Author(s): Johan Casselgren; Robert Granstrom

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Abstract: In the spring of 1995, the lower reaches of the Piteå River (Piteålven) experienced an exceptional flood, with reported stages of about 7 m above low-water levels compared to a typical 3-4 m spring rise. The event caused widespread inundation in the communities of Vidsel and Älvsbyn and created near-damage conditions for critical bridge infrastructure. This extended abstract outlines an ongoing reconstruction of the 1995 flood by combining (i) local, community-facing stage observations from the River Online monitoring system and (ii) snow-depth and precipitation observations from the Swedish Meteorological and Hydrological Institute (SMHI). A central hypothesis is that the magnitude and rapid rise of the 1995 flood were strongly conditioned by the pre-flood liquid water content of the seasonal snowpack, which governs both runoff efficiency and the sensitivity to rain-on-snow inputs. We present the data integration workflow, a stage reconstruction approach based on correlation between River Online stage and Sikfors power-plant discharge, and a snowpack representation that emphasizes snow bulk density and resulting snow water equivalent (SWE). The contribution is a transferable, data-driven methodology for attributing extreme spring floods in largely unregulated Nordic rivers, with direct implications for early-warning and flood preparing measures as well as decision support in real-time.

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Year: 2026