Hours of rain: Ian’s second hit hard by climate change | Currently

Hurricane Ian brought more than 10 percent of the additional rain to Florida as a result of global warming. American scientists think so based on research in the hurricane season two years ago. This increase in precipitation has a double cause, and it is getting stronger as the climate warms.

If a Category 5 hurricane approaches, you can go up your windows in the hope that your roof can withstand winds of more than 250 kilometers per hour.

But however brutal that natural force may be, the biggest cause of hurricane damage has yet to follow: water. Because of the extremely low atmospheric pressure, Ian caused a local tsunami of 3.6 meters on the west coast of Florida. On land, flooding was followed by torrential rain that carried the remainder of the hurricane from the Gulf of Mexico to Canada.

A colder hurricane brings less rain

The rainfall in the wake of Ian is stronger than if a hurricane of equal strength passed over the 1900 climate. This is what researchers from three different US universities concluded from an analysis of the 2020 hurricane season. The research was published in April. published in trade magazine Nature Communications.

When they tried to simulate those hurricanes with climate models, they found that the peak rainfall in particular during the storm’s passage is much higher in the current warm climate. In the southern United States, hurricanes now bring 10 percent more rain in the first three hours than they did in the original, cooler climate.

According to researchers in the United States, crossing the remains of hurricanes also brings more rain these days. Total precipitation for the first three days increased by about 5 percent. This could be the straw that breaks the camel’s back: With more rainfall, water damage increases disproportionately.

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Double climate effect: more water vapor and air rising faster

The main reason is that warmer air can hold more water vapor: 7 percent per degree. This does not provide a conclusive explanation, the researchers say, because the sea water where the Atlantic hurricanes are approaching has warmed only 0.8 degrees. This is lower than the global average, and could only explain a 5 percent increase in total precipitation for three days.

The reason for the increase in precipitation twice as fast in the first three hours is the increase in air currents in hurricanes. As the warm, moist air rises, a very large amount of water condenses, releasing energy, causing the airflow to rise faster. In a warmer climate, this also results in almost twice as much precipitation – which in this case explains the other 5 percent increase in precipitation.

Hurricane maximum wind speed also increasing by climate change. Not the number of hurricanes.

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