Drought and floods in Europe: it is proven, human activity is directly responsible

The Met Office study (the service weather report English National), published in Journal of Climate, is the first to highlight the influence of human activity on rainfall extremes in Europe. Scientists compared different climate scenarios, with and without human influence. the Met Office went back to 1850 to compare the evolution of the climate in the Mediterranean and the rest of Europe.

Increasingly extreme rains in the north

If the IPCC reports had already pointed out the effect of global warming on the precipitation at the global level, the case of Europe had not yet been analyzed with precision. With each degree of warming gained, the process of evaporation of water is stronger and increases precipitation by 7%. This is a global observation, but this increase in precipitation is not uniform throughout the world: areas that are already humid, such as northern Europe, are becoming even wetter and subject to episodes of extreme rainfall, and therefore at risk of flooding. Like the historic floods which caused the death of nearly 300 people in Germany and Belgium in July 2021: it is always difficult to attribute a single event, however violent, to global warming, but the rise in temperatures multiplies the probability that this type of extreme phenomenon to occur. However, dry and arid areas, such as the Mediterranean basin, face an increasingly dry climate, leading to persistent drought.

The cooling role of aerosols

With their climate models, the researchers simulated a situation in which human influence does not exist. Then another situation in which the evolution of the European climate is solely influenced by aerosolsand a final situation in which the climate of Europe is influenced by aerosols and greenhouse gas. The results were very clear: greenhouse gas are the main factor influencing climate change in Europe. But the simulations also showed that the aerosols attenuated this influence, with a cooling effect. Remember that aerosols are polluting particles harmful to the environment and our health: these particles can be of natural origin (forest fires, volcanic ash, etc.) and artificial (combustion from coalfrom fuel oil, etc). Some aerosols have a cooling effect while others contribute to global warming.

Extremes that are accentuated especially in winter

The climate models used study the role of different causes, natural and human. The results show that the emissions due to human activities accentuate trends, with drier seasons in the Mediterranean and wetter on the rest of the European continent. These contrasts accentuate in winter and are less marked in summer, when the drought is more generalized. The only exception in summer is a marked increase in rainfall in Scandinavia. Winter precipitation is directly influenced by anthropogenic warming (i.e. resulting from human activity): the frequency of extreme precipitation is increasing everywhere except in the Mediterranean basin, an area in which the rains are increasingly rare. The increase in precipitation in northern Europe would in fact be linked to a Jet-Stream which would circulate further south, in connection with the melting ice-creams.

The authors of the study specify that the trend towards a drier climate in the Mediterranean and wetter elsewhere will continue to worsen, but not in a progressive and linear way: climate simulations have shown that the evolution takes place in a brutal, not with a continuous rise, but with a cascade of violent events and sudden. With this observation and these projections, the authors of the study specify that our activities must adapt, in particular theagriculture of the Mediterranean basin, and that the other regions of Europe must prepare for an increasingly present risk of flooding.