Naked Science Forum

Life Sciences => The Environment => Topic started by: Jan Bays on 28/02/2014 03:38:31

Title: Is rain finite?
Post by: Jan Bays on 28/02/2014 03:38:31

I have a question. Is rain finite? That is, if you pray for more rain to fall on your neighborhood, are you effectively praying that less rain will fall on another part of the earth?

Title: Re: Is rain finite?
Post by: alancalverd on 28/02/2014 07:49:40

Yes. As are all other materials. Whatever material thing you pray for, is an attempt to deny others.

On the other hand there may be a greater good to be achieved by localising precipitation. Cloud seeding was used with limited success to control rainfall around and over Chernobyl.   

Title: Re: Is rain finite?
Post by: evan_au on 28/02/2014 08:21:20

The amount of water participating in Earth's hydrological cycle (http://en.wikipedia.org/wiki/Hydrological_cycle) is roughly constant (if you ignore small amounts of water that are lost to space every year - and potentially, small amounts of water that are deposited into Earth's atmosphere by comets every millenium or so).

So the amount of rain is effectively unlimited, as long as there is a source of heat from the Sun to melt snow and evaporate water from oceans, lakes and trees - and cooler temperatures at high altitude, at night, or in polar regions which allow it to condense back to water again. Most water evaporates from tropical oceans, so naturally, a lot of rain falls on tropical oceans.

There is a maximum amount of moisture that can be held in a given volume of air, at a given temperature, achieving "100% humidity (http://en.wikipedia.org/wiki/Humidity)". If you live a long way from the ocean, air saturated with moisture can shed that moisture in just one place, in another place, parts in both places - or just carry it back out to sea.

Over land, a lot of rain falls on the side of mountains facing the sea; as air gets pushed up the side of mountains, it cools down, the air can hold less water and so this is often an area of higher rainfall.

If the average temperature of the atmosphere and oceans rises (eg due to climate change), there will be more evaporation, more water held in the air, and probably more violent thunderstorms and tornadoes, producing more floods in multiple places.

So be careful what you pray for...

Title: Re: Is rain finite?
Post by: CliffordK on 28/02/2014 08:28:03

The question is whether you have a fixed X amount of rain that either falls at point A or point B on the globe. 

To some extent that would be true, especially at the center of a continent.  However, a portion of the rain evaporates.  So, if rain falls at point A, some of it may evaporate and fall further inland at point B.  Certainly in the midwest USA, the humidity spikes after it rains in the summer.

Along the coast, however, it may be more complicated.  You might think of the ocean as almost an infinite source of new "rain".  Some of the rain will fall on the ocean, some will fall inland.  You won't be denying anybody rain if less falls on the ocean and more falls inland. 

I'm not quite sure the dynamics of a storm, but it may keep more rain aloft as it moves inland.  Certainly if a storm drops a foot of rain on one community, it doesn't necessarily deny other communities that rain.  In fact, a hurricane often has significant impacts across half the USA after it makes landfall.

I tend to roll my eyes a bit when people complain about a few sunny days mid-winter here.  It is quite possible that other areas could benefit from some of our winter rainfall without significant harm.  How much of our winter rain just ends up running down the rivers back to the ocean?

Here they intentionally drain down all the reservoirs during the winter to avoid flooding, whereas it can take years just to fill up Lake Mead in Nevada.

Title: Re: Is rain finite?
Post by: Jan Bays on 02/03/2014 03:49:56

Thank you all for your answers. Very helpful and clear.

Title: Re: Is rain finite?
Post by: CliffordK on 04/03/2014 06:36:21

In a sense, rain is Earth's method of sweating, so the more it rains, the cooler the planet.

Evaporation of water at the surface, and condensation in the upper atmosphere is an important transport method to move heat away from the surface.  Clouds are complex in that they shade the planet during the day, but insulate at night. 

Anyway, more rain may well mean a cooler planet.

Title: Re: Is rain finite?
Post by: cheryl j on 08/03/2014 00:12:12

So on planets that were thought to have possibly had water at one time, where did it go?

Title: Re: Is rain finite?
Post by: yor_on on 14/04/2014 01:43:24

home?

(couldn't help myself there. Too much 'life, the universe and all' as young.)

The water evaporated into space as I understands it. We also presume it to have come from space, one way or another. Maybe there exist some other explanation for it? Ah, ok, it may have gone down too :) http://www.dailygalaxy.com/my_weblog/2011/08/-mars-vanished-water-atmosphere-where-did-it-go.html
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Ok sorry, ionize is not the same as evaporate. I know, but I was lazy back then, when I wrote that. I'm much more alert now, I'm sure?