Population density and climate

Something that struck me quite some time ago as an eyeball-quality correlation was that population density was higher in areas with more rainfall. A proper study of this should look through history and be rigorous about both quantities. As long distance large-scale trade of food became possible, it'll also be necessary to look at water requirement for food and for people separately.

But, as a start and something of a Fermi estimate, let's go with what my water company tells me is typical per-person water usage at home -- 70 gallons per day. That's approximately 250 liters. Typical annual rainfall around here is about 1 meter per year. So, if I captured all the rain that fell on an area, how large would that area have to be for me? If everyone else did the same, how many of us could live in 1 square km?

The 250 liters are what I'd use in 1 day if I were approximately 'average'. For a year, I need 365 times that much, for about 100,000 liters. 1 liter is a cube 0.1 m on a side, so for a year's water I need about 100 m^3. That'd fill 1 meter deep across a square 10 meters by 10 meters. Since I get about 1 meter rain per year, this says I need about 100 square meters. If we all caught absolutely all rain, and didn't lose any to trees, farming, industry, grass, ... this would let us go up to a population density of 10,000 per square km (about 25,000 per square mile). This is actually something like the density of the highest density large cities -- check out Chicago, New York, London, Paris, for instance.

Los Angeles gets about 0.4 m/year rain, and Phoenix about 0.2. Their densities are about 3200 and 1200, respectively (Wikipedia for both numbers) to the 4000 and 2000 we'd guess from the above. On the other hand, both illustrate the fact that cities don't rely on only the rain that falls on them. Both have extensive systems to bring water to them. This is not new; Rome, to support its population in the days of Empire, when they were also using 10s of gallons of water per day, built a tremendous system of aqueducts to bring water to the city. New York and Chicago, I know, also bring water from outside the city (again water systems, rivers, lakes).

If we figure on about 10% of the rainfall being captured for residential use, then we're down to about 1000 per square km, or about 2500 per square mile in my part of the country. These are densities comparable to what is seen over moderately large areas (entire metropolitan regions, small countries in northern and western Europe, ...) with meter per year rainfall.

There's a certain reasonability, then, to there being a relation between rainfall and population density. You can exceed that relation, but only at the expense of building a large scale water system -- and not letting people in the areas you bring water from have acess to it. Water rights have a lengthy and often not peaceful history. In any case, even if all the people are in one place, their requirement extends over a larger area, something more in accord with the 1000 per square km (for 1 m/year rainfall). For, say, the 20 million or so people in the Los Angeles area, with 0.4 m/year of rain, it says their footprint is more like 50,000 km^2, to the 4000 or so the metro area actually occupies. These are all still Fermi estimates, of course. It does point out to us, however, that urban areas likely have a footprint rather larger than the official area. Conversely, it means that they need to be concerned about weather and climate over a larger area than just their own borders.

The climate concern is ... what do you do if you get less rain (or less snow)? What do you do if the rain comes more in situations (thunderstorms) that are harder for you to capture the rainwater from? Either of these changes drives you to a lower population in your urban (including suburbs) area, or pins a new expense on you -- to build more extensive water systems, and systems able to handle greater rainfall rates. While we mostly expect rainfall to increase, we do expect that there will be areas which will see falls. Which ones, not so sure, but some. It's expected and observed that there'll be an increase in rain falling in heavy doses even where there's little change in total rainfall.

A friend mentioned a TV person-in-the-street interview during a local drought. The person wasn't concerned about the drought and low river levels because "I don't get my water from the river, I get it from the tap." I trust you all know that it went from the river through a processing system to her tap even if she didn't. (Or, in the case of Chicago, from Lake Michigan -- whose level seems to be falling more than the usual cycle.)

It seems more people don't realize that wells have the same problem. Across much of the Great Plains US (take Kansas for a central example state), farming and residences take advantage of the Ogallala Aquifer. The problem is, aquifers need recharging. That is, the water in the aquifer comes from rainfall elsewhere. With the Ogallala today, the usage exceeds the recharge rate. This is not very surprising, as the aquifer's recharge area is itself in fairly dry areas. For more, see the USGS web site, search on Ogallala Aquifer and recharge. Similar problems exist for many wells. The main difference between wells and lakes or rivers is that you can't see the levels dropping as easily.

Science fiction and science

Many scientists are (or were) science fiction readers, and I'm no exception. Some questions are currently making rounds for the ScienceOnline '09 meeting, from http://almostdiamonds.blogspot.com/2008/11/science-and-fiction-open-call.html
and I'll take a shot at them myself:

1. What is your relationship to science fiction? Do you read it? Watch it? What/who do you like and why?
2. What do you see as science fiction's role in promoting science, if any? Can it do more than make people excited about science? Can it harm the cause of science?
3. Have you used science fiction as a starting point to talk about science? Is it easier to talk about people doing it right or getting it wrong?
4. Are there any specific science or science fiction blogs you would recommend to interested readers or writers?

1) I used to read a ton of it, and now merely moderate amounts. I watch some, but it's mostly movies rather than television since we ditched our cable. In term's of what I like, I'm minded of the comment that "The Golden Age of science fiction is 13" -- whatever you were reading at 13, that's what you like best. I happened to be reading even older SF than what was contemporary to my age 13, so I'm biased towards 40s to mid 60s SF. Among more recent authors, which says something about my reading curve as well, I like Cherryh, Bujold, Brin, and several others who aren't leaping to mind as 'recent'.

2) Almost all SF is actually engineering, rather than science, -oriented. Some technology is developed which has some effects on society or people and then we wonder what they're going to be. Or some part of the universe (aliens, black holes, ...) drops in on our characters and we wonder how they're going to stay alive .... And so on. I don't see this in a conflict with science, and, in fact, supports well what I think are some very important attitudes for doing science or living in a society where science is important:

• The universe is a very interesting place (so study it)
• Understanding more about the universe can keep you alive
• Science translated to technology can affect how you live (so think about the social effects sooner rather than later)
• Problems are (generally) solvable, the universe is (often) understandable

Bad SF, I suppose, can fuel some bad ideas about science (_all_ problems can be solved, typically in 30-120 minutes of viewing; science is really just another word for magic), but that sort of thinking is fueled much more by the non-SF parts of society than the SF, even bad SF.

3) I don't use SF specifically; perhaps I'd do so more if I were teaching more. But I do take advantage of a somewhat SFnal view of the universe in doing my research. That is, I'm trying to understand, say, the earth's climate. That's only one place with one particular set of conditions. What (the SF-fan in me asks) would it be like if the earth rotated much faster, more slowly, if the sun produced less UV (hence less ozone on earth, hence less greenhouse effect in the stratosphere, hence ...?), if the earth were farther away/closer in, and so on. I can't say that it's resulted in any journal articles that I wouldn't have written anyhow, but it does make it easier for me to, say, read paleoclimate papers (the earth did rotate faster in the past, sea level has been much higher and lower than present, ...)

4) As to recommendations ... I suppose the main one would be something that SF (that I saw) didn't predict we'd be taking advantage of: Read a bunch of them, and written from different viewpoints including those which disagree strongly with your own.

Fermi estimate challenge

I'll invite you to help me with this challenge, namely by providing the challenges. Enrico Fermi was famous for being able to estimate physical quantities even in situations where he did not (and, possibly, nobody) knew what the actual answer was. This is enormously helpful in science. One of the things we need to know is whether the answer we got back from our observing system or calculation was reasonable. When you start working in brand new areas, it's much harder to know what is reasonable. A Fermi estimate gives you that first guess. As Fermi also was a Nobel Laureate and did a lot of creative, original work, it might be a good thing if we practiced this skill ourselves.

Fortunately, you don't have to be a Nobel Laureate to do it, and the subject needn't be one on the frontiers of human knowledge. I made some use of it, for instance, regarding the company 'Joe the Plumber' wanted to buy. (After doing so: it isn't a small company.) The classic example is to estimate how many piano tuners there are in New York city. But I've seen that one a bunch of times, and don't have a piano, so it lacks something for meaning. The reason I need your help is that anything that leaps to my mind to create an example from will be in some area that I know something about already. So, what number -- about the world -- would you like to see estimated? No 'guess what number I'm thinking of' or 'what is the tangent of a trillion'? But something about how many, how big, how hot, ... of something in the observable universe.

Large population countries

Partly because of my recent trip(s) to China, but also as a continuation of an idea I started in describing the ocean and atmospheres, I'll take a look at national populations today. In terms of the oceans and atmospheres, I looked at what they were composed of, and found that rather few elements were sufficient to cover a large fraction of each. It's a larger group for countries, but, still, fairly few (less than 10%) of the countries are required to cover over half the population of the world. The figures here are 2005 numbers from the 2006 Information Please almanac. They'll have changed since then, of course, but more on that later.

From a world population of about 6.6 billion, countries with more than 1% of the world's population are:

1. China, 1300 million
   
2. India, 1100
   
3. USA 295
   
4. Indonesia 242
5. Brazil 186
6. Pakistan 162
7. Bangladesh 144
8. Russia 143
9. Nigeria 128
10. Japan 127
11. Mexico 106
12. Philipines 88
13. Vietnam 84
14. Germany 82
15. Egypt 77.5
16. Ethiopia 73.1
17. Turkey 69.7
18. Iran 68.0

That's it. Of 192 members of the UN (current tally on Wikipedia) , only 18 have more than 1% of the world's population. They account for a little over 2/3rds of the world's people (68%). The first 6 account for half of all the people in the world.

One thing this suggests to me is that for modern citizenship, history, geography classes, it would be a good idea to learn some specifically about these countries. If only some bare elements of things like capitals, languages, religions, a bit of history, etc. In bygone days (i.e., when I was in elementary school), we did do that sort of thing, but only for the US plus western Europe. You'll notice up there that only 1 western European country is on the list. In other words, such an education didn't do much good towards living in the world I find myself in. Actually, my school did cover most of the rest of the list but we were distinctly odd for our time and area.

The up side of learning about this set is that, while it covers a large fraction of the world's people, the list is short.

If I drew up the comparable list for, say, 1939, you'd find far more European countries present. If I did it for 1880 or so, it would be even more Europe-heavy. I'll get to those at a later date.

A different list would show up if I did it in terms of the global economy, one much heavier on Europe. But you'd see many of the same contries on that list. 4 of the G8 are already on this listing. And a somewhat different list would show up by listing countries in terms of land area. Again, though, most of the largest are already given (in rough order, the biggest are Russia -- huge, Canada, US, China, Brazil, Australia -- all very large, India, ... 5 of the 7 are already shown above).

If anyone would like to take on constructing comparable lists -- countries with 1% or more of world GDP, countries with 1% or more of world land area, countries with 1% or more of world ocean EEZ area (Indonesia moves way up!) inside their exclusive economic zones (EEZ) -- please do send it in. I'll get there one of these days, but, as my recent posting rate suggests, this can be a while.

The European Union presents some problems for such list-making. The current EU-27 represents about 500 million people, so would be number 3 on the above list (and take Germany off it), and be a 'country' larger than India in land area. On the other hand it isn't exactly a country. I just finished reading Postwar: A history of Europe from 1945 to the Present by Tony Judt. 'What is Europe' is a more interesting question than I'd thought.

Back again

Back from China ok, aside from a cold. The trip was good, my first time in an Official Delegation situation. I believe I managed ok, using my chopsticks reasonably and toasting appropriately, if on the lighter end. (Fortunately, my counterparts were also on the lighter end by preference so it all worked out.)

I have some comments in queue and some going back a ways that I've meant to respond to. As my eyes quit watering, etc., I'll be getting back up to speed.

Off to China

It'll be even quieter here for the next week or so. I'm travelling to China for the World Ocean Week. As I've mentioned, science is international. That includes going places to talk to people. If all goes well, we'll find some interesting areas for collaboration to improve both countries' ocean work.

Election Day

US readers, please do get out and vote. If you have to endure some rain, well, you're not water soluble.

Happy 30th to sea ice

A belated happy 30th birthday to our continuous* record of sea ice coverage from satellite! 26 October 1978 is the first data from the SMMR instrument, so last weekend the record finally hit 30 years.

* Ok, not exactly continuous, there's a gap between SMMR and the first SSMI to follow. But it's only a matter of (quite a few) weeks, rather than years as happened between ESMR and SMMR.