Climate-driven variability in the occurrence of major floods across North America and Europe

Abstract

Concern over the potential impact of anthropogenic climate change on flooding has led to a proliferation of studies examining past flood trends. Many studies have analysed annual-maximum flow trends but few have quantified changes in major (25-100 year return period) floods, i.e. those that have the greatest societal impacts. Existing major-flood studies used a limited number of very large catchments affected to varying degrees by alterations such as reservoirs and urbanisation. In the current study, trends in majorflood occurrence from 1961 to 2010 and from 1931 to 2010 were assessed using a very large dataset (>1200 gauges) of diverse catchments from North America and Europe; only minimally altered catchments were used, to focus on climate-driven changes rather than changes due to catchment alterations. Trend testing of major floods was based on counting the number of exceedances of a given flood threshold within a group of gauges. Evidence for significant trends varied between groups of gauges that were defined by catchment size, location, climate, flood threshold and period of record, indicating that generalizations about flood trends across large domains or a diversity of catchment types are ungrounded. Overall, the number of significant trends in major-flood occurrence across North America and Europe was approximately the number expected due to chance alone. Changes over time in the occurrence of major floods were dominated by multidecadal variability rather than by long-term trends. There were more than three times as many significant relationships between major-flood occurrence and the Atlantic Multidecadal Oscillation than significant long-term trends.

Robust Adaptation to Multiscale Climate Variability

“…Peaks for the American River time series are apparent at 2.3 and 15 years and in the LBDA time series at approximately 8, 20, and 64 years. A detailed analysis of these time series is beyond the scope of this paper, but we note that the high amplitude and long time periods of the quasiperiodic oscillations they exhibit are consistent with analyses of LFV in other hydroclimate systems (Hodgkins et al, 2017;Kiem et al, 2002;Swierczynski et al, 2012;Woollings et al, 2014). A detailed analysis of these time series is beyond the scope of this paper, but we note that the high amplitude and long time periods of the quasiperiodic oscillations they exhibit are consistent with analyses of LFV in other hydroclimate systems (Hodgkins et al, 2017;Kiem et al, 2002;Swierczynski et al, 2012;Woollings et al, 2014).…”

Recent trends in the frequency and duration of global floods

“…Ward et al (2016) and Emerton et al (2017) have previously demonstrated the role of ENSO in modulating global floods. In addition, Hodgkins et al (2017) demonstrated recently that AMO has a significant negative (positive) relationship with 25-and 50-year flood occurrence for large (medium) catchments in North America (Europe).…”

Trend detection in river flow indices in Poland

“…Banasik et al 2013;Ilnicki et al 2014;Kędra 2017;Miler 2015;Somorowska 2017) or small regions (Niedźwiedź et al 2015;Ruiz-Villanueva et al 2016;Sen and Niedzielski 2010), with one notable exception of Wrzesiński and Sobkowiak (2018) who analysed long-term changes (but not trends) in flow regime of 159 flow gauges with a good geographical coverage in Poland. Polish rivers were not included in several pan-European (Hannaford et al 2013;Stahl et al 2010) or global (Hodgkins et al 2017) studies on trend detection, perhaps due to restrictive data sharing policy . In summary, a need for a comprehensive trend detection study for Polish river flows is well motivated.…”