The climatic characteristics of extreme precipitations for short-term intervals in the watershed of Lake Maggiore

Alpine and Mediterranean areas are undergoing a
profound change in the typology and distribution of rainfall.
In particular, there has been an increase in consecutive nonrainy
days, and an escalation of extreme rainy events. The
climatic characteristic of extreme precipitations over shortterm
intervals is an object of study in the watershed of Lake
Maggiore, the second largest freshwater basin in Italy (located
in the north-west of the country) and an important resource for
tourism, fishing and commercial flower growing. The historical
extreme rainfall series with high-resolution from 5 to
45 min and above: 1, 2, 3, 6, 12 and 24 h collected at different
gauges located at representative sites in the watershed of Lake
Maggiore, have been computed to perform regional frequency
analysis of annual maxima precipitation based on the Lmoments
approach, and to produce growth curves for different
return-period rainfall events. Because of different rainfallgenerating
mechanisms in the watershed of Lake Maggiore
such as elevation, no single parent distribution could be found
for the entire study area. This paper concerns an investigation
designed to give a first view of the temporal change and
evolution of annual maxima precipitation, focusing particularly
on both heavy and extreme events recorded at time
intervals ranging from few minutes to 24 h and also to create
and develop an extreme storm precipitation database, starting
from historical sub-daily precipitation series distributed over
the territory. There have been two-part changes in extreme
rainfall events occurrence in the last 23 years from 1987 to
2009. Little change is observed in 720 min and 24-
h precipitations, but the change seen in 5, 10, 15, 20, 30, 45,
60, 120, 180 and 360 min events is significant. In fact, during
the 2000s, growth curves have flattened and annual maxima
have decreased.