risk management - monitor ii

20 Monitor II Hazard maps
Monitor II Hazard maps 21
The theoretical return period is the inverse
of the probability that a defined intensity of
an event will be exceeded in any one year.
For example, a 100-year flood has a 1%
(1/100=0.01) chance of being exceeded in any
one year and will on average occur once every
100 years.
As regards flood return period, it should
be noticed that there are significant differences
in the adopted boundaries. They reflect
differences in national-regional legislations,
spatial planning and design codes of protective
structures.
Hazard potential
Hazard potential is derived by a heuristic
matrix-based combination of return-period and
intensity classes. This non-analytical approach
results in non-unified hazard classifications
among countries. For example in hazard assessment
for floods Austria distinguishes only high
and low hazard while Italy knows four hazard
classes. It should also be noticed that there are
discrepancies among countries regarding the
colour assigned to a specific hazard class when
used in hazard maps.
FREQUENCY CLASS AUSTRIA SLOVENIA AUSTRIA ITALY ITALY
Intensity
Slovenia (PP4) Italy (PP5) Austria (PP1)
Vulnerability
Figure 17: Examples of frequency classes for floods based on the return period
Figure 19: Examples of intensity classes for floods
(PP1) (PP4) (Hora maps) (PP5) (PP7)
High 1.5 m >1,5 m2/s >= 1,5 m >= 0,5 m >2 m
Medium 0.5 - 1.5m 0.5 - 1,5 m2/s < 1,5 m < 0,25 m 0.5-2 m
Low 11) &
(=