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| Titel |
Validity of Cost-Benefit Analysis for Flood Prevention Projects: Insights from Sensitivity Analysis |
| VerfasserIn |
F. Grelot, J. S. Bailly, N. Saint-Geours |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028577
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| Zusammenfassung |
| Abstract Cost-Benefit Analysis (CBA) is widely promoted as a tool for discussing
efficiency of flood management policies. It gives rise to a global indicator, the Net
Present Value (NPV), which allows the discussion of allocating regional, national, or
supra-national fundings to local projects. Concerning flood management policies, CBA
relies on damages avoided approach which consists in measuring the benefits of a
project by differentiating without and with project situations in term of expected
damages.
One of the under-explored area is uncertainty and sensitivity analyses linked to CBA
based on damages avoided approaches. The main reason relies on the complexity of
analysing precision of the NPV indicator, which is a combination of hydrological, hydraulic,
geographic and economic knowledge, and which depends on the precision of the underlying
information. In hydrology, uncertainties result from interpolation or extrapolation in space
and in time of some gauging stations. In hydraulics, uncertainties come from outputs
of the hydraulic model (water level errors) combined to topographical data when
mapping submersion duration and water levels (interpolation errors, DTM errors).
In economics, uncertainties depend on multi-scale network effects considered in
damages modelling. On a first modelling level, elementary space units segment the
studied area. These units, denoted stakes, can be points, lines or polygons. In this
case, damages supported by stakes are only depending on their exposition to the
hazard realization, independently from others stakes. On a second level, stakes may
be seen as a system of elementary units (e.g. a farm is a system containing the
farm buildings and cultivated areas). In that case, damages on a particular stake can
affect others since they are related to them (an agricultural co-operative outside the
flooded areas is affected by damages encountered in the farms located in the flooded
areas).
Nevertheless, uncertainty analysis should be systematically performed as a necessary
complement of any CBA: how could projects efficiency be discussed on a synthetic indicator
which we cannot precise the validity? Sensitivity analysis, as it serves to define hierarchically
the required precision (i.e. quality) for each input data, is also a necessary step. A particular
issue in the CBA for flood prevention is linked to the various uses of the geographical
space for each one of the chained models. The sensitivity analysis should take into
account another particular point: the output scale of the economic models can be
local or global, include only one event or several events. Thus, a link between data
resolutions (e.g. spatial resolution) and economic model output precisions has to be
developed.
In this paper, we present two complementary analysis based on a case study in the Orb
delta, South of France. Firstly, a sensitivity analysis is performed on a CBA of a flood
reduction project. This analysis was based on Sobol indices calculated with a Monte-Carlo
approach, giving a hierarchical view of the inputs, data or parameters, impacting the CBA
results. In the same time, this analysis allows the computation of a confidence band for the
global NPV of the project, considering uncertainties on inputs. In a second step, an analysis
on the use of mapped intermediary and local outputs of CBA such as mapped damages for a
particular event, and mapped annual expected damages are presented. Spanning
spatial resolutions on these outputs and considering imprecisions resulting from the
chained model, this analysis exhibits appropriate and avoided spatial resolutions
for local outputs. This latter result arises new questions on CBA mapped output
communication.
Keywords flood risk, cost-benefit analyis, uncertainty modelling, sensitivity analysis, spatial
simulation, multiscale estimation, map. |
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