The Variations and Trends of the Surface Air Temperature in the Northeastern of Spain from Middle Nineteenth Century Onwards

Abstract

A new and more extensive homogenised and gridded data set of surface air temperature (NESAT v.2) has been generated for Northeastern Spain. The aim of this compilation has been to extend, temporally, the preliminary estimations of the long-term variations and trends of the Catalonian temperature (Brunet, et al., 1999). The improved meteorological network for this region, composed of 23 records of non-urban stations, has been used to analyse the 1869-1998 period. To obtain a new regional time-series of monthly average of daily mean temperature, the gridded procedures proposed by Jones et al. (1986) have been applied to the adjusted data. Hence, a rectangular 3degrees X 4degrees latitude-longitude box, that covers our region from 40degrees-43degrees N and 0degrees-4degrees E, has been employed to accomplish this purpose. The seasonal and annual variations and trends of these data have been estimated by using usual statistical techniques (linear trends, low-pass filters, change point detection, etc.). The results show a moderate but highly significant regional warming (0.9degrees C) in the whole period, largely contributed by winter trend, in agreement with results observed at the global scale (i. e. Peterson, et al., 1999; Jones, et al., 1999). However, this warming has not occurred in a steady, monotonic fashion, but different thermal periods have been recorded. First, an initial long steady period of moderate but highly significant warming (0.01degrees C/year) has been observed between 1869-1949. Second, and intermediate short cool phase lasting until mid-1970s, associated with significant (95% confidence level) but moderate cooling (-0.03degrees C/year). Third, an unprecedented fast, abrupt, strong and highly significant warming (0.07degrees C/year) has been recorded from the mid-1970s to the present. Furthermore, six out of the ten warmest years of this record have been registered in the last decade (1989-1998).