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1. Definition
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Name
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FLOODING FREQUENCY
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Brief definition
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Type and probability
of occurrence of flooding
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Plain
area subjected frequently to flooding (photo by C. Kosmas)
|
|
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Unit of measure
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number
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2. Position within the
logical framework DPSIR
3. Target and political
pertinence
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Objective
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Management responses
can be used to control floods (structural) and their
impacts (non structural).
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Importance with
respect to desertification
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There are predominately
two types of meteorological events generating floods.
In large river basins flooding is usually seasonal
and frontal, while in small and medium sized basins,
isolated and localized very intense rainfall events
are produce flash floods. Such floods are common in
the Mediterranean area. Their rapid onset, which limits
warning procedures and emergency actions, produce
high velocity flood flows and the associated debris
load. Thus there is a high erosion potential contributing
significantly to the loss of soils and accelerating
the desertification process.
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International
Conventions and agreements
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Transboundary
and transnational legal agreements
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Secondary objectives
of the indicator
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Flood Forecasting
and Early Warning Systems
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4. Methodological description
and basic definitions
| Definitions
and basic concepts |
The
analysis of the probability of occurrence of floods
is traditionally based on the concepts of return period
and the frequency law of maximum flow discharges. The
return period associated with a defined flow is equal
to the number of years between floods that exceed that
flow. Given the stochastic nature of floods this number
of years is only an average value. The maximum discharge
frequency law is formed by discharges corresponding
to different return periods. In many Mediterranean basins
frequency laws are commonly composite, with a small
growth rate for low return periods and a strong rate
for medium and high periods. Finally, the ratio of ordinary
to extraordinary discharge of a river varies enormously
depending on the meteorological regime and basin characteristics. |
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Benchmarks Indication
of the values/ranges of value
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Highly dependant
on the expected flood of a given return period.
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Methods of measurement
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Frequency analysis.
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Limits of the
indicator
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The quality of
the indicator depends mainly on the number and distribution
of precipitation monitoring stations over the area,
particularly for extreme precipitation events, on
geomorphological data for the basin, vegetation cover
and land uses
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Linkages with
other indicators
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Rainfall,
Vegetation cover,
Land use type
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5. Evaluation of data
needs and availability
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Data required
to calculate the indicator
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Precipitation
statistics available from the various stations situated
in the area under study, vegetation cover, and land
use.
|
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Data sources
|
Necessary data
are usually available and accessible and the cost/benefit
ratio may be reasonable.
|
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Availability of
data from national and international sources
|
Data may be obtained
from various regional, national or international institutions
involved in the collection and the analysis of such
information.
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6. Institutions that
have participated in developing the indicator
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Main institutions
responsible
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Agricultural University
of Athens
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Other contributing
organizations
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Universities of
Lisbon, Murcia, Basilicata, Amsterdam, Leeds
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7. Additional information
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Bibliography
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Geeson, N., Brandt,
J., and Thornes, J., 2001. Mediterranean Desertification:
A mosaic of processes and responses. J. Wiley &
Sons, London, 439 p.
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Other references
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Follett, R., and
Stewart B., 1985. Soil erosion and crop productivity.
American Society of Agronomy. Madison Winscosin. USA.
Conacher, A.,
and Sala, M., 1998. Land Degradation in the Mediterranean
Environments of the World: Nature and Extent, Causes
and Solutions. J. Wiley & Sons, Chichester, 491
p.
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Contacts Name
and address
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Agricultural University
of Athens,
Laboratory of Soils and Agricultural Chemistry,
Iera Odos 75,
Athens 11855, Greece
Dr Constantinos
Kosmas
email: lsos2kok@aua.gr
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