Zu heiß und zu nass – über den Zusammenhang dieser gegensätzlichen Wetterextreme

Too hot, too wet - about the connection between these contrasting weather extremes: If local weather patterns are placed in a temporal climatic context, this results in more or less strong deviations in temperature conditions, which can sometimes amount to several degrees. The corresponding spatial patterns then often show an alternation of positive and negative anomalies, which tend to line up along the lines of longitude in mid-latitudes. Extreme weather conditions such as heat waves, for example, which lead to marked positive temperature deviations in one place, can trigger severe flooding elsewhere as a result of cold air outbreaks to the south. This is due to the course of the high-altitude winds (jet stream). The stronger these winds blow into Europe from westerly directions, the stronger the weather influence from the North Atlantic and the less likely extreme weather conditions are in Europe. If, on the other hand, the transport across latitudes increases in the spatial course of the high-altitude winds, weather conditions can remain stationary for longer, which can favour the occurrence of opposing weather extremes. Retrospective analyses of the correlation between large-scale weather patterns over Europe and the occurrence of local extreme weather conditions show that meridional weather patterns account for a higher proportion of weather variability, particularly in the warm season, thus increasing the probability of the occurrence of hydroclimatic extremes (heat waves and heavy rainfall).