Arapiles says:
"Rain collection = surface area perpendicular to the direction of rainfall x rainfall"

Rain falling vertically won't be perpendicular to a pitched roof.

Exactly, which is why the pitch of the roof (and therefore it's area for a given footprint) doesn't affect the amount of rain collected.

Here's the sketch again:

.

Now do you see why you'll get the same rain collection for a given house whether the roof is steep pitch/big area or low pitch/less area?

Edited by tallbloke on 11/07/2010 04:58:21 MST.

Rog

This issue seems to be bit of an internet chicken and egg thing, with some people arguing as you are and others arguing like me - there doesn't seem to be any testing or research to support either view. Our new pavillion has a skillion roof, pitched at 10 degrees - pity I can't separately measure the water coming off that and the old part of the house with its steeply gabled roof.

Either way I have 20,000 litres of water in my tanks.

Hmmm ....

UK planning rules for rainwater runoff:

http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADH_2002.pdf

"the flow into a gutter depends on the area of surface being drained and whether the surface is flat or pitched (and, if it is pitched, the angle of the pitch).

flat roof ... plan area of relevant portion
pitched roof at 45 degrees ... plan area of portion x 1.50"

Whether the greater productivity of a pitched roof is because of more efficiency (because water runs off rather than pools) or because of greater surface area, my original contention that the pitch of my roof balances out/negates any general efficiency losses would appear to be correct.

The UK planning document lays down the carrying capacity for guttering which is designed to cope with the maximum runoff a roof will produce. On occasions when the rain is wind driven at an angle perpendicular to the pitch of the roof, there will indeed be more collection due to the greater area of a steeply pitched roof over a shallower pitched roof for a given footprint size of building.

This should not be confused with the average runoff produced. However, I will happily concede that a steep roof with an equivalent pitch on the other side of the roof will on average collect a bit more than a flat roof, because rain often is accompanied by wind, and the larger area of the steeply pitched roof facing the slanted rain will have a bigger collection area than half a flat roof. The air pressure drop over the roof ridge will cause the rain to fall more vertically onto the other side.

So I think we got to a point of agreement in the end for double pitched if not single pitched roofs.

Edited by tallbloke on 11/07/2010 06:38:38 MST.

This issue seems to be bit of an internet chicken and egg thing, with some people arguing as you are and others arguing like me - there doesn't seem to be any testing or research to support either view. Our new pavillion has a skillion roof, pitched at 10 degrees - pity I can't separately measure the water coming off that and the old part of the house with its steeply gabled roof.

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The volume of rain falling in a specified area is the same no matter what the slope of the roof it falls on. You cannot Will it or Wish it to be different.

Aristotle's Law of Identity, A = A. Not science, but logic; which is the basis for philosophy... which almost everyone hates that I discuss.

Oh, of course some will say logic is a science... But science is derived from logic, as should be philosophy.

Now that I am pointing to history (Aristotle), logic, and philosophy, we are probably entering Rog's arena of expertise.

Flame on...

:)

Nick, my engineering qualifications are more than enough to handle this particular section of discussion, but thanks anyway. :-)

On a philosophical note regarding the main topic, I'd be interested in discussing the logic of government forcing an agenda of reduction in energy production (and therefore wealth generation) on the basis of highly uncertain conjectures about the future of the global climate.

You guys are not taking into account the element of time. Water runs down faster on a more steeply pitched roof, therefore in a given amount of time more water accumulates.

Ah, thanks Miguel, that's where I went wrong.

Lol.

Logically speaking relevant to capture of rain water...

A small to large volume roof

Angled steeply or not

Being rained on lightly or heavily

ALL are at the mercy of the gutter or channel that collects the water

AND to the point where the 'cup' runneth over

RAIN - mandatory for collecting water from rain


CAPACITY
a) tank capacity - tank is very helpful, but you could just look up and open your mouth
b) gutter/channel capacity - again, very helpful for efficiency, but an open tank will collect rain ater

COLLECTOR
c) roof/collector - optional (see b)
d) if roof/collector, degree of slope - the steeper, the faster the flow
e) if roof/collector, volume - the larger, the more collection

Nature

There is rain.

capacity
Oceans/seas/lakes/etc are the tanks*
Rivers/streams/etc are the channels

Collectors
Mountains are the steep roofs...plains are the flat roofs

*and ice caps are long term storage or short depending on your carbonflamery

There have been some interesting studies done correlating solar activity levels and the flooding of the Nile. Also the flow in one of the big south American river systems, the Parana.

I made an interesting discovery which I'm trying to get the climate scientists interested in. The level of specific humidity up at the top of the troposphere (our atmosphere below the stratosphere, about 30,000 feet) correlates with solar activity too.

.

Unfortunately, they are so stuck in their co2 driven climate dogma they won't discuss it with me. :-(

"On a philosophical note regarding the main topic, I'd be interested in discussing the logic of government forcing an agenda of reduction in energy production (and therefore wealth generation) on the basis of highly uncertain conjectures about the future of the global climate."

I don't think this is a question unique to climate policy. As it pertains to climate, I don't think any government is advocating reduction in energy production at the expense of wealth, they are merely encouraging/funding exploration of alternative energy production. I for one think this is a good thing! Aside from that, all governments must use a crystal ball to some extent when implementing any policies, whether energy related, health, defense, economic, environmental, etc...of course, if you disagree with their predictions and subsequent policies (and live in a theoretical democracy) you can choose not to vote for them next time around, or lobby them in this term to change their policies.

As for rainfall, there is no doubt that x-amount of rain will fall over x-amount of horizontal area, no matter what the slope of the roof (assuming no wind). I can't believe it's even a matter for discussion, though as Rog generously admitted, and I concur, wind can have an effect of a probably very small amount.

Lynn, one of the worlds foremost climate scientists Judith Curry, is making an effort to build bridges of open debate between the AGW advocates and the sceptics.

http://judithcurry.com

Her CV

http://curry.eas.gatech.edu/currycv.html

She has been forthright and highly critical of the core team of IPCC scientists for their dogmatic attitude and dubious data practices. It will be interesting to see how it pans out, though so far the scientists seem reluctant to engage. Not surprising since they don't have a leg to stand on...

On a philosophical note regarding the main topic, I'd be interested in discussing the logic of government forcing an agenda of reduction in energy production (and therefore wealth generation) on the basis of highly uncertain conjectures about the future of the global climate.

------------------------------------------------------------

Start Here:

http://blogs.news.com.au/heraldsun/andrewbolt/index.php/heraldsun/comments/column_why_you_may_soon_need_a_warmists_permission_to_eat/

Edit: couldn't get the HTML link to work. Sorry.

Edited by ngatel on 11/08/2010 21:48:00 MST.

Absolutely ridiculous.

Going after tall people would be a could idea, too.

And middle aged men that are not bald should have to pay dearly for their hairprint!

Absolutely ridiculous indeed...especially if anyone is seriously worrying about this. I'm just surprised the plan didn't include black helicopters, the United Nations, and an army of Obamatons to kick your door down.

"Start here"

Or here;
http://scienceandpublicpolicy.org/images/stories/papers/originals/western_climate_establishment_corrupt.pdf

An Australian climate scientist who is now retired from the Greenhouse tells a few home truths in an easily digestible format.

good on yer!

Tonight (11/9/2010) was listening to PRI while driving home from some out of town work. By chance I caught a lively debate about global warming. Dessler, Taylor, Vidal, others. Taylor really held his ground IMO.

I'm trying to find a recording of it on Web, but so far no luck.

Hearthland posted an article already about Dessler's comments about US CO2 emissions.

Rog,

Nice link! Pictures alone convey a great deal.