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Grant
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| Present sea level is an evaporation equilibrium point ie there is no water evaporation taking place over the sea (except temporarily and locally where the equilibrium is upset) |
To this particular pig, this is not obviously true. If I leave a glass of water in my porch, it will evaporate.
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Mick Harper
Site Admin
In: London
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Let us ignore the silly bollocks from areas of the world where measurement is just not possible (eg the Sud alone extracts way more than half the Nile) and look at our own dear Thames, since that is is a situation we can be certain of.
All the rain that falls in the whole of the Thames Valley either gets transpired by plants back into the atmosphere or flows over the weir at Teddington (ignoring Ring Mains, Lea valley etc). The latter is rather less than ten per cent of the whole.
However this is the modern embanked, streamlined Thames. The natural Thames flows past Teddington and then gets mostly lost in the swamps and stews of the Thames estuary. So let us assume that, in natural circumstances, about five per cent of rainfall actually reaches the sea. Let us take that as the world figure.
All agreed?
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Mick Harper
Site Admin
In: London
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| To this particular pig, this is not obviously true. If I leave a glass of water in my porch, it will evaporate. |
Since a) your porch is way above sea level and b) the glass of water is way smaller than the atmosphere and c) has a still surface and d) is fresh and e) actually doesn't evaporate nearly as much as you actually think it does (try it!), and f) g) and a few othe things that perhaps you can assist with, your point is of limited interest.
However, if you think that evaporation is occurring as a matter of course over the ocean, then it must be occurring everywhere non-stop, so why hasn't the atmosphere reached saturation by now, after n thousand million years with water vapour at its maximum level? You will have to produce a non-satiation cycle to sustain your case.
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Chad
In: Ramsbottom
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| Mick Harper wrote: | So let us assume that, in natural circumstances, about five per cent of rainfall actually reaches the sea. Let us take that as the world figure.
All agreed? |
Nah, sorry Mick... this doesn't stack up. I estimate (and I'm pretty good at that sort of thing) using readily available data from a variety of sources, that at least 25% (and probably a lot more) of the Amazon's annual rainfall ends up in the sea... and I think the Amazon has a far larger influence than the Thames.
The situation is even worse. Take a look at this graph:
It shows that more rain actually falls over the oceans than over dry land.
All together (and being very conservative) I reckon at the very least 70% of global rainfall ends up in the sea.
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Chad
In: Ramsbottom
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The Thames situation is a little misleading.
Not all of the rain that falls in the Thames catchment area and ends up in the sea does so via the river Thames itself. There is substantial underground drainage into adjacent river basins, especially in the chalky areas of Wiltshire and Hampshire where much of the rain actually falls. This also ends up in the sea but isn't clocked up at Teddington.
If I get the chance I will try to work out some accurate figures for the Thames basin... but my guess is it will be nearer twenty per cent than five.
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Mick Harper
Site Admin
In: London
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| There is substantial underground drainage into adjacent river basins, especially in the chalky areas of Wiltshire and Hampshire where much of the rain actually falls. |
And vice versa. I am perfectly happy to accept any figure that demonstrates the orthodox picture of the Hydrological Cycle to be wrong (this, you will remember, puts plant respiration as a little side-eddy off the main torrent). Here is the 'picture' that all Earth Scientists (and all educated persons) carry around with them.
http://en.wikipedia.org/wiki/Water_cycle
In this business you have to start distrusting all 'evidence' that is acquired in support of the orthodox model. The real way to look at it is more impressionistically. Picture every bit of rainfall falling in the eastern half of Africa and then sit beside the Great Pyramid and watch how much of it actually gets to the sea. I'd put it at one per cent tops.
But as I say, so long as you are prepared to acknowledge that transpiration is more important than evaporation, we can proceed. If it will help, we shall show later that water is taken up from the sea in reasonably vast quantities by methods other than evaporation.
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Chad
In: Ramsbottom
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Providing we can lump in the evaporation that takes place from the surface of the land and its plants (as opposed to evaporation from the sea) along with transpiration, then I for one am happy to proceed.
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Chad
In: Ramsbottom
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| Mick Harper wrote: | | Picture every bit of rainfall falling in the eastern half of Africa and then sit beside the Great Pyramid and watch how much of it actually gets to the sea. I'd put it at one per cent tops. |
Pretty bloody close Mick!
The Nile Basins take up about 10% of the African landmass. They collect annually about 2,000,000,000,000 cubic metres of rain and the Nile discharges about 100,000,000,000 cubic metres per annum
In other words ninety five percent fails to reach the sea.
P.S. The above figures are calculated from a variety of reliable scientific source data.
My earlier statement...
| The Nile incidentally, manages to deliver about 50% of its contents into the Med... the other 50% being lost to evaporation on its journey through the desert and swamps of Africa |
...was taken casually from the internet. (But may still be correct... most of the rain may not reach the river(s) in the first place.)
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Mick Harper
Site Admin
In: London
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Vair well. Now that we have sowed doubt as to where the water comes from let us examine whether the claimed mechanism for water delivery actually works. Basically, the orthodox hydrological cycle requires that water is evaporated from the sea surface by the atmosphere everywhere and then deposits it on land (for the Hydrological Cycle bit of the proceedings) when the atmosphere gets, for whatever reason, colder and can therefore no longer hold as much water.
So let us use our accustomed AE technique of finding the most favourable possible example of this process and see what happens. Since the atmosphere tends to move from west to east (because of the turning earth) we need the longest stretch of west-east ocean in order to maximise overall water vapour pick-up. This is the Pacific Ocean roughly between Australia and South America.
Next, we need the quickest and least avoidable bit of the earth's surface that induces atmospheres to cool down. This is the north-south Andes mountain range which drives the air up some twenty thousand feet. So we can put these two together and, by examining the precipitation rates for the western slopes of the Andes, we can safely predict, qua orthodoxy, that these will be more or less the wettest places on earth.
They turn out to be the driest (apart from bits of Antarctica). Many of these areas have never had any recorded precipitation whatsoever. You are invited to comment on this situation. In your answer you should mention the one thing (and the only thing) that all the world's deserts have in common.
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Chad
In: Ramsbottom
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| Mick Harper wrote: | | Since the atmosphere tends to move from west to east (because of the turning earth)... |
But if you look at this map showing global prevailing wind directions, you will see that none of the deserts have a west-east prevailing wind. Eddy currents seem to override axial spin.
In fact all the deserts have either a 'land to sea' prevailing wind or an eddy current directly to the west of them.
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Mick Harper
Site Admin
In: London
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Try to keep to absolutes, Chad, you'll find that way you can finesse orthodoxy. That is why we shall be sticking to deserts for the forseeable future. Would you say that at some time in the last few centuries, a zephyr of wind has managed to cross the Pacific and reached one of those spots in the Atacama with no recorded rainfall. And if so why did it not shed any water?
PS Your claim about the wind currents and deserts is not justified by your diagram. Think of something else.
PPS Is there anybody else out there, apart from Chad, who is not keeping up or otherwise has some excuse for not taking part?
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Chad
In: Ramsbottom
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| Your claim about the wind currents and deserts is not justified by your diagram. |
Sorry, but I can't see any deserts with a west-east prevailing wind. They all have either a 'land to sea' prevailing wind or an eddy just to the west of them.
In fact the only thing all the deserts have in common (apart from a lack of rain) is the absence of a prevailing wind that has just passed over the ocean.
| Would you say that at some time in the last few centuries, a zephyr of wind has managed to cross the Pacific and reached one of those spots in the Atacama with no recorded rainfall. And if so why did it not shed any water? |
I'm quite certain the occasional zephyr does arrive (and deposits a little rain) but... "let us ignore the silly bollocks from areas of the world where measurement is just not possible"-- there is never anybody around with a measuring jug when you need one.
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Hatty
Site Admin
In: Berkshire
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| In fact the only thing all the deserts have in common (apart from a lack of rain) is the absence of a prevailing wind that has just passed over the ocean. |
The Sahara is desert and right on the Atlantic. By rights Israel should be a fertile strip of land unless you don't count the Med as sea. Plenty of wind and, like all Mediterranean countries, wettish in winter. The north is as green and wooded as anywhere in Mittel Europe and further inland the Galilee is as productive as Kent. The coast however is barren and culminates in desert proper, the Negev.
Lack of rainfall is a problem in areas that aren't officially deserts. Deserts are characterised by an absence of soil and therefore an absence of plants though there must be underground water lurking hence oases.
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Grant
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| PPS Is there anybody else out there, apart from Chad, who is not keeping up or otherwise has some excuse for not taking part? |
My head hurts.
The logical explanation for Chad's diagram is that the blue arrows tend to dump their precipitation and then the air eddies back to the equator. By the time it reaches the Sahara, or the Atacama, or whatever desert, it's dumped its water and there is none left.
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Chad
In: Ramsbottom
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| Grant wrote: | | My head hurts. |
Get plenty of aspirin ready... I feel this may be a rather bumpy ride!
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