Impacts and Risks of Global Change - Impact of Global Changes on Mountains: Responses and Adaptation - page 59

Both vulnerability and resilience have a dynamic character, as they are
subject to temporal and spatial changes within the relationships between
forcing and reacting systems (see Bohle and Glade 2008), thus being key
pre-requisites for the understanding of human-environment systems in
their attempt to adapt.
Risks related to natural hazards
In Central Europe in general and in the Alps in particular, a surprising
clustering of extreme runoff events with a recurrence probability of one in
100 years and less is evidence that the frequency-magnitude relationship
of natural hazard processes triggered by hydro-meteorological driving has
undergone a marked change (fi rst noted by Bader and Kunz 1999). The
analysis of fl oods since the 1990s shows i) runoff maxima exceeding all
measured records, and ii) the coupling of two or even three extreme fl ood
events in independent river systems within a short period of time which is
statistically highly unlikely (Stötter et al. 2009). Most prominent examples
are the fl oods of both Bregenzer Ache and Lech in the years 1999, 2002 and
2005. The statistical probability of such an accumulation of extremes of
approximately 1:30,000 highlights, how unlikely and thus how signifi cant
these events were.
These events may be seen as a clear indicator for a trend towards a more
intensive precipitation—runoff relationship as a consequence of global/
regional warming. Recent modelling of future scenarios supports the idea
that due to seasonally differentiated warming with maxima from May to
August and from November to February and marked increase of mean
precipitation in the winter season will cause new patterns of the frequency-
magnitude relationships. This new trend is additionally supported by the
fact that higher winter temperatures will cause a tremendous rise of the
snow line, which means that a much higher portion of winter precipitation
will fall as rain (see Beniston 2003).
As major consequences within in mountain human-environment
systems, this development of precipitation-runoff relationships means a
major threat to the natural hazard management system. As this is based
on the acceptance of defi ned protection limits (goals) and remaining risks,
it does only provide measures against, e.g., fl oods, which have so far been
understood as 100 years events but may now and in future be expected
to occur more frequently. The extreme socio-economic changes since the
mid 20th century, resulting in population growth and rapidly increasing
numbers of houses and other values further contribute to this new challenge.