General Introduction

Abstract

The world is urbanizing rapidly. In the year 1900, the total world population was around 1.6 billion people, of which 13% lived in cities (United Nations 2003; United Nations 2006). Within 105 years, the total world population increased to 6.46 billion people and the percentage of urban dwellers increased to 50% (United Nations 2006). This development is projected to continue to a total world population of 8.2 billion people and 60% of urban dwellers in 2030 (United Nations 2006; Fig. I1). In Europe and Germany, the percentage of people living in urban areas is even higher, with 72% and 75% respectively (United Nations 2006). Naturally, the increase in urban population was and still is accompanied by an increase in urban land use. In Germany, settlement and transport areas cover around 13% of the total land surface (Umweltbundesamt et al. 2007). Although this is far behind agricultural (53%) and forest land cover (30%), urban land use is the land-use type with the highest growth rate: Around 114 ha of land in Germany are transformed to settlement or transport area every day (Umweltbundesamt et al. 2007).