The role of Rossby wave breaking for extreme and annual mean precipitation in (semi)arid regions

Precipitation can have large dual societal impacts in regions with a dry climate. On the one hand, extreme precipitation can induce catastrophic floods, and on the other hand, replenish scarce freshwater resources. In contrast to wet (extra)tropical regions, the atmospheric processes that govern the precipitation formation in dry subtropical and extratropical regions are often overlooked by the scientific community. In this study we investigate the role of Rossby wave breaking for precipitation in (semi)arid regions at the global scale. To this end, we quantify the contribution of Rossby wave breaking to extreme precipitation days and annual precipitation amounts in regions with different degrees of aridity. Rossby wave breaking is represented by potential vorticity (PV) streamers and cutoffs on isentropic surfaces using ECMWF reanalysis data, while for precipitation we also use an observational product. We show that the relevance of Rossby wave breaking for precipitation increases from humid to hyper-arid regions. Equatorward breaking Rossby waves contribute to a large fraction of precipitation extremes and annual amounts in regions on the poleward-westward flanks of the world’s most arid regions where most precipitation occurs in the cool season. In contrast, precipitation in the equatorward-eastward parts of these arid regions has a negative association with Rossby wave breaking, implying that the tropical forcing governs the precipitation formation which occurs in these regions predominantly in the warm season. Overall, this study shows that Rossby wave breaking is of key importance for precipitation in (semi)arid regions that are exposed to both flood hazards and drying under global warming.