TREND ANALYSIS OF MULTIDECADAL DATASETS OF AIR AND SEA SURFACE TEMPERATURES WITHIN THE SOUTHEASTERN BAY OF BISCAY

Abstract

The results of the trend analysis of air and sea surface temperatures measured in Donostia-San Sebastian, southeastern Bay of Biscay, are described within this contribution. The all temperature data series belongs to the Meteorological Observatory of Igeldo (AEMET) (43 degrees 18' N, 02 degrees 02' W; at 252 m above the mean sea level). The time series extends from 1928 to 2008, representing 81 years of daily maximum and minimum air temperatures. The sea surface temperature (SST) dataset, measured in a nearly daily basis at 10 a.m, at the Aquarium of Donostia-San Sebastian (43 degrees 19' N, 02 degrees 00' W), extends from 1947 to 2008; representing 62 years of data. In order to remove fluctuations due to time-scales of less than a year (such as seasonal variability), an annual moving average has been calculated. Subsequently, a trend analysis has been performed with the annual air and sea surface temperature data, by linear regression fitting and by minimising absolute deviation. Globally, a slightly decreasing trend (-0.003 degrees C.year(-1)) can be observed, for the whole of the SST time series (1947-2008). In contrast, a warming trend of 0.008 and 0.011 degrees C.year(-1) is detected for the minimum and maximum air temperature series (1928-2008), respectively. However, the analysis of both time series, in a decadal basis, shows a remarkable warming trend since the mid 1980s. Such increase is of 0.019 and 0.026 degrees C.year(-1) for the annual averaged minimum and maximum air temperatures; whilst it is of 0.019 degrees C.year(-1), for the annual averaged SST.