Past and future trends in Australian floods: what are the causes?
Johnson, F., C.J. White, A. van Dijk, J. Evans, D. Jakob, A.S. Kiem, M.Leonard, A. Rouillard and S. Westra
MODSIM2015, 21st International Congress on Modelling and Simulation. Modelling and Simulation Society of Australia and New Zealand, Gold Coast, Australia, 29 November – 4 December 2015.
The possibility of changing flood hazards due to climate change is an issue of concern for
engineers, governments and emergency services. However it is not yet clear how flood hazard will change
and how these changes may vary across Australia. Here we approach these questions by considering the
complex interactions between flood-causing variables. This is achieved by synthesizing existing research on
the trends and likely changes in the causes of floods. These causes include the possible changes to
meteorological variables, in particular extreme rainfalls, as well as impacts of changing catchment conditions
including catchment wetness and land use modifications due to vegetation changes and/or urbanization.
There has been research into trends in daily rainfall extremes around the world and for Australia but less
work on sub-daily rainfall. Australian daily rainfall extremes show limited evidence of trends when the
annual maximum series is considered although there is significant variability in these time series and changes
in seasonality are not accounted for in this type of analysis. Sub daily rainfalls show clearer evidence of
generally increasing trends. The interaction between these generally increasing trends and changes to
catchment wetness which are more likely to be linked to annual rainfall and evaporation trends is a question
of particular interest.
An issue of concern is how to separate trends from other cycles of variability introduced through large scale
climate drivers. Improved statistical methods are required to separate these interactions both in rainfall and
more importantly in the flood hazards. Promising work from detection and attribution studies on the
likelihood of individual extreme events needs to be translated into methods that can assess the likelihood of
trends and the possibility of detecting these trends.
Here the focus is on how the trends in each of these aspects can be combined together to better understand
the observed changes in flood risk. Using this improved knowledge, projections of changes in flood-
producing mechanisms can be combined to establish likely future flood risk. Open research questions have
been identified that could be addressed by the Australian research community over the next 5 to 10 years
• The need for robust future projections of extreme precipitation over daily and longer durations from
a large ensemble of climate projections at resolutions (~3 – 10km) that can capture important
phenomena such as east coast lows, orographic effects, bands on thunderstorms etc.
• Work in extending the findings from convection-permitting climate models to inform engineering
practices that depend on sub-hourly and sub-daily extremes.
• Common frameworks for undertaking catchment scale assessments of future flood risk to allow
findings to be translated and regionalized.
This page is maintaind by Jason Evans |
Last updated 31st January 2013