Modelling future extreme weather
Extreme weather is the sharp end of climate change. Aotearoa New Zealand is highly vulnerable to the impacts of extreme weather like flooding from heavy rainfall. Homeowners, the government and insurers are just some of those eager to know what the future holds in store.
New Zealanders need information on climate change at scales they can usefully use for their particular needs. Climate change information e.g. changes in temperature, precipitation and wind are needed to drive a range of onward modelling in the chain that, ultimately, links increased greenhouse gas emissions (and other aspects of human influence) to the eventual impact of interest for example crop growth or flood extent. Many of these impacts require their inputs at very local scales.
Due to the nature of extreme events and the computational expense of running climate models, it is
very difficult to extract information on extreme weather using traditional methods, as the number of
available model runs is typically fairly small.
By crowdsourcing computational power across the world, this project is running and analysing thousands of climate model runs to better understand future extreme weather in Aotearoa New Zealand.
- This project has produced a very large collection of climate model simulations for future +1.5°C, +2.0°C and +3.0°C worlds at a resolution of 50 km, an unprecedented dataset for New Zealand. The large number of model simulations means that the frequency of rare weather events can be counted directly, improving our understanding of the future frequency and intensity of extreme events.
- Analysing these large model ensembles, this project has evaluated statistical models to better extract extreme rainfall information from one-off, or small ensembles of model runs, with improved understanding of the way model parameters scale with increases in temperature.
- The current tool for understanding changes to extreme rainfall with climate change is HIRDSv4 (High Intensity Rainfall Design System). Currently, HIRDSv4 assumes that climate change will have the same effect on extreme rainfall everywhere across the country. This project is investigating regional differences in the climate change signal, and will offer insights and stakeholder-targeted guidance into how to interpret and use the HIRDSv4 data to take into account regional differences.
How this research is being used:
- This knowledge will contribute to the next generation of the HIRDS tool for understanding extreme rainfall.
- Where the results are robust, this project will offer New Zealanders good understanding of what we expect to happen in their region.
- In regions where there is high uncertainty, for example, due to complex topography, this work will identify priorities for future research.
In the media:
- NZ’s big dry and climate change: What’s the link? NZ Herald
- Climate change: Revealing its hand in today’s extreme weather NZ Herald
- Climate change doubles risk of extreme rainfall in Northland Stuff