Changing climate both increases and decreases European river floods

Abstract

Climate change has led to concerns about increasing river floods resulting from the greater water-holding capacity of a warmer atmosphere 1 . These concerns are reinforced by evidence of increasing economic losses associated with flooding in many parts of the world, including Europe 2 . Any changes in river floods would have lasting implications for the design of flood protection measures and flood risk zoning. However, existing studies have been unable to identify a consistent continental-scale climatic-change signal in flood discharge observations in Europe 3 , because of the limited spatial coverage and number of hydrometric stations. Here we demonstrate clear regional patterns of both increases and decreases in observed river flood discharges in the past five decades in Europe, which are manifestations of a changing climate. Our results-arising from the most complete database of European flooding so farsuggest that: increasing autumn and winter rainfall has resulted in increasing floods in northwestern Europe; decreasing precipitation and increasing evaporation have led to decreasing floods in medium and large catchments in southern Europe; and decreasing snow cover and snowmelt, resulting from warmer temperatures, have led to decreasing floods in eastern Europe. Regional flood discharge trends in Europe range from an increase of about 11 per cent per decade to a decrease of 23 per cent. Notwithstanding the spatial and temporal heterogeneity of the observational record, the flood changes identified here are broadly consistent with climate model projections for the next century 4,5 , suggesting that climatedriven changes are already happening and supporting calls for the consideration of climate change in flood risk management.River floods are among the most costly natural hazards. Global annual average losses are estimated at US$104 billion 6 and are expected to increase with economic growth, urbanization and climatic change 2,7 . Physical arguments of increased heavy precipitation resulting from the enhanced water-holding capacity of a warmer atmosphere and

Joint Trends in Flood Magnitudes and Spatial Extents Across Europe

“…Finally, we estimate the regional diversity ( D j ) of flood generation processes by where j is the year, m is the flood generation process (1, …, 5), and f m , j is the relative frequency of process m in year j . We calculate D j for two regions, one in Western Europe where flood magnitudes have increased and one in Eastern Europe where they have decreased (Blöschl et al, 2019). For comparison, we estimate the spatial variance T j of the flood dates by the circular variance: where θ is the flood date converted into an angle between 0 (1 January) and 2 π (31 December), i is the station, and j is the year (Table S1).…”

Short-term flooding increases CH4 and N2O emissions from trees in a riparian forest soil-stem continuum

“…In future climate, the frequency of both flash floods and drought events is expected to be increased [48][49][50][51] . Although trees and other plants indicate the "forest ecosystem", their role within gas cycles is somehow underestimated 12 .…”

Event‐based classification for global study of river flood generating processes

“…Climate change, population growth, and urbanization all increase flood hazard and exposure (Hirabayashi et al, ). Large sample catchment studies already reveal historic trends in magnitude and frequency of floods over the past five to six decades in several areas around the world (Blöschl et al, ; Gudmundsson, Leonard, Do, Westra, & Seneviratne, ; Mallakpour & Villarini, ; Petrow & Merz, ). However, these trends in flood magnitude are not ubiquitous (Petrow & Merz, ) and cannot simply be connected to changes in precipitation (Sharma, Wasko, & Lettenmaier, ).…”

“…Blöschl et al () analysed how flood timing in Europe changes based on observed changes in flood generating processes thus allowing a conclusion about which processes are most influential in certain regions. Blöschl et al () similarly found trends in flood magnitude to be closely related to changes both in precipitation and soil moisture for several areas in Europe. All these methods are based on the average timing of flood generating process versus average timing of flood event occurrence.…”