During the 20^th century, worldwide temperatures have increased by 0.7°C. The 1990's was the warmest decade but temperatures should become even higher during the first decade of the 21^st Century: 5 among the 6 warmest years were measured between 2001 and 2005. In Switzerland, temperature trends are stronger than on a global scale: an increase of 1.3 to 1.7°C was recorded during the 20^th century on the northern side of the Alps, 1.0°C on the southern side respectively. Climate models expect increasing strong precipitation events, in Switzerland as well as worldwide along with an increasing variability of precipitation, in general. This means that stronger precipitation as well as more drought events must be expected in the future. In Switzerland, an increase in the frequency of drought episodes can already be noticed on the southern side of the Alps.