s normal annual rainfall in just three days.

Managing flood risks is hard, given the cost of flood protection, evacuation and resilience in developed areas and challenges in restricting development in high-risk areas.

Read more: https://theconversation.com/our-flood-predictions-are-getting-worse-as-the-climate-changes-we-have-to-understand-how-hills-shape-floods-183820