The precipitation and temperatures are the two main parameters that define our weather report and our climate. How do temperature extremes influence the amount of precipitation in the Northern Hemisphere during summer and winter? This is the question that this new study from the Institute of Atmospheric and Climatic Sciences in Zurich.
If the experts of IPCC agree on a raise episodes of torrential rainfall, and therefore flooding, over the next few years due to the global warmingthe conclusions of the Zurich Institute are more precise: the evolution of rainfall will be different from one region of the globe to another and from one season to the other. Scientists have studied climatic variations in several areas in Europe, the Mediterranean and North America.
More rain in cool summers and mild winters in Europe
The study demonstrates the complex relationship between the level of temperatures recorded at 2 meters and the amount of precipitation received, and thus highlights light regional differences. Precipitation is not necessarily more intense during warmer than average weather, researchers have proven that, in certain regions, precipitation is stronger during cold weather.
In the Mediterranean, the strongest rains fall on the warmest days of winter, but in the Rocky Mountains Americans, precipitation is greater on the coldest days of the same season. Precipitation is heaviest in summer in high latitudes, and heaviest in winter in continental climates.
The difference is related to the types of weather systems that form in these regions: in winter, depressions are the dominant weather system, while in summer heavy precipitation comes more from atmospheric rivers. In the departments of the French Mediterranean arc, the observation is very clear: the rains are much more intense during mild winters, and much less intense during hot summers. In England, the abnormally mild and wet winter of 2013-2014 was accompanied by several extratropical cyclones, generators torrential rains.
Better predict extreme weather events
Overall, the study showed that the rainiest winters incentral Europe occur against the backdrop of higher than average temperatures, while the wettest winters in the United States occur against the backdrop of temperatures below the seasonal averages. However, in Europe as in the United States, the wettest summers occur during an abnormally cool summer season.
Behind this very general observation, regional climatic differences obviously exist, particularly between the north, center and east of the United States, but also between northern Europe and the Mediterranean arc. But the episodes of intense precipitation are ultimately always correlated with extremes, hot or cold.
The objective of the study is thus to better predict the evolution of precipitation in the various countries: a factor which obviously has significant consequences on the economy and the environment, all the more so in the context of global warming which is expected to accentuate temperature extremes over the next few years.
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