North Atlantic SSTs lead UK summer droughts
A North Atlantic freshwater–SST pathway leads UK summer rainfall and streamflow droughts by about 1.5 years.
Source
Oceanic drivers of UK summer droughts
What they did
Authors correlated 1950–2020 HadISST-based subpolar-cold-anomaly and North Atlantic Current indices with UK SPI3 and catchment SSI3, then traced the ocean–atmosphere chain through four extreme summers (1976, 1995, 2018, 2022) using ERA5 winds and salinity.
What they found
Winter SCA and summer NAC SST patterns correlate with UK precipitation and with streamflow except in groundwater-dominated southeast catchments, at ~1.5-year lag. Extreme drought years share a poleward-shifted jet, a northward NAC, and a preceding winter SST tripole tied to subpolar freshening.
The limits
What it doesn't show
Only four extreme case years support the full salinity-to-drought chain, correlations can be non-stationary, and southeast groundwater catchments do not show the streamflow link, so this is not yet an operational forecast system.
Key terms
- SPI3
- Standardised Precipitation Index for 3-month accumulations.
- SSI3
- Standardised Streamflow Index for 3-month accumulations.
- SCA-JFM
- Winter index of the North Atlantic subpolar cold SST anomaly / tripole.
- NAC-JJA
- Summer index of a northward-shifted North Atlantic Current SST front.
- Teleconnection
- Remote statistical and dynamical link between ocean conditions and UK drought.
Flashcards
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Quiz yourself
UK summer hydrology lags the winter subpolar cold SST anomaly by about:
Common questions
Why look at oceans instead of weather models?
Oceanic variability has longer memory than the atmosphere, offering lead times beyond current summer forecast skill.
Do rainfall droughts always become streamflow droughts?
No; southeast groundwater catchments buffer meteorological drought so SSI3 does not follow the SST indices.
What four summers illustrate the pathway?
1976, 1995, 2018 and 2022—years with the highest NAC-JJA values.
What starts the chain?
Summer freshwater into the subpolar North Atlantic stratifies the surface and helps build the winter SST tripole.
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