Heavy downpours in Paris flooded subway stations in the French capital Tuesday. Some places received more rain in one hour than the average for one month. The French meteorological service warned that much of the country’s south could face storms.
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The extreme rainfall comes as nearly half of Europe is in a drought that some scientists say may be the worst in 500 years. It has been accompanied by unprecedented heat waves and wildfires, breaking temperature records in the past two months and leading to the deaths of at least 1,600 people.
Scientists are careful not to link specific extreme weather events to the climate crisis; only extended research will make that possible. But they note that while not every extreme event is necessarily linked to the crisis, it has been proved that the crisis exacerbates many extreme weather events.
It’s already clear why an increasing number of extreme weather events are taking place concurrently. Researchers from the Weizmann Institute of Science in Rehovot and the universities of Haifa and Tel Aviv explain that extreme heat and extreme rainstorms are not contradictory but frequently affected by each other. All the experts stressed that in an era of extreme warming caused by the burning of fossil fuels, such events will be more common.
Prof. Emeritus Haim Kutiel of the University of Haifa explains: “Intense rain for a short time is created in conditions of extreme instability” usually resulting from a large temperature difference between the warm surface of the Earth and the air layers above it. “After a long period of very high temperatures, as we’ve seen in recent weeks throughout Europe, the penetration of relatively cooler, more humid air is enough to cause great instability and intense rainstorms.”
Prof. Hadas Saaroni of Tel Aviv University says: “There are various dynamic factors leading to a rise in extreme events directly associated with warming. Among others, warming causes more evaporation and latent heat, which is the storms’ energy. And this is why it causes more extreme storms. While one region suffers more from heat waves, another can be struck by strong storms at the same time and vice versa, so that every area can suffer from radicalization reflected in heat waves or intense storms and floods.”
Rei Chemke of the Weizmann Institute says: “Extreme events become stronger under the rise of greenhouse gasses, both due to the rise in temperature and the changes in the atmospheric circulation. The temperature rise enables the existence of more water vapor in the atmosphere, which enables heavier downpours, but also more dryness events due to the decrease in upward moisture flux from the earth to the atmosphere.”
“Western Europe is impacted by the moisture and heat flux the winds bring from the Atlantic Ocean. The winds’ weakening in the summer in recent years decreases the flux of cold, humid air from the sea to the land, which increases the chance of heat and dryness events in these areas,” he says.
Will flooding like that in the Paris metro increase in the warming world? Absolutely, Kutiel says. “When it rains on a mostly built-up urban or paved area that water cannot penetrate, it causes flooding such as occurred this week in Paris, a few weeks ago in Sydney, Australia and last year in several German and Belgian cities. No urban drainage system in the world can cope with such quantities of water in a short time period. The upward warming trend in the coming years predicts that such events could become routine occurrences.”
Saaroni stresses the effect of humans on these events. “A significant factor that makes it hard for us to deal with climate changes is the direct influence of human beings on changing the landscape. That is, the way we build cities, streets and roads.”