difference in D0 for comparing ground and tree air temperature at one position

[drinky fan]

Hi everyone,

Hope this email finds you well.

I want to compare air temperature between tree (height=1m) and ground (height=0.01m) at a single position.

Firstly I want to keep all parameters the same except Usury. But due to my D0 is set to 0.6 (according to 0.6 * canopy height), the error return "local height can't lower than D0" when I simulated ground environment. I wander whether it makes sense if I adjust D0 to default (0) for the ground environment and compare it with output in tree environment with D0 of 0.6.

I also want to know that whether soil temperature in 0cm can represent ground air temperature well. Because I lack soil temperature data, I can't validate its accuracy.

Thank you for your time and help.

Sincerely,

Junqi

[NicheMapR]

Hi Junqi,

Good question. This part of the model relates to the complex topic of boundary layer dynamics - how the objects in the landscape alter the turbulence and the way this affects convection and wind speed/air temperature profiles. 

The calculation of the air temperature profile requires knowledge of the ground (surface) temperature and predicts the profile from the roughness height/zero plane displacement height up to the reference height, but not below.  The soil surface temperature D0cm is indeed the ground temperature. Have a read of Campbell and Norman 1998 Ch. 2 and 5 for the theory. NicheMapR's microclimate model isn't really set up at present for modelling conditions under a forest canopy (see Ilya Maclean's microclimc for what's involved). 

If your habitat is relatively open, I would suggest you either don't use the D0/ZH parameters and set the roughness height to what is most relevant from the help in the model (smooth desert is 0.0003, closely mowed grass may be 0.001, bare tilled soil 0.002-0.006, current allowed range: 0.00001 (snow) - 0.02 m) or set D0/ZH based on the height of the sub-layer of vegetation (grass/shrubs).

You will need to do some kind of interpolation between the surface temperature (soil$D0cm) and the temperature just above the roughness/zero plane displacement height if you want temperatures below  D0/RUF. Overall you should be aware that the microclimate model is not specifically designed to be able to answer the detailed question of how a single tree or sparse trees in a habitat would alter air temp/wind profiles in the trees. In such cases I would use D0/ZH or RUF based on the general landscape and simulate the tree environment as shaded conditions (based on the canopy cover) with Usrhyt set to <= Refhyt.

Hope that helps.

All the best,
Mike

[drinky]

Thanks for your explanation! It really clarifies my misunderstanding. My interest of habitat is spare shrubs in a hill, and now i know that i should use the grass height as the canopy height rather than shrub height.

Cheers,

Junqi

NicheMapR <nich...@googlegroups.com> 于2025年10月20日周一 06:22写道：

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