Precipitation scenarios in the Central-Western Mediterranean basin
247
interpolation was necessary. For Italy, Spain, Portugal, Algeria, Tunisia, data quality
control has been performed by the respective Meteorological Services, using a
program of reduction or elimination of the error. As confirmed by the Italian
Meteorological Service, it is based on the control of the physical internal coherence
and the spatial inter-comparison. Data of other countries have been gathered from
the World Climatic Disc, produced by East Anglia University (World Climate Disc,
1992).
The sample area has been then subdivided into three latitude belts: northern (>
42~N), that includes 23 stations, central (38 N-4TN), with 21 stations, and southern
«38~N) with 15 stations. Both for the whole area and each belt the statistical
analysis has been effected.
Pressure field has been also examined, using data of 500 hPa height in Algiers
and Cairo, received from the respective Meteorological Services.
Table I. Stations used for yearly precipitation analysis
Ajaccio (France)
Algeri (Algeria)
Alghero (Italy)
Alicante (Spain)
Almeria (Spain)
Amendola (Italy)
Ancona (Italy)
Arezzo (Italy)
Barcelona (Spain)
Beia (Portugal)
Bellavista (Italy)
Bologna (Italy)
Bragan (Portugal)
Brindisi (Italy)
Cagliari (Italy)
Campobasso (Italy)
Catania (Italy)
Coimbra
(Portugal)
Cozzo (I taly)
Crotone (Italy)
Evora (Portugal)
Firenze (Italy)
Genova (Italy)
Gibilterra (Spain)
Ginosa (Italy)
Grosseto (Italy)
Leuca (italy)
Lisboa (Portugal)
Malta (Malta)
Marseille (France)
Mertola (Portugal)
Messina (Italy)
Milano (Italy)
Napoli (Italy)
Nimes (France)
Nice (France)
Oran (Algeria)
Palinuro (Italy)
Palma (Spain)
Perpignan (France)
Perugia (Italy)
Pescara (Italy)
Piacenza (Italy)
Pisa (Italy)
3 Analysis of PreCipitation Trend
Portaggr (Portugal)
Potenza (Italy)
Prizzi (Italy)
Ravenna (Italy)
Roma (Italy)
Sevilla (Spain)
Toulouse (France)
Torino (italy)
Trapani (Italy)
Trieste (italy)
Tripoli (Libya)
Tunisi (Tunisia)
Venezia (Italy)
Verona (Italy)
Viterbo (Ita I y)
To analyse precipitation pattern over the Central-Western basin a regional series has
been realised, from the available data, by Thiessen's technique (Chow, 1964). This
is used when, as in our study, the observations are not uniformly spaced over the
examined region and consists in weighting the datum of each station by a suitable
coefficient.
The obtained results indicate a decrease by a rate of -3.2 mm/year, that for the
whole period gives a reduction by 142 mm that is a reduction by about 21 %
(Piervitali et aI., 1998).
In order to obtain further confirmation of this results the Standardized Anomaly
Index (SAl) has been computed which is defined by
247
interpolation was necessary. For Italy, Spain, Portugal, Algeria, Tunisia, data quality
control has been performed by the respective Meteorological Services, using a
program of reduction or elimination of the error. As confirmed by the Italian
Meteorological Service, it is based on the control of the physical internal coherence
and the spatial inter-comparison. Data of other countries have been gathered from
the World Climatic Disc, produced by East Anglia University (World Climate Disc,
1992).
The sample area has been then subdivided into three latitude belts: northern (>
42~N), that includes 23 stations, central (38 N-4TN), with 21 stations, and southern
«38~N) with 15 stations. Both for the whole area and each belt the statistical
analysis has been effected.
Pressure field has been also examined, using data of 500 hPa height in Algiers
and Cairo, received from the respective Meteorological Services.
Table I. Stations used for yearly precipitation analysis
Ajaccio (France)
Algeri (Algeria)
Alghero (Italy)
Alicante (Spain)
Almeria (Spain)
Amendola (Italy)
Ancona (Italy)
Arezzo (Italy)
Barcelona (Spain)
Beia (Portugal)
Bellavista (Italy)
Bologna (Italy)
Bragan (Portugal)
Brindisi (Italy)
Cagliari (Italy)
Campobasso (Italy)
Catania (Italy)
Coimbra
(Portugal)
Cozzo (I taly)
Crotone (Italy)
Evora (Portugal)
Firenze (Italy)
Genova (Italy)
Gibilterra (Spain)
Ginosa (Italy)
Grosseto (Italy)
Leuca (italy)
Lisboa (Portugal)
Malta (Malta)
Marseille (France)
Mertola (Portugal)
Messina (Italy)
Milano (Italy)
Napoli (Italy)
Nimes (France)
Nice (France)
Oran (Algeria)
Palinuro (Italy)
Palma (Spain)
Perpignan (France)
Perugia (Italy)
Pescara (Italy)
Piacenza (Italy)
Pisa (Italy)
3 Analysis of PreCipitation Trend
Portaggr (Portugal)
Potenza (Italy)
Prizzi (Italy)
Ravenna (Italy)
Roma (Italy)
Sevilla (Spain)
Toulouse (France)
Torino (italy)
Trapani (Italy)
Trieste (italy)
Tripoli (Libya)
Tunisi (Tunisia)
Venezia (Italy)
Verona (Italy)
Viterbo (Ita I y)
To analyse precipitation pattern over the Central-Western basin a regional series has
been realised, from the available data, by Thiessen's technique (Chow, 1964). This
is used when, as in our study, the observations are not uniformly spaced over the
examined region and consists in weighting the datum of each station by a suitable
coefficient.
The obtained results indicate a decrease by a rate of -3.2 mm/year, that for the
whole period gives a reduction by 142 mm that is a reduction by about 21 %
(Piervitali et aI., 1998).
In order to obtain further confirmation of this results the Standardized Anomaly
Index (SAl) has been computed which is defined by