Hi Joe,
I can provide a little more detail on a couple of Roy’s answers!
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The Natural Capital Project provides a Kc calculator (linked here: http://data.naturalcapitalproject.org/invest-data/Kc_calculator.xlsx) that can help fill in data gaps from the Allen et al. 1998 report. It isn’t perfect by any means, but can help adapt Kc values to more urban-centric land uses.
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If you are looking to dive into a bit of the literature on this air temperature blending distance, here are a couple of studies out of Wisconsin in the US that served as sources for the recommended 500m:
Schatz, J., & Kucharik, C. J. (2015). Urban climate effects on extreme temperatures in Madison, Wisconsin, USA. Environmental Research Letters, 10(9), 094024. https://doi.org/10.1088/1748-9326/10/9/094024
Schatz, J., & Kucharik, C. J. (2014). Seasonality of the Urban Heat Island Effect in Madison, Wisconsin. Journal of Applied Meteorology and Climatology, 53(10), 2371–2386.
Hope this helps, and good luck with the model!
Cheers,
Chris