The observed trend in unusual daily mean temperatures over Germany from 1949 to 2018 and their relationships to major climatic drivers

Abstract

Unusual events are detected by the statistical changes in ‘extremes’, when extreme anomalies persist through the temporal and spatial interactions of the variable of interest. To identify the occurrences of unusual daily mean temperature events in 3- and 5-day sequences, a statistical method based on an “outlyingness” function is proposed in this study. This function is based on the geometrical position of a point on the multivariate set. To illustrate the methodology, this study uses daily mean temperature records from 18 observation stations across Germany (1949–2018). The findings indicate discernible changes in the frequency of unusual events at the stations, mostly during the boreal winter months between the first and last 35 years of the study period. A wide range of temperature anomaly averages (− 12 °C to + 12 °C) are produced by the interaction of series between warm and cold conditions, which affects the occurrence of disappearing days. While this is happening, the unusual warming is more pronounced on days that emerge from both the 3- and 5-day sequences, with temperature anomaly averages ranging from + 4 to + 12 °C. The Atlantic Multi-Decadal Variability and the Arctic Oscillation/North Atlantic Oscillation, respectively, are both implicated in the unusual surface warming over Germany. The disappearance days of unusual events do not exhibit statistically significant correlations with climatic indices, suggesting a possible anthropogenic effect. The emphasis of this study is on the necessity of determining whether unusual events in daily temperature anomalies across Germany can be attributed to anthropogenic factors.