Our research was motivated by how urban areas are often hotter than their rural surroundings, a phenomena known as the urban heat island effect. If we want to understand how urban heat islands are affected by coastal breezes, air flows coming from further inland or weather phenomena like heatwaves and the interaction between these different processes we need to use atmospheric models that are fit for purpose that can ‘see’ the complexity of our cities.
Our research aimed to do just that and uses Sydney, Australia’s largest city, as a test case for our new configuration of the Weather and Research Forecasting model run at a very high resolution of 800 m with a new urban classification scheme that describes the complexity of Sydney’s built environment.
Our results show that heatwaves often start with a hot continental flow over the Blue Mountains descending into the Greater Sydney region and that it gets stuck, leading to temperature differences across the city exceeding 15 ˚C. The urban environment on average adds about 1˚C of heat in the lower atmosphere, but over heatwave periods this can exceed 10˚C and also impact the Blue Mountains area when sea breezes act to push the heat further inland.
The level of detail we can see from these high-resolution simulations is so high that we can really interrogate the role of local breezes to either enhance or dissipate heat and this capability is the first step towards building an understanding of how our cities will need to adapt to climate change. You can see the full video and transcript here.
- Paper: Hirsch, Annette L., Jason P. Evans, Christopher Thomas, Brooke Conroy, Melissa A. Hart, Mathew Lipson, and William Ertler. “Resolving the Influence of Local Flows on Urban Heat Amplification during Heatwaves.” Environmental Research Letters 16, no. 6 (June 2021): 064066. https://doi.org/10.1088/1748-9326/ac0377.