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…so what’s better, an umbrella or a tree..?

They both give you shade and that’s about where the similarities end. But it is exactly that similarity that I wish to resolve, is the shade from a tree better than the shade from an umbrella?

It is reasonable to assume that one seeks shade as a respite from the sun (and the associated heat from that sun). This would then suggest that our two contestants need to not only provide shade but should also provide a drop in temperature.

As a rule, all umbrellas give good shade but they do not necessarily reduce the associated heat. Some umbrellas can actually increase this temperature marginally. They do this by trapping the air beneath the umbrella and thereby reducing any convection cooling action. One needs to ensure that the umbrella has adequate and strategically placed vents .

Trees on the other hand, come in all shapes and forms but for the purposes of this argument we will assume a tree casting a similar sized shadow to that of the umbrella. Now trees are not perfect so this shadow is going to be dappled and thus allow more sun to strike you but conversely, the tree is superbly ventilated and thus will not suffer any heat build up.

So you can be assured of cooler air under a tree than an umbrella but more shade under an umbrella than a tree! …so what’s better..?

The answer is the tree! – Our sensation of feeling cool is derived from the latent heat of evaporation of our perspiration. Evaporation is aided by direct sunlight and ventilation. The better the evaporation of our perspiration, the cooler we feel. The umbrella prevents direct sunlight AND hinders ventilation whereas the tree only limits direct sunlight AND has excellent ventilation.

– QED –

Tags: shade, tree, umbrella

This entry was posted on Tuesday, January 6th, 2009 at 3:36 pm and is filed under Nature. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.