Climate Change and the Water Cycle - Some Information Concerning Precipitation Trends

Abstract

Water in sufficient quantity and acceptable quality is of vital importance for all life on Earth. Unfortunately, these conditions are not fulfilled in many parts of the world, especially in the suptropical and partly also in tropical regions, so that approximately 1.2 billion of people (c. 20 % of the world population) have no secure access to clean drinking water (Lozan et. al., 2007). Moreover, agriculture suffers from water supply problems. Even in some industrialized regions of the mid-latitudes climate zone where humid conditions prevail, for instance Central Europe, dry spells can lead to serious problems. An example is the hot-dry summer 2003 (Schonwiese et al., 2004) leading to at least 35,000 additional deaths and economic loss of c. 13 billions of dollars in Europe (Jendritzky, 2006; MunichRe, 2004; Schar and Jendritzky, 2004). Another problem, in addition to too few water, is too much water as a consequence of heavy precipitation episodes leading to flooding. The question arises whether such problems may become more frequent in the future. In the following the problem of global climate change is briefly addressed (chapter 1.2.2), mainly in terms of temperature rise. Then, the consequences for atmospheric circulation and, in turn, the global water cycle are outlined. The most important component of the water cycle is precipitation playing a crucial role not only with respect to both dryness and flooding but also concerning water supply of mankind. Therefore, two chapters address the observed precipitation trends on a global scale (chapter 1.2.3) and in Europe (chapter 1.2.4). As a case study, in the context of precipitation trends observed in Germany, the problem of extreme events is discussed (chapter 1.2.5). Finally, some conclusions are added (chapter 1.2.6).