Dew measurement

[rmw]

How can you differentiate between dewfall and other forms of precipitation in measurements?

 

How much water is deposited, say per acre or hectare, by dew?

[CaptainPanic]

It's a tricky question.

 

The amount of dew you get is mass-transfer limited, so the larger your surface area, the more you can get.

Also, the temperature of the surface on which the dew is being deposited is critical... some surfaces cool much faster than others, and therefore will collect more dew overnight. For example, the roof of a car cools quickly, and will be dew or frost covered the next morning.

 

But, a rain gauge should get very limited dew inside of it... so, although it is not perfect, it's probably the easiest and best way to measure rain.

Then you should take a surface area on which dew deposits easily... and measure the increase on weight of that too.

 

Then you know rain for a certain area (square meter or something), and the rain+dew for another surface area. Convert to the same surface area. Subtract the first from the second, and you have only the dew.

 

It might be interesting to take two very different surface types for the dew measurements.

 

Good luck!

Edited February 21, 2011 by CaptainPanic

[John Cuthber]

A plate under a "roof" can pick up dew, but not rain.

[Mr Skeptic]

A plate under a "roof" can pick up dew, but not rain.

 

It will also give the wrong number, for the same reason that there is less dew and frost under a tree -- the dew is dependent on the temperature, and being able to "see" the cold night sky will lower the temperature.

 

How can you differentiate between dewfall and other forms of precipitation in measurements?

 

How much water is deposited, say per acre or hectare, by dew?

 

I think that you could measure the dew when it is not raining. Then, try to calculate out what you know based from the humidity, temperature, and cloud cover to extrapolate for when it is raining. I think that if any dew condenses onto rain droplets you probably have to count that as rain, unless you feel like taking rainfall readings at various altitudes and seeing if there is a difference.

 

More problems occur because to know the dew you probably have to know the total surface area and other such details of your environment (not just the "flat land" surface area like for rainfall), and because shading will affect this, and because some dew will evaporate, some might drip and some might just stay on leaves and accomplish little, ...

 

There's also precipitation of fog, which I think is slightly different than dew, and plays a major role for coastal redwoods.

 

I suppose you could measure dew with a drosometer. All hail the fountain of knowledge that is wikipedia.