Resumo

LABAJO, ÁNGEL L. et al. Definition and temporal evolution of the heat and cold waves over the Spanish Central Plateau from 1961 to 2010. Atmósfera [online]. 2014, vol.27, n.3, pp.273-286. ISSN 0187-6236.

The temporal behavior of the annual frequency of heat and cold waves observed between 1961 and 2010 is established for the Spanish Central Plateau and for the two sub-areas in it. The series of daily maximum and minimum temperature anomalies for the working areas were calculated from the daily data concerning temperature anomalies. The thresholds of these series of anomalies, determined by the P₁₀ and P₉₀ percentiles values, were obtained. Heat waves occur when there are two or more consecutive days on which the maximum and minimum temperature anomalies are simultaneously greater than the values of the thresholds obtained for the P₉₀ percentile. The heat waves that affected the Spanish Central Plateau and the two sub-areas during the period of time considered were identified and their monthly and annual frequencies were obtained. Likewise, a cold wave is considered to have occurred when there are two or more consecutive days on which the maximum and minimum temperature anomalies are simultaneously lower than the thresholds established by the corresponding P₁₀ percentiles. The cold waves occurring in the study area were identified and their monthly and annual frequencies in the study period were established. According to the results, the months with highest number of heat waves between 1961 and 2010 were May (25 waves) and June (23 waves). Trend analysis of the series of annual frequencies indicates that there was an increasing trend towards the occurrence of heat waves, with a confidence level greater than 99%. The linear model established indicates that an increase had occurred in the frequency of heat waves in the Spanish plateau of the order of 0.6 waves every 10 years. Regarding cold waves, these were detected in each month of the year and their frequency ranged between eight and 16 events per year. The months with lowest number of cold waves were April (nine), July (eight) and August (nine), and the months with the highest number were March, May, June and October, with 16 cold waves. The years with the highest number of cold waves were 1969, 1971 and 1977, with seven cases. In the other years the annual rate was between one and six. Trend analysis of the series of annual frequencies indicated that there was a decreasing frequency of cold waves, at the confidence level of 99%. When a linear model was considered for the Spanish Central Plateau a decreasing frequency of the cold waves of the order of 0.54 waves in every 10 years was observed from 1961 to 2010.

Palavras-chave : Anomaly; temperature; heat wave; cold wave; frequency; trend.