At Watercom, we have advocated for climate change consideration in all stormwater and flood models for several years. Specifically, we have pushed for consideration of the 2030 rainfall multipliers in addition to the existing Bureau of Metereology (BOM) 2016 Intensity-Frequency-Duration (IFD) design rainfalls .
The mid-point of the existing BOM IFD rainfall data is 1990, yet the climate has already warmed about 1°C in the past 25 years (Lenssen et al. 2024)1.
And so, we are pleased to see the release of the updated Australian Rainfall & Runoff (ARR 4.2) Climate Change Considerations chapter. Under the latest guidance, a small urban catchment with a 1-hour critical duration should already include a +18% rainfall multiplier for 20302.
Looking ahead, depending on the trajectory of Shared Socioeconomic Pathway (SSP) emission scenarios for new projects, medium-term projections for 2050 suggest rainfall increases between 22% and 34%, while long-term projections for 2090 range from 23% to 77%2.
As an industry, it is crucial to start implementing these changes and we have set this in motion with the release of our free Climate Change Rainfall Modifier.
We also encourage authorities to mandate the inclusion of these considerations in stormwater and flood models to ensure resilience for the future.
1 Lenssen, N., G.A. Schmidt, M. Hendrickson, P. Jacobs, M. Menne, and R. Ruedy, 2024: A GISTEMPv4 observational uncertainty ensemble. J. Geophys. Res. Atmos., 129, no. 17, e2023JD040179, doi:10.1029/2023JD040179.
2 Ball J, Babister M, Nathan R, Weeks W, Weinmann E, Retallick M, Testoni I, (Editors) Australian Rainfall and Runoff: A Guide to Flood Estimation, © Commonwealth of Australia (Geoscience Australia), Version 4.2, 2019.
GISTEMP Team, 2024: GISS Surface Temperature Analysis (GISTEMP), version 4. NASA Goddard Institute for Space Studies. Dataset accessed 2024-11-04 at data.giss.nasa.gov/gistemp/.
