1 The relationship between population and water
Last week you looked at how the population of the world has increased, particularly in the twentieth century. However, population growth has not been uniform across all areas of the world. In this section you’ll learn about the relationship between rainfall and population.
The need for water to maintain human life, both for essential drinking water and cultivating food, means that human population in desert areas are generally very low. Populations are very much higher where there are plentiful supplies of water. This is evident from comparing the two maps in Figure 1.
As you will appreciate, because the Earth is a sphere, the views in Figure 1 are not those you would see if you could look down on the Earth from space. The advantage of maps like those in Figure 1 is that they allow the whole surface of the Earth to be shown in one picture. As was mentioned last week, scientists often use diagrams to represent particular aspects of an object, and these diagrams are rarely accurate representations of all aspects of the object. The population map, for example, shows the world as a flat sheet, with Alaska a long way from Siberia, whereas a look at a globe will show that they are close together.
However, as long as you bear in mind the limitations of this sort of map, it is a very useful way to convey information about the population of all regions of the world in a single diagram.
Figure 1 (a) shows how densely populated the different areas of the Earth are. The population information is conveyed by the dots on the map, and the caption tells you that each dot represents the same number of people. This means that, where the dots are very close together, more people live in that region. In other words, there is a high population density in that region. England, for example, has a high population density overall, and the dots are close together there. If you live in a rural area, you may find this concept hard to comprehend, but the low population density in the countryside is balanced by a far higher population density in cities and towns. To read Figure 1 (a) you don’t need to know how many people each dot represents. All you need to know is that the more dots there are in a given area, the more densely populated that area is. The impact is immediate.
Activity 1 Interpreting information from figures
- a.From Figure 1 (a), which are the most densely populated areas of the world? Which are the least populated?
- b.Figure 1 (b) shows how rainfall (or snowfall) varies in different regions of the world. Which are the areas with the most rainfall? Which are the areas with least rainfall?
- c.Consider the visual impact of Figure 1 (b). Do you think the colours used were chosen randomly? If not, what do think the colours in the key represent.
- d.Are there any features, such as geographical area, which are labelled in one map and not the other? Why do you think this is?
- a.According to Figure 1 (a) the most densely populated areas of the world are India, China, Japan and Europe. The dots are the closest together in these areas. The least populated areas are North Africa, Australia, parts of Russia and Siberia, Alaska and Canada, and parts of South America.
- b.The areas with the most rainfall are around the equator, particularly in South America, Africa and the islands north of Australia. The areas with the least rainfall are the Atacama Desert in South America, the Sahara and Kalahari deserts in Africa, the Arabian Desert in the Middle East, the Thar and Gobi deserts in Asia and the Australian desert.
- c.The colours have associations. Blue is traditionally the colour of the sea, a watery environment: the darker the blue, the more watery the environment. Yellow is the colour of sand, which is associated with deserts. These sorts of associations make it easy to distinguish at a glance the wet areas from the dry areas. In Figure 1 (b) there is a key to show you what the different colours on the map mean. Hot desert areas where it seldom rains are yellow, and areas where there is heavy rainfall throughout the year are dark blue.
- d.Several features have been labelled in Figure 1 (b) that were not labelled in Figure 1 (a), notably the locations of the Equator and the Arctic and Antarctic Circles. The Arctic and Antarctic Circles were not labelled on Figure 1 (a) because they were irrelevant to the discussion of the world population distribution. However, they are relevant to the consideration of world rainfall and deserts. You probably associate the Arctic Circle with cold temperatures and the Equator with hot temperatures. The closer to the Equator you are, in general, the higher the average annual temperatures and so the more likely you are to find hot deserts if there is little rain. Beyond the Arctic Circle, you are likely to experience snowfall rather than rainfall.
When you compare the maps in Figures 1 (a) and (b) you will see that areas of very low rainfall generally match up with the low population density area. There are, however, two clear exceptions that you might have noticed. These are along the Nile river valley in Egypt, and along the Indus river valley in Pakistan. The Nile and Indus valleys have desert climates with little rainfall. The large rivers that give their names to these valleys bring water from the mountains, which can be used for drinking water and crop irrigation, and so that high populations can be supported in these areas.
It is known that water is essential for humans, and therefore one conclusion to be drawn from these observations is that human populations are concentrated in regions where they have access to water. Next you’ll look at the quantities of water that are required to sustain human populations.