Evaluation of long-term trends in spring onset in the Northern Europe using Singular Spectral Analysis
Results show few differences between the use of these two criteria for Stockholm series. Essentially, we find a first period, until 1860, with a significant trend to retard the spring onset, and a second period (from 1860 until the end of the records) with a significant tendency to advance the beginning of spring. Both periods show a similar absolute value (~0.7 days/decade). Our results are also in agreement with those obtained by other authors that use a different methodology.
The behaviour of spring onset in the Northern Europe seems to be related with the long-term variability of temperature. It is interesting to stand out that the variability observed in the onset of spring using these two indices is similar to that found using a very simple index, which can be computed as the first day of the year when the mean temperature exceeds on 5º C. Currently, we are studying the possibility of using this simpler index a precursor of the spring onset and their thermal characteristics.