A Differential Response of Northeastern Spain to Asymmetric Trends in Diurnal Warming Detected on a Global Scale

Abstract

The aim of this paper is to detect, estimate and characterise the existing variations and trends in surface air temperature in the Northeast of Spain, from the mid-nineteenth century onwards. To achieve this purpose, a new homogenised and gridded dataset of monthly mean maximum and minimum temperatures has been generated improving the spatial and temporal coverage of a previous study (Brunet, et al., 1999). The annual and seasonal averages of this data are analysed for the entire period (1869-1998) and partial time subsections in search of time variations and trends, by using usual statistical techniques (linear regression, filtering, change point detection, etc.). Our results show a moderate warming over the Catalonian region during the overall period, either for daily maximum temperature (0.96degrees C) or daily minimum temperature data (0.82degrees C). However, the warming has not occurred in a steady and linear fashion, and several periods can be distinguished, the fast, abrupt, strong and highly significant warming observed from the mid-seventies to the present being the most remarkable. However, both maximum and minimum temperatures present quasi similar amounts of long-term warming leading to a slight but non-significant increase in DTR over the total period (0.14degrees C), in contrast with the reported ongoing reduction of day-night temperature differences found over several continental areas of the globe. Also, no diurnally asymmetrical changes have been observed for this region, in agreement with other regional-scale studies, but in disagreement with hemispherical and global findings.