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MJ. Esteban-Parra, D. Pozo-Vazquez, F.S. Rodrigo, Y. Castro-Diez
average temperature, is an agent in environmental changes (Hansen et aI., 1995).
Predicted increase in global temperature based on numerical models, is between 0.6
and 0.4° C over the next 25 years (IPCC, 1995), together with effects, which are not
very well understood, so, for example, a most critical need is to investigate whether
global warming will cause changes in regional precipitation, and some authors have
underlined the need for researching the precipitation variability (e.g., Shuttleworth,
1996). This implies the need to examine local changes and to relate then to different
possible environmental impacts of the climatic change in each region. Furthermore,
to improve our knowledge of the climate, research is needed on local and regional
scales (Karl et aI., 1989). The use of empirical methods can reveal major patterns
and provide qualitative estimates of the form and range of the regional climate
change useful to validate climatic models with a physical basis (Giorgi and Mearns,
1991).
In the present work, the mean temperature and precipitation records throughout
Spain are analysed, with an special emphasis in the Northern Spain. The climatic
studies over this region have particular interest, due to the geographical position of
the Iberian Peninsula, between the Atlantic Ocean and the Mediterranean Sea, and
between the continents Africa and Europe. In addition, this region is located in the
circumpolar vortex border (Capel Molina, 1981) and its climate is closely linked
with the atmospheric circulation. The climatic variability of this area is also of
interest due the current problems provoked by droughts and other extreme events,
which have been discussed by some authors (Katz and Brown, 1992) as good
indicators of the climatic change and by the adverse predictions of the models in the
Mediterranean area (IPCC, 1995). It is important to identify regions with similar
behaviour, detect and quantify possible changes and relate them with possible causal
mechanics .The present paper undertakes this task for the case of Spain.
2 Data
The database used in this study includes annual and seasonal mean, maximum and
minimum air temperature and precipitation for 40 Spanish localities, covering the
Iberian Peninsular area and Baleares Islands (Fig. 1.). They were selected from 65
series supplied by the Instituto Nacional de Meteorologfa (INM), attending quality
criteria. Precipitation database is completed with some grid points of Portugal. The
temporal coverage for temperature is 1880-1995 and for precipitation is 1900-1997.
Most of the stations have not changed their position, but only for a few of them
do we know the metadata related to methods and instruments. The absolute
homogeneity of the records was evaluated using the Thom and Bartlett tests (Thom,
1966; Mitchell, 1966). These methods were also used to check the relative
homogeneity, analysing the difference (for temperature) or ratio (for precipitation)
series obtained for neighbouring locations (Bradley et aI., 1985, Rhoades and
Salinger, 1993).
Homogeneity problems are most common in temperature records. Some of the
MJ. Esteban-Parra, D. Pozo-Vazquez, F.S. Rodrigo, Y. Castro-Diez
average temperature, is an agent in environmental changes (Hansen et aI., 1995).
Predicted increase in global temperature based on numerical models, is between 0.6
and 0.4° C over the next 25 years (IPCC, 1995), together with effects, which are not
very well understood, so, for example, a most critical need is to investigate whether
global warming will cause changes in regional precipitation, and some authors have
underlined the need for researching the precipitation variability (e.g., Shuttleworth,
1996). This implies the need to examine local changes and to relate then to different
possible environmental impacts of the climatic change in each region. Furthermore,
to improve our knowledge of the climate, research is needed on local and regional
scales (Karl et aI., 1989). The use of empirical methods can reveal major patterns
and provide qualitative estimates of the form and range of the regional climate
change useful to validate climatic models with a physical basis (Giorgi and Mearns,
1991).
In the present work, the mean temperature and precipitation records throughout
Spain are analysed, with an special emphasis in the Northern Spain. The climatic
studies over this region have particular interest, due to the geographical position of
the Iberian Peninsula, between the Atlantic Ocean and the Mediterranean Sea, and
between the continents Africa and Europe. In addition, this region is located in the
circumpolar vortex border (Capel Molina, 1981) and its climate is closely linked
with the atmospheric circulation. The climatic variability of this area is also of
interest due the current problems provoked by droughts and other extreme events,
which have been discussed by some authors (Katz and Brown, 1992) as good
indicators of the climatic change and by the adverse predictions of the models in the
Mediterranean area (IPCC, 1995). It is important to identify regions with similar
behaviour, detect and quantify possible changes and relate them with possible causal
mechanics .The present paper undertakes this task for the case of Spain.
2 Data
The database used in this study includes annual and seasonal mean, maximum and
minimum air temperature and precipitation for 40 Spanish localities, covering the
Iberian Peninsular area and Baleares Islands (Fig. 1.). They were selected from 65
series supplied by the Instituto Nacional de Meteorologfa (INM), attending quality
criteria. Precipitation database is completed with some grid points of Portugal. The
temporal coverage for temperature is 1880-1995 and for precipitation is 1900-1997.
Most of the stations have not changed their position, but only for a few of them
do we know the metadata related to methods and instruments. The absolute
homogeneity of the records was evaluated using the Thom and Bartlett tests (Thom,
1966; Mitchell, 1966). These methods were also used to check the relative
homogeneity, analysing the difference (for temperature) or ratio (for precipitation)
series obtained for neighbouring locations (Bradley et aI., 1985, Rhoades and
Salinger, 1993).
Homogeneity problems are most common in temperature records. Some of the