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A study of twelve centuries of climate reveal Europe should prepare for wetter as well as drier summers as the climate warms.

An international team of researchers have published a study exploring how summer temperature and drought have varied in Europe in the past  - which can tell us more about summer heatwaves and droughts in the present and future.

The study places recent summer drought in the context of the past 12 centuries revealing that, throughout history, northern Europe has actually tended to get wetter during warmer periods, with southern Europe tending to get drier.

The study reveals that improving our understanding of the relationship between summer heat and drought is critical, not only to understanding likely future drought patterns, but to summer flood risks in northern parts of Europe too.

The new study, published in Environmental Research Letters, explores the historical picture of summer temperature and drought using weather measurements going back to the 18th century, tree-ring- reconstructions of temperature and drought going back to the 9th century and climate model simulations.

The past picture of drought and temperature was compared to climate simulations using the same climate models that are used to predict future climate change. This comparison revealed that the climate model simulations, which show a simple  relationship for Europe, where warm summers are also dry, do not match the picture revealed by the historical records which show that a large a part of Europe has received more rainfall , not less, when it has been warm in the past 12 centuries.

Project leader Dr Fredrik Charpentier Ljungqvist, Associate Professor at Stockholm University, said: “These new findings are important as we are able to see for the first time that the relationship between summer temperature and drought in modern weather measurements has persisted for at least 12 centuries. We can also see that the 20th century wetter trend in northern Europe, and the drier trend in southern Europe is common over the longer-term perspective,”

Study author Mary Gagen, Professor of Geography at Swansea University said: “We’ve known for a long time that climate is changing due to human activity, but we also know that not everywhere experiences just simple warming. What we need to do now is to add detail to our understanding of a changed world, what parts will experience wetter climate extremes, which parts drier. When we experience summers of extreme temperatures in Europe, we need to understand where are they likely to be accompanied by drought and where are they likely to be accompanied by flooding. Studies like ours, that look at the past co variability of both temperature and rainfall, help us fill in the details of our changing climate.”

Going on to discuss the climate model results Dr Ljungqvist said: “Crucially, our study shows that the strong link between warm and dry periods being simulated in the climate models could be too simple. It’s not a picture backed up by the tree-ring and weather records. The climate simulations seem to underestimate how big a portion of Europe actually experiences wetter summers when the climate is warmer.

“It implies a possible exaggeration in the climate models of temperature-driven drought risk in parts of northern Europe under global warming. But this also means that the models may well underestimate future excessive rainfall, with associated flood risks, in northern Europe.”

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