Frequent readers of this blog may be aware that different natural hazards often happen at the same time; periods of drought may coincide with periods of extreme heat, and very strong winds can come with extreme precipitation. However, it is probably even more common that one type of hazard takes place at many locations simultaneously. For example, when rivers flood, surrounding rivers often flood at the same time. That flooding in different rivers can happen at the same time sounds trivial but is ignored in almost all flood research, because floods are typically assessed and managed at the scale of individual river basins.
Risk finance (..) can be improved by accounting for how flood risks extend beyond the borders of individual drainage basins
In a recent paper, we tried to systematically expose to what extent river floods in Europe are connected with floods of other rivers. A recently released database of floods over the period 1960 through 2010 allows studying this. Studying over 170.000 flood events occurring in complex spatial patterns across Europe (see movie), we demonstrate that the flood synchrony scale -the distance over which multiple rivers flood near synchronously- far exceeds the size of individual drainage basins and varies regionally. The paper also shows that flooding has become more spatially extensive in recent decades. Thus, flood risks are correlated well beyond the individual drainage basins for which flood hazards are typically assessed and managed. Risk finance, flood forecasting, and interpretations of flood trends can be improved by accounting for how flood risks extend beyond the borders of individual drainage basins.
Paper: Berghuijs et al. (2019). Growing spatial scales of synchronous river flooding in Europe. Geophysical Research Letters, 46. https://doi.org/10.1029/2018GL081883
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