**2. Risk assessment in land-use planning (Po basin)**

The "Operational guidelines" issued by MATTM explain the contents of EFD and highlight the difficulties in risk mapping, that is ([3], p. 20),

*"By considering the difficulties in quantifying parameters and the unavailability of reliable data of sufficient detail (…) it is reasonable to adopt, at least in this first phase, simplified methodological criteria for an assessment and representation of risk".*

and, as far as vulnerability is concerned ([3], p. 20),

The concept of flood risk in the EFD, that is,

18 Natural Hazards - Risk Assessment and Vulnerability Reduction

ing to a conceptual formula of this kind:

*with a flood event".*

*time".*

each municipality.

of relative risks.

ment plans of flood risk (PGRA).

board.

*"'flood risk' means the combination of the probability of a flood event and of the potential adverse consequences for human health, the environment, cultural heritage and economic activity associated* 

is similar to that already adopted in the PAI (Hydrogeological Asset Plan), a plan adopted by the Po Basin District Authority (PBDA [2]) in 2001, which aims at assessing and managing natural hazards and risks in the Po watershed basin (Italy). Risk was defined as ([2], p. 190).

*"expected value of the damage that the receptors can undergo on average in a predetermined period of* 

According to PAI, risk can be considered the superposition of the three elements, correspond-

R = ExVxH (1)

The aim of PAI was to express *relative* comparison of risks on the Po watershed basin, highlighting, in relative terms, the distribution of natural risks on the territory. The flood risk was not quantified in economic terms, but only qualitatively assessed with the use of indicators. The risk was determined through the use and superposition of indicators and aggregated into four classes with increasing value (1 = moderate, 4 = very high); a risk level was associated to

Therefore, the risk maps in PAI showed the different classification of municipalities in terms

The presence of PAI on the Italian territory has provided an adequate base, suitably updated, homogenized, and valued, to fulfill the obligations referred to the Article 6 of EFD. Therefore, the hazard and flood-risk maps have been obtained starting from those contained in PAI and in accordance with the "Operational guidelines" issued by the Ministry for the Environment, Land and Sea (MATTM) [3], with the contribution of ISPRA (*Superior Institute for Protection and Environmental Research)*, of the National Basin Authorities and State Regions technical

The EFD requirements about risk mapping forced public administration to find different methodologies to assess and map risk on the territory. Actually, the EFD, Article 5, forces Member state to *"identify those areas for which … potential significant flood risks exist or might be considered likely to occur,*" and risk maps have to be referred to the scale of areas at risk. Therefore, the municipality scale of PAI had to be changed according to the EFD requirements. Italian Ministry fulfilled the requirements of the flood directive, as far as the following steps are concerned: (i) preliminary assessment, (ii) hazard and flood-risk maps, and (ii) manage-

therefore implying the concept of damage and of probability of occurrence.

where E is the exposure, V is the Vulnerability, and H is the hazard.

*"Therefore, in this first phase of drawing up the risk maps, we refer to an estimate of the vulnerability … assuming an equal value (vulnerability equal to 1) in the flood prone areas; consequently exposure and potential damage (…) have been considered to be equivalent."*

Consequently, damage has been deduced in a simplified way, that is, by associating the categories of exposed receptors to the *potential damage*. In practice, three potential damage classes have been identified: (i) D4—very high potential damage, (ii) D3—high potential damage, (iii) D2—medium potential damage, and (iv) D1—moderate (or null) damage, which are described in **Table 1**.

As a consequence of the damage ranking in four classes, the risk has been assessed by means of a matrix method. Risk categories have been deduced by those proposed by the former decree of the Prime Minister (D.P.C.M. 29.09.98, which contains the guidelines for the adoption of urgent countermeasures against natural hydro-geological risks, regarding hazard assessments).


**Table 1.** List of the classes of damage, according to the act of MATTM ([3], p. 24).

require a quantitative estimation of risk. The cited handbook addresses the map of assets at risk (i.e., the distribution of population, vulnerable groups, and buildings at risk) more than

Index of Proportional Risk (IRP) Flood-Risk Assessment Model and Comparison to Collected Data

http://dx.doi.org/10.5772/intechopen.79443

21

The same *Floods Directive Reporting Schemas* [9], which should be followed by countries in reporting to European Commission, allow different methods for reporting, and quantitative estimation is optional. Actually, according to the reporting schema, damage can be indicated (i) as a range, (ii) as a percentage of the total GDP for the flood event, (iii) by classes (Insignificant, Low, Medium, High, Very high), or (iv) by means of other numerical measure indicative of the degree of (potentially) adverse consequences, leaving a wide choice for

Therefore, the report of quantitative damage is not compulsory, qualitative estimations are widespread, even if the risk formula, which implies the quantification of risk, is often reported

There are several practical problems with matrix approach, either with respect to the guide-

First, the scales shown in the matrix are ordinal (i.e., rank-ordered); consequently, mathemati-

Second, the risk matrix generally shows only probability and consequence, and rank risks by that pair of measures; vulnerability is implicitly considered in the matrix or set equal to a

Third, communication to people may reveal to be captious; for example, the damage in D4 class in **Table 1** is not necessarily twice the damage of D2 class, in spite of the damage class

Fourth, it is questionable if risk matrices actually improve decision making. Cox has been particularly critical of risk matrix and hazard ranking systems, concluding that "*Applying portfolio optimization methods instead of risk prioritization ranking, rating, or scoring methods can* 

The present limitations of risk mapping approach adopted in the implementation of EFD can be reviewed and in the next step of "*…reconsideration and updating…*" in the flood directive.

Actually, the *management plans for flood risk (PGRA)* should be periodically reviewed, and if necessary updated, taking into account "*…the likely impacts of climate change on the occurrence of floods*" (EFD, art.14). Italian legislation provides the time limits to review the preliminary flood-risk assessment (before 09/22/2018 and at a later stage, every 6 years), the hazard maps and flood risk (before 22.9.2019 and thereafter every 6 years) as well as the Management Plans

To this aim, ISPRA edited "*Methodological proposal for updating hazard and risk maps for risk mapping*" [11]. The document aims at proposing some approaches, taken from scientific literature,

to be implemented in the revision and updating of the flood-risk maps.

to "*risk maps.*"

implementation.

constant value.

indication.

in official documents (see [9], p.23).

cal operations with ordinal scales are meaningless.

*achieve greater risk-reduction value for resources spent"* [10].

(before 22.09.2021 and thereafter every 6 years).

lines of the EFD or theoretical.

**Figure 1.** The matrices adopted in PGRA, by Po basin District Authority. Hazard classes P1, P2, and P3 refer to the return period indicated in EFD (P1 for T = 20–50; P2 for T = 100–200; P3 for T = 500).

As far as the Po basin District Authority ([4], p. 17) is concerned, the risk is assessed by the combination of the damage and hazard classes, through a matrix approach. The rows show the damage classes and the columns the hazard levels, that is, the probability of flood occurrence. The implementation of this matrix allowed associating a risk class to each exposed element (receptor).

To distinguish the different impacts in terms of human life and anthropic activities risk, three different matrices were used, each for a different flooding process: (i) first matrix (a) in **Figure 1** refers to flooding in main rivers, (ii) second matrix (b) to lake flooding and Apennines rivers, and (iii) third matrix (c) refers to plane secondary rivers.

On the basis of hazard and flood-risk maps, the District Authorities prearrange the flood-risk management plans (PGRA), coordinated at the level of river basin district.
