The origin of the population data is described in . This data has a resolution of (about 54.7km) i. e. the earth is divided into a number of spherical rectangles of size as above and the number of inhabitants in some of them is given, and represents the human population of the earth for 1994. Note that it will be hard to use realistic population data with much better resolution, since the actual point of living of the humans is not of great interest to us. In western Europe, north America and similar regions of the earth, the location of living of a human can differ significantly from the location where the individual spends a large amount of his time. It has been estimated that the average daily activity radius for a human being living in western Europe is ca. 15km . Although the actual radius is cultural, environmental, social, and urban/rural dependent, we see no reason to use a higher spatial resolution of the population distribution pattern. No attempt has been made to extrapolate the data given to the time period in which the simulation takes place (see Section 6.1.3). While this might be an important issue in developing countries to account for migrational patterns, birth and death rates, and outdated data, it was felt that this does not compromise data accuracy here.
Since the population data used by OLAF is discretized on the meteorological grid, the original data has been bilinearly interpolated to generate the corresponding values. Figure 6.3 and 6.4 (p. , ) show the resulting discrete distribution function interpolated by bicubic splines.
In total, roughly 58 million people live in the region which the case study considers.
Figure 6.3: Population distribution on the computational grid as seen from the southwest. The highest peak represents Paris, the "hills" near the far away corner are the cities in the Rhine-Ruhr area. On the left side, greater London area is just cut off.
Figure 6.4: Population distribution on the computational grid as seen from the north east. Compare also Figure 6.3. The small peak just in front of Paris is Brussels.