Temperature and Precipitation Variability and Trends in Northern Spain
273
Only for winter, there is a fourth significant EOF, representing the northern
Mediterranean coast.
5.2 Principal Trends and Abrupt Changes
This section deals with identifying the presence of trends and abrupt changes in the
PC time series. For these series, the lag-one correlation is very small (no significant
at 95% level). The right-hand side of Figures 3 - 5 also show the result of the MannKendall test applied to the first principal component series.
The characterisation of the periods as wet or dry has been done using 10 year
moving averages. Figs. 7a and b show the seasonal series with the corresponding
smoothed series, identifying the longer term variability. The first winter series,
associated with Andalusia and "Peninsular Interior" begins with a slightly dry
period between 1900 and 1930. There is a relatively rainy period from then until
1945. Then, and during the 1950s, it follows a drier than normal period. The 1960s
and, to a lesser extend, the 1970s were very rainy. The 1980s are characterized as
a dry period. For the spring there is a significant decreasing trend in this region. For
summer, the first years of the 20'h century were quite humid. For autumn the most
significant fluctuation ocurred during the dry 30s.
For the Mediterranean area the significant decreasing trend is remarkable which
occurred during winter in the Northeastern area and for spring in the last years. Also
for spring, we find important fluctuations in the dry 60s and the rainy 70s.
At the Northern coast, there is a slight increasing trend of winter precipitation.
During spring, it is remarkable the low precipitation values during the decades of
40s and 50s, and in the 90s. Autumn precipitation shows low values from 1900
until 1930 and in the decade of the 80s.
5.3 Discussion of Precipitation Results
Annual precipitation basically is related to the precipitation from September to May
as the correlation between the annual and seasonal PC series shows. The correlation
ranges around 0.55 for the Interior and Andalusia and Cantabric coast. All
correlation coefficients between annual and seasonal PC series for Andalucia, the
interior stations, and the Cantabric region are significant, although the correlation
between summer and annual series of these areas is smaller than the other seasonal
correlations. For these areas, the winter is the most important season on the annual
totals, whereas, for the Mediterranean region, the autumn (correlation with annual
data of 0.67) is the most influential one.
The results agree partially with conclusions drawn by other researchers. There
were relatively wet periods in the Mediterranean until 1914, in 1930s, and in 1960s
and 70s for the Mediterranean area (Maheras, 1988; Maheras and Koliva-Machera,
1990; Maheras et aI., 1992). The humid 1930sin the Spanish region seems to be
widespread over Europe, at least for the latitudes below 50 0 N (Brazdil et aI., 1985),
273
Only for winter, there is a fourth significant EOF, representing the northern
Mediterranean coast.
5.2 Principal Trends and Abrupt Changes
This section deals with identifying the presence of trends and abrupt changes in the
PC time series. For these series, the lag-one correlation is very small (no significant
at 95% level). The right-hand side of Figures 3 - 5 also show the result of the MannKendall test applied to the first principal component series.
The characterisation of the periods as wet or dry has been done using 10 year
moving averages. Figs. 7a and b show the seasonal series with the corresponding
smoothed series, identifying the longer term variability. The first winter series,
associated with Andalusia and "Peninsular Interior" begins with a slightly dry
period between 1900 and 1930. There is a relatively rainy period from then until
1945. Then, and during the 1950s, it follows a drier than normal period. The 1960s
and, to a lesser extend, the 1970s were very rainy. The 1980s are characterized as
a dry period. For the spring there is a significant decreasing trend in this region. For
summer, the first years of the 20'h century were quite humid. For autumn the most
significant fluctuation ocurred during the dry 30s.
For the Mediterranean area the significant decreasing trend is remarkable which
occurred during winter in the Northeastern area and for spring in the last years. Also
for spring, we find important fluctuations in the dry 60s and the rainy 70s.
At the Northern coast, there is a slight increasing trend of winter precipitation.
During spring, it is remarkable the low precipitation values during the decades of
40s and 50s, and in the 90s. Autumn precipitation shows low values from 1900
until 1930 and in the decade of the 80s.
5.3 Discussion of Precipitation Results
Annual precipitation basically is related to the precipitation from September to May
as the correlation between the annual and seasonal PC series shows. The correlation
ranges around 0.55 for the Interior and Andalusia and Cantabric coast. All
correlation coefficients between annual and seasonal PC series for Andalucia, the
interior stations, and the Cantabric region are significant, although the correlation
between summer and annual series of these areas is smaller than the other seasonal
correlations. For these areas, the winter is the most important season on the annual
totals, whereas, for the Mediterranean region, the autumn (correlation with annual
data of 0.67) is the most influential one.
The results agree partially with conclusions drawn by other researchers. There
were relatively wet periods in the Mediterranean until 1914, in 1930s, and in 1960s
and 70s for the Mediterranean area (Maheras, 1988; Maheras and Koliva-Machera,
1990; Maheras et aI., 1992). The humid 1930sin the Spanish region seems to be
widespread over Europe, at least for the latitudes below 50 0 N (Brazdil et aI., 1985),