European drought’s relationship to global SST

So far on this blog I’ve described natural modes of variability across the North Atlantic basin like the NAO, the AMO and AMOC and their related climatic impacts. They are all associated with specific climatic patterns of temperature and precipitation across large areas, and I’ve mentioned and showed illustrations of these in my previous posts. In this post I will only focus on the drought impact and try to give a summary of the factors controlling droughts across Europe.

A study by Ionita et al. (2012) looked at variability of European summer drought and its relation to global sea surface temperature (SST) by using the Palmer drought severity index averaged over the European region (see figure below).

 

This time series show the strong interannual and decadal variability of European drought. The authors show that winter SST has a strong impact in determining drought variability over Europe in the upcoming summer through different large-scale teleconnection patterns. By the use of correlation analysis they reveal the existence of three coupled modes of summer drought pattern and winter SST anomalies with different timescales:

1.    The first coupled mode represents the long-term warming trend in global SST caused by anthropogenic greenhouse gasses, in addition to a tripole-like pattern in SST resembling the positive phase of the NAO.

2.    The second coupled mode is associated with an inter-annual SST pattern in the Pacific which resembles the cold phase of ENSO (La Niña) together with the decadal fluctuation in extratropical SST resembling the Pacific DecadalOscillation (PDO).

3.    The last coupled mode is associated with strong multidecadal variability in SST across the Atlantic basin which corresponds with the AMO, also for the interannual variability. In a previous post I described how the AMO exerts a strong influence on European summertime climate, including drought. As they write in the paper: “According to Briffa et al. (2009) the summers of 1921, 1976, and 1990 were among the driest in the last 250 years, all these dry summers occurring during a cold North Atlantic phase of the AMO.”

I’ve previously described the NAO- and the AMO’s impact of heat and drought on the European climate. It now turns out that drought across Europe is associated with four different modes of variability! (NAO, ENSO, PDO and AMO). Drought is not an easy thing to define given the complexity of the phenomenon, and there also exists several types of drought. So to say that drought across Europe is determined exactly by these four modes of variability is of course just looking at the big picture.