Compound coastal storms become more common by 2100
Heavy rain and storm-driven high seas already coincide far more than by chance, and that pairing is projected to increase along most coasts.
Source
More meteorological events that drive compound coastal flooding are projected under climate change
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Compound coastal storms become more common by 2100
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The global median return period of 17 years is roughly 20 times more likely than independence.
The global median return period of 17 years shows that in the majority of coastlines around the world, ocean and inland meteorological extremes are strongly correlated and roughly 20 times more likely to co-occur compared to if they were independent.
Under RCP8.5, drivers co-occur more frequently along 60% of the global coastline by 2100.
Under a high emissions scenario (RCP8.5), the meteorological drivers of compound flooding are projected to co-occur more frequently along 60% of the global coastline by the end of this century (Fig.
What they did
Using ERA-Interim (1980–2014) and six CMIP5 models, the authors fitted copulas to 3-day precipitation and meteorological tide (surge plus 0.2× wave height) along the global coastline, then compared 1970–2004 with 2070–2099 under RCP8.5.
What they found
Present-day median joint return period is 17 years (~20× more likely than independence at 365 years). Under RCP8.5, drivers co-occur more often along 60% of coasts; global median return period falls 20% (events 26% more probable). North of 40°N, frequency averages 2.6× present (ΔT = −61%). Precipitation changes explain 77% of the frequency shift.
The limits
What it doesn't show
The analysis excludes large river catchments and mean sea-level rise. Only six CMIP5 models and ~100 km coastal spacing. Meteorological tide omits full inundation modelling. Dependence change is small compared with marginal precipitation change.
Key terms
- Compound flooding
- Coastal flooding when high meteorological tide and heavy rain/runoff coincide or closely follow.
- Meteorological tide
- Storm surge plus a simple wave-setup term, excluding long-term sea-level rise.
- Joint return period
- Average wait for concurrent extremes; lower values mean stronger dependence or higher hazard.
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Quiz yourself
Present-day median joint return period of rain plus meteorological tide is about:
Common questions
If rain and surge were independent, what joint return period is expected?
365 years for the chosen percentiles; observed median 17 years shows strong dependence.
Does the paper include sea-level rise?
No: it isolates meteorological drivers so SLR is an extra, compounding factor in reality.
Where does concurrence increase most?
Northern Hemisphere coasts above 40°N, averaging 2.6 times present by 2100.
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