A new study conducted by the National Oceanic and Atmospheric Administration (NOAA) has found that hurricanes and tropical storms, also known as tropical cyclones, have seen a striking slowdown in their speed of movement around the planet over the past 65 years. The study, published in the journal Nature, found a 10 percent slowdown in storm speed between 1949 and 2016.
The study looked at each ocean basin where tropical systems form and found a slowdown in the movement of the storms in every basin except the Northern Indian Ocean. The slowdown in the storms’ travel over land was some cases even more pronounced than it was over the oceans. The study found a 20 percent to 30 percent slowdown over land areas affected by North Atlantic and North Pacific tropical cyclones, respectively.
Jim Kossin, a scientist with NOAA and the study’s author, says that the finding suggests rising rainfall and storm-surge risks. Slower-moving storms rain more over a given area, cause more damage with their winds and increase storm surge as they approach shorelines. According to NOAA, inland flooding accounts for more than 50 percent of hurricane-related deaths each year. Kossin said, “Inland flooding, freshwater flooding, is taking over as the key mortality risk now associated with these storms. There’s been a sea change there in terms of what’s dangerous.”
Hurricane Harvey, which hit Texas last year, is a good example of this theory in practice. The storm’s catastrophic rains were enabled by its slow pace through the Houston area after making landfall in late August. Hurricane Harvey dumped more than 60 inches of rain on the area, affecting 4.7 million people in and around the Houston area and resulting in 68 fatalities.
If Harvey is what hurricanes will look like in the future, countries’ ability to respond financially to storms will be greatly impacted. However, it is not clear just how much of the change Kossin found is attributable to human-induced climate change. There may be a natural cycle to the climate system that could be affecting the storms which has little or nothing to do with global warming. Further research on the matter is needed.