Attack of the extreme floods

Abstract

knew what was heading for his hometown: category-5 Hurricane Irma, which had already battered much of the Caribbean. He got on the plane anyway. "It was me, the pilot and a few Disney tourists who just didn't care, " he says.Irma's heavy rains and powerful winds killed dozens of people across Florida. For Wahl, who rode out the storm in his family's one-bedroom apartment, the experience was a rare chance to witness first-hand a phenomenon he has long worried about: extreme sea levels -what happens when storm surges, high tides and waves combine.Extreme sea-level events can send water pouring over coastal barriers, swamping people's homes and drowning crucial infrastructure. They've happened, for example, in New Orleans in Louisiana and the surrounding region -still recovering from more than US$100 billion in damages caused by Hurricane Katrina in 2005 -and in Jacksonville, Florida, where Irma swamped parts of the city under 2 metres of water, trapping residents and closing bridges and the city's international airport.Globally, mean sea level is rising by just over 3 millimetres a year, as glaciers and ice caps melt and warming ocean water expands. Researchers have typically focused on understanding the causes and rate of that rise. But swelling seas are also expected to affect extreme sea levels, with devastating effects. In the coming decades, 100-year floods -those that have a 1% chance of hitting in a given year, or an average return interval of 100 years -could occur as often as every year or two (see 'The coming floods'). Across Europe, the cost of coastal flooding could rise by more than a factor of 20 by the year 2100 (ref. 1). And in some regions, the intensity of what constitutes a 100-year flood will become much more severe.Wahl and a small band of colleagues say that more scientists need to pay attention to the shifting nature of these calamitous events and how they will affect those living near the coast. Such floods will be one of the biggest The cruellest seasExtreme floods will become more common as sea levels rise. © 2 0 1 8 M a c m i l l a n P u b l i s h e r s L i m i t e d , p a r t o f S p r i n g e r N a t u r e . A l l r i g h t s r e s e r v e d .

Reconstructing patterns of coastal risk in space and time along the US Atlantic coast, 1970–2016

“…The alongshore mean rate derived from sea-level rise shows close agreement with the mean recent shoreline-change rate, suggesting that our simplified bathtub representation of hazard is a reasonable proxy on a multidecadal timescale (Fig. 5), even though bathtub models tend to underestimate shoreline erosion rates along barrier coastlines (Lorenzo-Trueba and Ashton, 2014;Wolinsky and Murray, 2009). Individually, not all counties register rising risk trajectories over time.…”

“…Our estimation is effectively a "bathtub model" of change, controlled only by topography with no incorporation of wave-driven sediment transport or other shoreline dynamics. Bathtub models tend to underpredict shoreline erosion rates in wave-dominated, sandy barrier settings, such as those of the US mid-Atlantic (Lorenzo-Trueba and Ashton, 2014;Wolinsky and Murray, 2009). However, for this exercise, our method is useful for its simplicity -especially given the spatial scales under consideration -and for the independent estimation of shoreline change that it provides.…”

“…Risk reduction in developed coastal zones is a global challenge (Parris et al, 2012;Sallenger et al, 2012;Witze, 2018;Wong et al, 2014). Risk can be expressed as a function of hazard, exposure, and vulnerability.…”

Phronesis at the Human-Earth Nexus: Managed Retreat

“…Although caused by global warming, the rising mean sea-level is not a uniform steric phenomenon (Horton et al, 2020) because of ocean dynamics and mass distribution (ice). Significant regional differences will occur (Grinsted et al, 2015), including shifts of extreme events wherever the mean sea-level is subject to substantial changes (Witze, 2018). For example, water levels in Hamburg or London (Western Europe) may rise by 0.8 m and drop in Oulu (Northern Europe, Bay of Bothnia) by 0.1 m. Related to the mean sea-level changes, the likelihood of the combined height of astronomical tides and storm surges [extreme sea-levels (ESL)] shifts.…”

Reconstructing patterns of coastal risk in space and time along the US Atlantic Coast, 1970-2016

“…Risk reduction in developed coastal zones is a global challenge (Parris et al, 2012;Witze, 2018;Wong et al, 2014). In general terms, risk can be expressed as a function of hazard, exposure, and vulnerability (NRC, 2014;Samuels and Gouldby, 2009).…”