Recent trends and temporal behavior of thermal variables in the region of Castilla-Leon (Spain)

The behavior of temperatures in the region of Castilla-Leon in Spain was explored in a study of trend analyzes of the regional thermal anomalies in the zone. The work was developed in two steps: in the first, the working data series were refined, completed and homogenized. The variables addressed in these series were the maximum, minimum and mean temperatures corresponding to 38 weather observatories representative of the whole regional area and their length spanned the 1931-1996 period. Homogenization was carried out by applying the methodology established by Alexandersson and Moberg (1997). Once the homogeneous series had been constructed, in a second phase we analyzed their temporal behavior from regional anomaly series. To do so, the values of the anomalies were calculated at each of the selected stations - for the 1945-1996 period - from the mean monthly, seasonal and annual values of the 1961-1990 period. Then, following the methodology described by Jones et al. (1982) and Jones and Hulme (1996), the representative values for the whole region were determined. The results obtained for the whole period analyzed (1945-1996) indicated that, for a confidence interval of 95%, increasing trends are only seen for the maximum and mean winter values. Outside this threshold, the trend found was of the same sign in summer, whereas trends were decreasing for all the variables for their equinoctial seasons. By contrast, the behavior of temperatures in the 1972-1996 subperiod was striking; the annual maximum, minimum and mean temperatures displayed a certain increasing trend for that confidence interval. This was confirmed with the seasonal values, above all for spring and summer, and also (secondarily) those of winter and autumn. Thus, over the past 25 years analyzed there has been an increasing trend of about 0.05 degree C/year in the values of the maximum, minimum and mean temperature anomalies, both annual and seasonal.