A theory of dynamical systems for the Baltic Basin

The Earth´s atmosphere is generally considered to be part of a chaotic system. As such, it is reasonable to believe that also sub-systems of Earth´s atmosphere like the NAO (North Atlantic Oscillation) will be chaotic. According to this theory, it is impossible to predict the exact time evolution of the NAO, or for that matter precipitation, over more than a few weeks into the future. Consequently, rainfall-runoff processes will also, at a regional scale where NAO is essential, follow chaotic characteristics. Long-term predictions of climate and runoff become excluded by chaotic definition. Repeated short-term forecasts, however, are possible based on information about the chaotic system. The tool to resolve the chaotic system and the theoretical background for this is called dynamical systems theory.

The Baltic Sea is the largest brackish water body on Earth and consequently of great international concern. The drainage basin of the Baltic spans 14 countries and 85 million people, a majority of them living in big cities like St. Petersburg, Copenhagen, Helsinki, Tallinn, Riga, Vilnius, Warsaw, and Stockholm. During recent years the Baltic has experienced large-scale water quality degradation. The water quality depends on the quality of runoff from surrounding drainage areas but critically also on the so called Major Baltic Inflows (MBI) that freshen the Baltic Sea water with influx of saline and oxygen-rich water from the North Sea depending on specific sequences of winds and atmosphere pressure. These short-lived (in the order of one to three weeks) freshening episodes may be related to NAO and thus also to chaotic properties of the atmosphere. If runoff from surrounding drainage basins and MBIs into the Baltic Sea follow chaotic characteristics, systematic investigation of these processes based on dynamical systems theory may provide insight to how water quality of the Baltic water may change in time. In turn, this may explain the precarious future situation of marine ecosystems in the Baltic.

Progress in dynamical systems theory related to regional-scale hydrological processes that can be related to climatic variation has, however, been hampered by the fact that almost no long-term runoff or other water balance components exist at the regional scale. A second inter-related problem is that runoff from, e.g., small-scale catchments, is often contaminated by noise or local climate related variations. Large-scale basins provide a great advantage in this context. The integrated runoff from large basins effectively filters out small-scale variation and leaves a large-scale climatic imprint. Consequently, runoff at large scales provides insights to regional climatic variability and is important for the understanding of long-term major climatic variation patterns. 

The objective of the present research program is to combine recently acquired knowledge from regional-scale modeling of runoff from the Baltic Basin with a cause-effect relationship of climatic observables in the time scale of annual to the centennial period (50-100 years). The application is a joint program between researchers at SMHI, where major efforts have been made to model regional-scale runoff from the Baltic Basin, and researchers from Lund University that have specialized in developing dynamical systems theory to understand hydrological variation driven by climate. The project therefore addresses a fundamental research issue within climate change/variation and the cause-effects of such changes/variations.

Status (October 2005): A large data base of climatological data for the Baltic basin has been compiled, quality-controlled and analysed in general terms. Non-linear analysis and dynamical systems modelling is presently ongoing.

Duration: 2003-2005

Funded by: VR (Swedish Research Council)

Responsible at SMHI: Jonas Olsson

External partners: Lund University