Contributions of synoptic and planetary-scale drivers to precipitation extremes

Large-scale precipitation extremes in the mid-latitudes arise from the interaction of multiple synoptic and planetary-scale circulation features. While a considerable body of literature exists on individual drivers, comparability and joint attribution across different spatial scales—from planetary to synoptic—remain challenging. Here, we use an object-based, spatio-temporal framework to identify and characterise key large-scale drivers of precipitation extremes like atmospheric rivers (ARs), frontal systems, blocking, cut-off lows, and anticyclonic and cyclonic Rossby wave breaking (RWB) using multi-decadal ERA5 reanalysis data. Each circulation driver is identified using established object-tracking algorithms applied to the respective diagnostic fields. The detected circulation objects are linked to spatiotemporal extreme precipitation objects. This allows assessing the relative and joint contributions of different synoptic- and planetary-scale drivers to extreme precipitation intensity, duration, and spatial extent across seasons and hemispheres. By analysing synoptic- and planetary-scale features within a consistent framework, the work aims to provide insights into the multi-scale dynamical controls on precipitation extremes, supporting dynamical attribution and improving understanding of how trends in dynamics may reflect on trends in precipitation extremes.