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1. Definition
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Name
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RAINFALL
EROSIVITY
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Brief
definition
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Intensity
of 30 millimetres of rain with a return period of
100 years
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Unit of measure
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mm/hour
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2.
Position within the logical framework DPSIR
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Type
of Indicator
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State.
The indicator represents a typical condition of the
area under study.
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3.
Target and political pertinence
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Objective
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The
main objective is the identification of desertification
prone areas, with particular reference to degradation
of soil and water resources.
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Importance
with respect to desertification
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This
indicator is part of a set of tools to identify and
mitigate land degradation, developed in Portugal.
As such it contributes to producing a scale of soil
loss and consequently, to the elaboration of development
strategies compatible with the resources available
in the given area.
Within
Agenda 21 rainfall erosivity is relevant to Chapter
12 - Management of fragile ecosystems: combating desertification
and drought.
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International
Conventions and agreements
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The
UNCCD emphasizes the fact that combating desertification
must be tackled within the general framework of actions
to promote sustainable development.
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Secondary objectives
of the indicator
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4.
Methodological description and basic definitions
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Definitions
and basic concepts
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The
intensity of 30 millimetres of rain with a return
period of 100 years, i.e. once the intensity per hour
of all rainfall reaching 30mm is calculated, the lowest
one with a return period of 100 years is identified.
The greater the intensity, the highest is the probability
of experiencing extreme events.
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Benchmarks
Indication of the values/ranges of value
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Four
classes of erosive power have been distinguished;
- <60mm/h
- 60 - 67.5mm/h
- 67.5 - 75mm/h
- >75mm/h
A
score is attributed to each class and is then multiplied
by the score of the other indicators to obtain the
soil loss indicator.
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Methods
of measurement
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Limits
of the indicator
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Limitations
to the indicator are linked mainly to the difficulty
of interpolating the data and applying it to different
spatial scales, because the techniques used to do
so have a low level of standardisation. Moreover,
there are problems of application to areas where data
is not available in sufficient quantity and quality
(100 year series)
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Linkages with other
indicators
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Together with the indices
defining soil type, Vegetation
cover and slope, this indicator contributes to defining
the soil loss index. The soil loss index, along with the climate
index and the Drought
index, each of which is linked to a specific process to
do with degradation, have a direct relationship to water resources
and are combined into a single index (the sum of the three
indices), which, by means of a Geographical Information System
(GIS) serves to map desertification prone areas.
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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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Data
on rainfall over a period of at least 100 years.
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Data
sources
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Meteorological
data can be obtained from various regional, national
or international institutions involved in the collection
and elaboration of such data.
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Availability of data
from national and international sources
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The data required is
not always easily available, but if it is, the cost-effectiveness
is reasonable.
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6.
Institutions that have participated in developing the indicator
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Main
institutions responsible
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DGF
- Direcçao-Geral das Florestas. Ministèrio da Agricultura,
do Desenvolvimento Rural e das Pescas, Portugal.
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Other
contributing organizations
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7.
Additional information
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Bibliography
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National
Action Programme to combat desertification - Portugal
17 June 1999.
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Other
references
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http:
//www.dgf.min-agricultura.pt.
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Contacts Name and address
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Direcçao-Geral das Florestas
Av.a Joao Crisotomo, n. 28-5.1069-040 Lisboa- Portugal
Tel: +351.1.312 49 58
FAX: +351.1.312 49 89
Email L dgf.web@mail.telepac.pt
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