[dentstudent (OP)]

It seems as though it is raining all over the world at the moment (with the possible exception of Australia). Floods in India, Mexico, the UK, heavy rain over Europe.

Water evaporates to form the clouds that provide the rain, but how much of a fluctuation is there in the volume of water held in the atmposphere? What percentage of the earths water is this?

[another_someone]

It seems as though it is raining all over the world at the moment (with the possible exception of Australia). Floods in India, Mexico, the UK, heavy rain over Europe.

Water evaporates to form the clouds that provide the rain, but how much of a fluctuation is there in the volume of water held in the atmposphere? What percentage of the earths water is this?

Except, I also believe, from what I have been informed, that Florida is in drought.

The first question is whether there is really a substantial shift in the amount of rainfall, or simply a shift in where this rain is falling.  My understanding is that over the last few years, the high pressure system that usually sits over Europe, had been pushing further north, and covering much of England (or at least the souther region), whereas this year it shifted further south.  To what extent did this simply mean that this year we are getting rainfall over land whereas in the past few years exactly the same precipitation was just falling into the sea, and so not being measured by anybody?

[JimBob]

It seems as though it is raining all over the world at the moment (with the possible exception of Australia). Floods in India, Mexico, the UK, heavy rain over Europe.

Water evaporates to form the clouds that provide the rain, but how much of a fluctuation is there in the volume of water held in the atmposphere? What percentage of the earths water is this?

It is dependent on the temperature and pressure. The relationship is defined by the ideal gas law

P₁*V₁ / T₁ = P₂*V₂ / T₂

where P = pressure, V = volume T = temperature

I could probably search the web and find out how much is in the atmosphere on average but I am very lazy and undependable and a totally dispicable person and will just ignore that part of the question.

I didn't see it.  []

[another_someone]

It is dependent on the temperature and pressure. The relationship is defined by the ideal gas law

P₁*V₁ / T₁ = P₂*V₂ / T₂

where P = pressure, V = volume T = temperature

I could probably search the web and find out how much is in the atmosphere on average but I am very lazy and undependable and a totally dispicable person and will just ignore that part of the question.

I didn't see it.  []

I suspect there are greater complexities than this, since one can have supersaturation and nucleation all having an impact on the water content of the atmosphere.  Plus, one has to take into account the different between actual water vapour, and suspended water droplets (or ice crystals suspended in air).  Clouds are not water vapour (since water vapour is transparent), but water condensate held aloft.  This is a key distinction, because water vapour is a potent greenhouse gas, while suspended water condensate will cool the Earth by reflecting sunlight back out into space.

[paul.fr]

This is worth a few minutes of your time
http://www.st-andrews.ac.uk/~dib2/climate/water.html

...Water vapour
Water vapour (the gaseous form of water) can exist in the atmosphere as part of the mix of atmospheric gases.
Q: How much vapour can there be in a mass of air?

A: A useful measure of the amount of water vapour in the air is the mixing ratio, r:

r = mv/md

(mv = mass of vapour; md = mass of dry air).

...

[Andrew K Fletcher]

Well it's raining here and has been for quite a few days now. I have placed a bucket outside to measure how much is in the entire atmosphere. I will gladly send the water to anyone doing the math

[crandles]

On average water stays in the atmosphere for ~11 days.

Found a book from an OU course which says "If all the water in the atmosphere fell evenly as rain around the world, the rainfall would be about 30mm deep."

Global mean annual precipitation is about 1000mm. Those figures seem consistent.

I therefore suspect with only 11 days in atmosphere the variation is not that great globally but the smaller an area you look at the greater the variation.

Not sure about volume of earths water but I estimate water in atmosphere is less than 0.1% of the worlds ice and probably nearer 0.05%.