4.11 Italy
For Italy a number of flood-related maps have been made available. However, no information has been provided
on the mapping programme, mapping authorities or any other background information.
Figure 4.68
Flood extension and risk map in Italy (location Rieti)
On the flood extension map (Figure 4.68) both the flood extension is shown (for 3 return periods: 1/50, 1/200
and 1/500 yr) and three levels of risk (R2, R3 and R4). This risk factor R is defined on the basis of two parameters:
sensitivity and probability. One of these two factors (probability) is already shown on the same map (inverse of the
return period) and the risk factor is obtained by overlying this information with land use and urban planning. The
latter is remarkable, because it implies that future urban layout is taken into account. In total there are four levels
of risk (R1 – R4). Risk area R1 is characterized by a low sensitivity, because its specific use implies a low probability
of human loss or because it falls within areas characterized by high return periods. The level of risk increases from
R4 to R2:
• R4: Return period of 1/50 yr and high level of sensitivity
• R3: Return period of 1/50 – 1/200 yr and high level of sensitivity
• R2: Return period of 1/200 – 1/500 yr and high level of sensitivity
The process of derivation of risk areas is shown in Figure 4.69 - Figure 4.71 for the river Tevere with a total
population of about 4.3 million persons. The Tevere river passes through the city of Rome towards the
Mediterranean Sea and as such is a very relevant example of flood mapping in an urban area.
On Figure 4.69 the vulnerability / sensitivity is indicated of exposed assets (i.e. types of buildings, sport facilities,
waste dumping areas, power plants, etc.). In the vulnerability maps, red indicates the most vulnerable locations,
which is logical. However, green indicating the least vulnerable locations might suggest that these areas are safe,
which is misleading.
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Atlas of Flood Maps
On Figure 4.70 the flood extension for the three return periods is shown. Use is made of colours that are normally
associated with a danger level, e.g. red is used for the flood with the highest probability (1/50 years) that can be
expected to have the highest water depths and flow velocities.
On Figure 4.71 the combination of the two former maps into a flood hazard map is shown. Use is made of the
colour red again for the highest flood hazard.
Figure 4.69
Vulnerability of exposed assets in the river valley of the Tevere
Figure 4.70
Flood extension map for 3 return periods (1/50, 1/200 and 1/ 500 years)
Atlas of Flood Maps
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Figure 4.71
Hazard map (combination of vulnerability and flood extension maps) for 3 return periods
Comments on the maps
The maps for Italy give one of the scarce examples of flood risk maps (probability versus consequences). The
method is easy to understand, but the use of the same colour (e.g. red) for high vulnerability and high probability
might cause some confusion.
In addition, the use of green for areas of low probability c.q. vulnerability may lead to the misleading conclusion
that those areas are safe, while this is not the case.
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Atlas of Flood Maps