The rate at which hurricane are moving has slowed down globally over the last seven decades, especially in coastal areas, show work done in the United States. This average slowdown of about 10% of the translational speed of tropical cyclones means more rain and, potentially, more floods, hence more damage in populated areas. This drop in speed occurred during a period when the planet warmed by 0.5 degrees.
To reach this conclusion, scientist James Kossin and his colleagues at the University of Wisconsin in Madison analyzed meteorological data for hurricanes from 1949 to 2016. Their results show that a storm lingers on average in a given area over a longer period, such as Hurricane Harvey, which stagnated over eastern Texas for nearly a week in August 2017.
All the reasons for this slowdown are not understood, but climate change is believed to be part of the problem. “As the Earth’s atmosphere warms, atmospheric circulation changes,” says James Kossin. His work suggests, he says, that global warming is causing a general loss of speed in the summer tropical circulation. These changes are uneven and vary by region and time of year. The observed hurricane slowdown would be 20% and 30% respectively above the hurricane areas of the North Atlantic and Northwest Pacific hurricanes, and 19% above the Australian territory.
It should also be mentioned that warming also increases the amount of water vapor present in the atmosphere, which can lead to increased precipitation.
According to Dr. Kossin, it is essential to continue research on the effect of climate change on hurricanes to understand global risk trends. However, these studies do not provide an exact measure of the influence of the climate. They also cannot predict the slowdown rate in the coming years depending on the warming that will continue.
This work also underscores the importance of global atmospheric circulation of precipitation at the regional scale caused by tropical storms. These storms tend to “follow the current” where they are, which means that their direction and the speed at which they move are guided by the winds of the immediate environment. As a result, any change in tropical wind circulation could likely affect the speed of hurricane movement.
The details of this work are published in the journal Scientific Reports.