Oceanic conditions associated with Euro-Atlantic high pressure and UK drought

Persistent atmospheric high pressures can lead to long-lasting droughts and heatwaves with severe societal and environmental impacts, as evident in summer 2018 in Europe. It is known that oceanic and atmospheric features connected with the tropical Pacific influence the atmospheric circulation regimes over the North Atlantic/European sector leading to blocking high pressures in the cold season. Here we show that in the warm season, different combinations of sea surface temperatures in the North Pacific and the North Atlantic are associated with distinctly different atmospheric circulation patterns over northwest Europe some three months later. While most studies are restricted to atmospheric variables, for the UK we also investigate the hydrological impact and find that the effect of the preferred seasonal storm tracks is more clearly seen in regional streamflow observations than in precipitation, presumably because streamflows integrate the influences of precipitation and evapotranspiration. These relationships open up the possibility of skilful statistical forecasts for much of spring to autumn, which will usefully complement the currently available skilful winter forecasts based on general circulation models. Our results deliver new understanding of the truly global driving processes of UK droughts and highlight the potential for improved early warning for the wider European domain.