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
Inspect source passages
North Atlantic SSTs lead UK summer droughts
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
The average lag from winter subpolar cold anomaly to next-year UK summer hydrology is about 1.5 years.
While the exact timing of the onset of the northward NAC shift pattern can vary depending on the duration of the cold and fresh anomaly in the subpolar region, the average lag between the subpolar cold anomaly in winter of the previous year and its impact on UK hydrology in the summer of the following year is ~1.5 years.
Correlations were computed over 1950–2020.
To understand the statistical relationships between SSTs patterns and UK hydrometeorology (SPI3 and SSI3) and other oceanic and circulation indices, we employ the Pearson correlation method over the common period of 1950—2020.
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.
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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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