Rare precipitation extremes are projected to increase relatively more than common extremes under future climate change. However, it is unconfirmed whether these projected differences in relative change are observable in historical precipitation data. Therefore, this study investigated whether rare precipitation extremes have changed differently from more common ones during the period 1951 to 2010, in Western Europe. The differences in change between rare and common extremes (Drare-common) and its correlation with temperature is analysed, using daily temperature and precipitation data. The Drare-common values are calculated based on the relative change of a specific return level estimated by three methods: the Full series, the Generalized Extreme Value (GEV) and the Metastatistical Extreme Value (MEV) distribution. A correlation with daily temperature is obtained by analysing first all day temperatures and compare these with the pattern in the Drare-common values. Secondly, the temperatures at the days of the annual extremes is analysed.
The results indicate that, on average for Western Europe, historical precipitation extremes have increased in magnitude by 3.0 up to 5.4%, depending on the method. Regional variations are present in Western Europe, showing negative relative changes for the most southern regions. A Drare-common for Western Europe equal to 1.0 and 2.3%pt is obtained, for respectively the MEV and GEV method, indicating that the rarest precipitation extremes have increased more in magnitude compared to the common extremes. However, a comparison of extremes based on the time series length using the Full series indicated no difference in relative changes for return levels of 0.1 and 10 years. A statistically significant correlation between the Drare-common and temperature is obtained between the results of the GEV and Tmax and MEV method and Tmin. This correlations suggests observing a relative high Drare-common value in a region in which the change in maximum temperature is low and the change in the minimum temperature is high, depending on the method used. Analysing the temperatures during annual extremes showed an increase in both the minimum and maximum temperature on the days of the annual extremes, despite a shift from warmer to colder months in which annual extremes occur. When dividing the annual extremes into common and rare, it was concluded that a higher increase in temperature is observed during common annual extremes compared to the rare annual extremes.
It is recommended to analyse this phenomenon in more recent years. To understand the behaviour of precipitation extremes in greater depth, other driving factors causing precipitation to become extreme could be studied. Examples of these driving factors include atmospheric water vapor and the temperature in regions where precipitation is generated.