Die Starkregen und Massenumlagerungen des Juli-Unwetters 1987 im Tessin und Veltin

Abstract

Between July 16 and July 19, 1987 heavy and intensive rainfall with a maximum of 392 mm/d (Maggia) caused extensive rockslides and land slips as well as severe erosion and flooding in the southern Alps, and particularly in Valtelline in northern Italy. There the landslide activity was far stronger than in Tessin in southern Switzerland, although the total amount of precipitation was much higher in the latter area. The differences in the extent of damage in these regions with similar geological and tectonic conditions can be explained by application of magnitude-frequency analysis of rainfall events with a duration of 48 hours. Resulting from these analyses the recurrence interval of high intensity rainfalls in Tessin is very much shorter than in Valtelline. Newspaper coverage overemphasized the significance of environmental damages as causes for the disastrous landslides; however, they did not consider the extraordinarily high intensity of rainfall as the most effective geomorphological process event.