Urban environment

In 1950 the world population was about 2.500 million people. Now, 65 years later, the world population has reached about 7.200 million people (see the diagram below, the black curve). 

Humans mostly live in houses and use paved roads to move to other people and other places. Therefore, it is easy to understand that the grow of the world population by 4.700 million people during the last 65 years had consequences to the arrangement of the surface area of the continents of the planet. The natural cover of the land by grass, plants, bushes and trees is further decreased and is substituted by man-made houses, buildings and roads. Moreover, to feed all those people is impossible without a large increase of the area of cultivated farmland.

In 2012 the ARLEM published an alarming report about the desertification and climate change in the Mediterranean. At first sight, there is no connection between the desertification of  the countries around the Mediterranean Sea and the climate in modern West European cities, like the city of Amersfoort. Unfortunately, there is.

The desertification of natural ecosystems is a long lasting degradation of the original flora and fauna of an area. The degradation of an ecosystem into a dessert is mostly a result of a combination of factors. Nevertheless, from the climate point of view the final result is the same.

The climate in the area will change because the temperature raises during daytime for at least half the year and the aridity increases too. There is a lack of rain and periods of long droughts become regular. The image below shows the desserts and the vulnerable areas on the world map (click to enlarge).  The revolving globe in Google earth shows the situation in a more realistic way.

The expansion of modern cities during the last 65 years by the grow of the world population has some effects that can be compared to the desertification of land.

The surface area of a modern city is predominantly made of stone, concrete, asphalt, paving stones and gravel. The natural cooling of the air by the evaporation of water by plants and trees during solar radiation – caused by the process of photosynthesis is largely disappeared. Moreover, all the rainfall upon the roofs of houses, buildings, pavements and roads is drained to surface water. The consequence is a decrease of the absorption of water by the uncovered ground.  

The image below shows the temperature of the surface areas of the city of Atlanta, Georgia, USA caused by solar radiation on man-made surfaces during daytime.

The result of the concentration of man-made buildings and roads – and the arrangement of the interior of a modern city – is a raise of the temperature of the city in comparison to the surrounding rural areas. This effect is named urban heat island.

It is clear that the micro climate of the ever growing modern cities have a lot in common with the increasing desertification of land.

Next chapter: "Global warming"