Dimensionality of Scandinavian river flow regimes

A river flow regime describes an average seasonal behaviour of river flow, usually representing a set of long-term monthly mean values. Seasonal patterns of flow can be regular, repeating in principle the same pattern from year to year, or irregular, i.e. alternating between a couple of different regime types during individual years. By tradition, a river flow regime has been considered as a static characteristic that does not change in large temporal scale, yet this may be an oversimplification with regard to constantly changing environmental conditions. Such a "static" description of a flow regime, based on long-term mean values is in discrepancy with the dynamic character of the system described. The dimension of this system in terms of fractal and intrinsic dimensions has been investigated on an example of Scandinavian runoff series by different methods: from a simple graphic method to determine the fractal dimension to empirical orthogonal function (EOF) and entropy-based aggregation to outline the number of patterns necessary for representing the regimes of different intrinsic dimension of a set of point data. The series studied demonstrated a variety of fractal and intrinsic dimensions that were well in agreement with the stability character of the investigated regime types. The less stable the regime, the higher were its fractal and intrinsic dimensions and the number of variables required for its description.