Understanding future changes in the frequency of dry days

• Applicant: Professor Dr. Stephan Pfahl
• Subject Area: Atmospheric Science
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569816948

Future changes in the occurrence of drought are partly related to changes in the frequency of dry days, that is days without precipitation. Global climate models project a complex spatial pattern of changes in the dry day frequency (DDF), but the underlying processes are currently not well understood. The goal of this project is to investigate how dynamic and thermodynamic processes as well as specific atmospheric precursors related to moist convection shape this pattern of DDF changes. To this end, a set of diagnostics will be applied to output of a large ensemble of global Community Earth System Model simulations. A physics-based scaling that was originally developed for the analysis of extreme precipitation will be adapted to decompose DDF changes into dynamic and thermodynamic contributions. To overcome limitations of such physics-based diagnostics in the representation of small-scale processes like moist convection, we will additionally apply statistical models, namely a machine learning method based on decision trees as well as explainable artificial intelligence in the form of generalized additive models. These statistical models incorporate the influence of additional precursors such as convective available potential energy and convective inhibition. Finally, the influence of weather regimes in the North Atlantic and European sector on DDF changes will be studied. In this way, we will improve our fundamental understanding of an important driver of future drought changes, which are expected to have severe impacts on society and ecology.

• DFG Programme: Research Grants