# Is Bowen ratio an absolute indicator of land surface type based on the amount of heat transfer from the surface?

Bowen ratio (BR) is the ratio of sensible heat flux to latent heat flux, i.e.,

$$Q=Q_{s}/Q_{l}$$ where $Q_{s}$ is the sensible heat flux and $Q_{l}$ is the latent heat flux. It is an indicator of the amount of heat lost from the surface to the atmosphere. In water bodies, latent heat of vaporization is higher and hence the bowen ratio is less than one. In dry urban surfaces (e.g., buildings and asphalt roads), evaporation is lower and the bowen ratio is greater than one. The bowen ratio over different surfaces have different values.

Can we then identify the underlying surface roughness type based on the bowen ratio alone?

I am thinking of the latitudinal and altitudinal dependence of the heat flux regime. For example, assume that there are the same vegetation distribution at 1km above sea level (a.s.l) and 4 km a.s.l at different but relatively closer latitudes, then can they have the same bowen ratio?

My idea is that BR is not the right way of quantifying the type of surface roughness because the lower pressure and temperature at 4 km in the example above favors more sensible heat flux than latent heat flux which increases the bowen ratio and gives wrong signal that the surface type is bare soil or sand. Can someone explain why BR is used as a means of quantifying the surface roughness type?

Since $B=y\frac{\partial T}{\partial e}$ where y is the psych constant (~0.4 and really not a constant) it can be seen that the gradients of temperature and moisture, not the actual values, are the only two factors that matter in determining the Bowen ratio. Each plant essentially has a "specific Bowen Ratio" range where they are able to maximize their use of RN for the environment they are in. If the climate changes in that area the plant would not be able to survive.