Flood seasonality across Scandinavia—Evidence of a shifting hydrograph?

Abstract

Fluvial flood events have substantial impacts on humans, both socially and economically, as well as on ecosystems (e.g., hydroecology and pollutant transport). Concurrent with climate change, the seasonality of flooding in cold environments is expected to shift from a snowmelt-dominated to a rainfall-dominated flow regime. This would have profound impacts on water management strategies, that is, flood risk mitigation, drinking water supply, and hydro power. In addition, cold climate hydrological systems exhibit complex interactions with catchment properties and largescale climate fluctuations making the manifestation of changes difficult to detect and predict.Understanding a possible change in flood seasonality and defining related key drivers therefore is essential to mitigate risk and to keep management strategies viable under a changing climate.This study explores changes in flood seasonality across near-natural catchments in Scandinavia using circular statistics and trend tests. Results indicate strong seasonality in flooding for snowmelt-dominated catchments with a single peak occurring in spring and early summer (March through June), whereas flood peaks are more equally distributed throughout the year for catchments located close to the Atlantic coast and in the south of the study area. Flood seasonality has changed over the past century seen as decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows with 5-35% of the catchments showing significant changes at the 5% significance level. Seasonal mean daily flows corroborate those findings with higher percentages (5-60%) of the catchments showing statistically significant changes. Alterations in annual flood occurrence also point towards a shift in flow regime from snowmelt-dominated to rainfall-dominated with consistent changes towards earlier timing of the flood peak (significant for 25% of the catchments). 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.

Climate and rivers

“…Importantly, Hannaford and Buys () emphasise the dependence of some results on study period and caution against upscaling the results from small drainage basins to the regional scale because of the spatial heterogeneity of observed flow regime trends. In nearby Scandinavia, Matti, Dahlke, Dieppois, Lawler, and Lyon () have found changes in flood seasonality over the last century as demonstrated by decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows. Further, and as for the case of western North America (Fritze et al, ), it is likely that temperature‐driven shifts from snowmelt‐ to rain‐dominated flow regimes account for the observed alterations in annual flood occurrence and timing (Matti et al, ).…”

“…In nearby Scandinavia, Matti, Dahlke, Dieppois, Lawler, and Lyon () have found changes in flood seasonality over the last century as demonstrated by decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows. Further, and as for the case of western North America (Fritze et al, ), it is likely that temperature‐driven shifts from snowmelt‐ to rain‐dominated flow regimes account for the observed alterations in annual flood occurrence and timing (Matti et al, ). At the European scale, Bloeschl et al () point to a possible climate change‐related signal in flood regimes noting that earlier spring snowmelt floods across north‐eastern Europe are a consequence of higher temperatures, whereas later winter floods around the North Sea and some sectors of the Mediterranean are likely to be associated with delayed winter storms with earlier soil moisture maxima driving earlier winter floods in western Europe.…”

Are Detected Trends in Flood Magnitude and Shifts in the Timing of Floods of A Major River Basin in India, Linked To Anthropogenic Stressors?

“…(3) A transition of mixed flood regime to a more pluvial regime whereas nival catchments transition towards a more mixed response was observed. Matti et al (2017) Scandinavia (i) Sites: 59 catchments across Scandinavia (ii) Period of analyses: A record length of 54-122 years (1892-2014) (iii)Data: Seasonal maximum daily flows in a hydrological year (iv) Approach: Circular or directional statistics were used to assess flood seasonality and modified Mann-Kendall trend test was used for trend analysis…”

Future evolution and uncertainty of river flow regime change in a deglaciating river basin

“…With near-surface air temperature projected to rise over the coming decades (Collins et al, 2013) future changes in river flow regimes in response to cryosphere change could have wide-ranging socio-economic and environmental impacts. Long-term reductions in meltwater inputs will disrupt the supply of water available for irrigation (Nolin et al, 2010;McDowell and Hess, 2012;Carey et al, 2014;Baraer et al, 2015). Increased inter-annual and intra-annual flow variability will threaten infrastructure projects such as hydroelectric power stations (Laghari., 2013;Gaudard et al, 2014;Carvajal et al, 2017).…”