Fluvial flood events can generate substantial impacts on people, places, economies, infrastructure, livelihoods, and ecosystems (e.g. river and floodplain hydroecology; fluvial pollutant transport). Climate change can influence the seasonality of flooding, and in cold or mountainous environments in Europe there are concerns that a shift from a snowmelt-dominated to a rainfall-dominated flow regime can occur. This could have profound impacts on water management strategies, i.e. flood risk mitigation, drinking water supply and hydro power. In addition, cold climate hydrological systems exhibit complex interactions with catchment properties and large-scale climate fluctuations making the manifestation of changes difficult to detect and predict. It is therefore essential to define key flood drivers to develop understanding of possible changes in flood seasonality to input into management and mitigation strategies This study specifically defines changes in flood seasonality over recent decades across several near-natural catchments in Scandinavia using circular statistics and trend tests. Results reveal patterns of strong seasonality in flooding for snowmelt-dominated catchments, with a single peak occurring in spring and early summer (March through June). However, close to the Atlantic coast and in the southern catchments flood peaks are more equally distributed throughout the year. In particular, decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows are revealed here, with 5-35% of the catchments showing significant changes at p=0.05. Analyses of seasonal mean daily flows support these findings and show that higher percentages (5-60%) of the analysed catchments show statistically significant flow changes (p=0.05). Changes in the timing of annual flood events also suggest a shift in flow regime from snowmelt-dominated to rainfall-dominated with 25% of the catchments showing earlier flood peak timing. Regionally consistent patterns suggest a first order climate control as well as a local second order catchment control which causes inter-seasonal variability in the streamflow response.
- flood seasonality
- circular statistics
- Mann Kendall test
- trend analysis
Matti, B., Dahlke, H., Dieppois, B., Lawler, D., & Lyon, S. (2017). Flood seasonality across Scandinavia: Evidence of a shifting hydrograph? Hydrological Processes, 31(24), 4354–4370. https://doi.org/10.1002/hyp.11365