I have a few of questions about inputs into the urban cooling model.
Are there any general resources for Kc values per common/broad land cover classes. The Allen 1998 reference in the user guide seems to mainly provide very specific crop type Kc values. Where do the Kc values from the example dataset come from? How would you suggest determining a value for a simple land cover class such as “trees” or “mixed low vegetation” in a tropical climate for example?
The user guide states Kc values should be between 0 and 1, yet in Allen 1998 there are several higher than 1 (if I am looking in the right place). Why is this?
For the “blending distance” input, the user guide suggests a default value of 2000m. However, in the appendix table it then suggests 500m. Which is more suitable as a default?
I can provide some guidance to your questions, and @chris may be able to add more detail.
The Allen et al 1998 report indeed has an agricultural focus, but is the most extensive reference that we have found on Kc. It does list Kc values for trees, including in more tropical regions - e.g. category l. Tropical Fruits and Trees or category n. Fruit Trees. Many tree types have Kc values close to 1. For mixed low vegetation you could look at the ‘Forages’ category mixed with some types of bushes. Admittedly, this is not perfect, so if you do come across a better reference please let us know!
Thanks for pointing this out, we will need to adjust the wording in the user guide.
I suggest starting with the 500m value in the appendix that is based on the first studies we have used the model in. The 2000m is an artifact from an older version of the user guide, we need to update that. These values are not fixed, and the model may perform better with a different distance in your case study. I suggest to try different values to learn more about how the model responds in your case.
I hope this helps a bit. Your questions definitely help us clearing up some issues in the user guide.
I can provide a little more detail on a couple of Roy’s answers!
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.
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.