An analysis of the temporal behavior of the annual and seasonal frequencies of extreme maximum daily
temperature values on the Spanish Central Plateau is performed. With the daily data on maximum temperatures measured at 14 weather stations, between 1961 and 2003, we constructed a series of maximum daily temperature anomalies for each of the observatories and in the study zone, and also in the two subzones into which the Central Plateau can be divided. To determine the highest and lowest extreme values of the maximum daily temperature anomalies, the P05 and P95 percentiles of the anomaly series were considered as thresholds. Next we constructed the series of annual frequencies of days with the highest and lowest extreme values of maximum daily temperature anomalies. Trend analysis of these series revealed that during the period studied the annual frequency of the lowest extreme cases of maximum daily temperature anomalies has tended to decrease while that of the highest ones has tended to increase. From an analysis of the temporal evolution of the annual frequencies it may be deduced that a variation in the trend occurred around 1972, variation previously established for other variables (pressure, annual mean temperature, etc.) in the area of study. The results obtained upon considering the interval of time between 1973 and 2003 indicate that the trend was the same as that obtained for the whole period studied but the level of confidence is higher. Finally, it may be seen that spring and summer are the seasons that most affect the behavior of the annual frequencies of the extreme maximum daily temperature values.
