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1. Definition
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Name
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DROUGHT
INDEX
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Brief
definition
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The
index provides a description, on the regional level,
of the frequency and severity of drought.
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Unit of measure
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adimensional index
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2.
Position within the logical framework DPSIR
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Type
of Indicator
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State.
Represents a typical climatic 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, devised in Portugal. Along
with the soil loss index and the climate index, it
contributes to producing a scale of the state of health
of soil and water resources and consequently to the
elaboration of development strategies compatible with
the resources available in a given area.
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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.
Within
Agenda 21 the drought index is relevant to Chapter
12 - Management of fragile ecosystems: combating desertification
and drought.
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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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Drought
can be characterised on the basis of three different
parameters: I) water deficit, in the sense of the
"magnitude" of drought (lack of water below
a certain threshold value), or as a measure of the
severity of drought (relation between the maximum
water deficit and the mean water deficit); ii) the
mean number of drought years (relation between the
number of drought years and the total number of years
under consideration); iii) the surface area affected
by drought (which is a measure of the extent of the
phenomenon).
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Benchmarks
Indication of the values/ranges of value
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Threshold
values distinguishing the increasing severity of drought:
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Methods
of measurement
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Since
characterising drought implies a certain degree of
subjectivity in the analysis, a simple methodology
was employed based on the definition of a threshold
below which a certain degree of drought occurs. This
threshold value is obtained from the probability value
that the level of precipitation will not be above
the annual average. The distribution of drought is
represented by means of the Thyessen polygons figuring
around the stations where rainfall is measured.
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Limits
of the indicator
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These
are mainly linked to the type of methodology adopted
to represent the distribution of drought. The method
of Thyessen polygons is a technique that, because
of its extreme rigidity, is not widely used. In any
case, since the level of standardisation of spatial
interpolation techniques is not very high at the moment,
problems arise for all the indicators of this type.
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Linkages
with other indicators
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The
Climate index, along with the Soil loss 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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The
necessary data are annual rainfall statistics, obtainable
from the various stations located in the area under
study, for a sufficiently representative period of
time.
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Data
sources
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Data
can be obtained from the various regional, national
or international institutions involved in collecting
and elaborating this kind of data, or, if not available,
it must be collected by the user with the help of
the meteorological stations spread around the area
under study.
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Availability of data
from national and international sources
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The required data is
generally easily available and is reasonably cost-effective.
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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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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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