SFA V: Earth-System modelling

The models used to project floods, droughts, and water availability are built from equations derived in the laboratory or in small field plots – at scales of meters – but are applied on grid cells of kilometers, covering whole continents. This scale mismatch is a key reason why different global water models give strikingly different answers to the same question. This project systematically compares many models from international intercomparison projects, all run under identical conditions, to uncover which relationships between climate inputs and water outputs actually hold at the scale where the models operate. A special twist: the team will also apply "information field theory," a statistical method originally developed for mapping the cosmos, to Earth-system data. The project is multi-scale because the meter-versus-kilometer mismatch is its central subject, and interdisciplinary because hydrology, climate-impact research, and astrophysical data science join forces.

Many complex systems – the climate, financial markets, entire galaxies – show behavior that repeats in characteristic ways. "Recurrence analysis" is a mathematical technique that detects such repeating patterns in measurement series and can reveal hidden regime changes. This project extends the technique so it can distinguish patterns on different time scales and detect how fast processes influence slow ones and vice versa. The new toolkit will be applied to two very different questions: how water-cycle models behave across scales from single river catchments to the globe, and how supermassive black holes regulate star formation in their host galaxies – whether through narrow jets or broad winds. The project is multi-scale because detecting cross-scale coupling is its core purpose, and interdisciplinary because one and the same mathematical method illuminates both Earth-system science and galaxy evolution.