Joint estimation of trend in bulk and extreme daily precipitation in Switzerland

Precipitation is crucial for water supply and energy generation in the Alps. However, heavy precipitation can also lead to natural disasters. It is therefore essential to understand the changes in both mean and extreme precipitation in order to develop effective adaptation and mitigation strategies. This study jointly models the observed long-term trends in both the bulk and extremes of daily precipitation distribution in Switzerland by employing a non-stationary version of the Extended Generalized Pareto distribution (EGPD). The EGPD allows us to model the entire non-zero precipitation range while remaining consistent with extreme value theory in its lower and upper tails.. We incorporated the non-stationarity by allowing the parameters of the distribution to vary with two covariates, time and sea surface temperature, and used a bootstrap approach for uncertainty assessment and to assess the significance of the modeled trends. The results indicate that extreme precipitation has increased in all seasons, while mean precipitation has only significantly increased in winter in northern Switzerland. This increase in winter precipitation is attributed to both a positive trend in the frequency and in the intensity of wet days precipitation.