(CNN) Hurricanes and tropical storms, known as tropical cyclones, are moving slower around the planet, according to a new study from National Oceanic and Atmospheric Administration scientist James Kossin.

The study, released Wednesday in the scientific journal Nature , showed a 10% decrease in forward speed globally between 1949 and 2016, though there is some variation among ocean basins.

Kossin, who is also with the National Centers for Environmental Information, found a 20% to 30% slowdown over land areas affected by North Atlantic and North Pacific tropical cyclones, respectively.

Slower-moving storms mean greater rainfall totals, as seen with Hurricane Harvey in Texas last year.

"These trends are almost certainly increasing local rainfall totals and freshwater flooding," Kossin said, "which is associated with very high mortality risk."

According to NOAA, inland flooding accounts for around 25% of hurricane-related deaths each year.

Although more rainfall is the most direct consequence of slower-moving storms, other impacts can be enhanced as well.

Water flows down Interstate 10 in Houston amid record flooding from Hurricane Harvey.

"Long-duration or slower-moving storms, even when weaker, can have exacerbated impacts through prolonged wind exposure [in addition to] flooding," according to Colin Zarzycki, a project scientist with the National Center for Atmospheric Research who was not involved with the study.

According to the study, which looked at each ocean basin where tropical systems form, a slowdown in the movement of the storms has been observed in every basin except the Northern Indian Ocean.

Tropical cyclones have slowed more in the Northern Hemisphere, which is significant because that is where a majority of storms occur each year.

The western North Pacific basin, where the strongest systems are referred to as typhoons and super typhoons, sees the most storms annually and has seen the most slowing, at 20%.

Is Hurricane Harvey a preview?

The impacts of slower-moving storms are devastating.

Hurricane Harvey, which progressed at a walking pace over eastern Texas after making landfall in late August, dumped rain in amounts that were a record from a tropical system in the United States: more than 60 inches.

Photos: Hurricane Harvey slams Texas Downtown Houston is seen behind the flooded Buffalo Bayou a few days after Hurricane Harvey came ashore in August 2017. The Category 4 storm caused historic flooding. It set a record for the most rainfall from a tropical cyclone in the continental United States, with 51 inches of rain recorded in areas of Texas. An estimated 27 trillion gallons of water fell over Texas and Louisiana during a six-day period. Hide Caption 1 of 22 Photos: Hurricane Harvey slams Texas NASA astronaut Jack Fischer photographed Hurricane Harvey from the International Space Station. Hide Caption 2 of 22 Photos: Hurricane Harvey slams Texas Steve Culver comforts his dog Otis in the hurricane aftermath. Harvey destroyed most of his home in Rockport while he and his wife were there. Hide Caption 3 of 22 Photos: Hurricane Harvey slams Texas Houston police officer Daryl Hudeck carries Catherine Pham and her 13-month-old son, Aiden, after rescuing them from floodwaters. Hide Caption 4 of 22 Photos: Hurricane Harvey slams Texas A damaged home is seen in the Key Allegro neighborhood of Rockport. Hide Caption 5 of 22 Photos: Hurricane Harvey slams Texas A car is submerged by floodwaters on a freeway near downtown Houston. Hide Caption 6 of 22 Photos: Hurricane Harvey slams Texas Melani Zurawski cries while inspecting her home in Port Aransas, Texas. Hide Caption 7 of 22 Photos: Hurricane Harvey slams Texas A graveyard is flooded in Pearland, Texas. Hide Caption 8 of 22 Photos: Hurricane Harvey slams Texas Soldiers with the National Guard patrol Rockport, looking for residents trapped in their homes. Hide Caption 9 of 22 Photos: Hurricane Harvey slams Texas Evacuees are loaded onto a truck in Houston. Hide Caption 10 of 22 Photos: Hurricane Harvey slams Texas People push a stalled pickup through a flooded street in Houston. Hide Caption 11 of 22 Photos: Hurricane Harvey slams Texas Rockport residents return to their destroyed home. Hide Caption 12 of 22 Photos: Hurricane Harvey slams Texas Rescue boats fill Tidwell Road in Houston as they help flood victims evacuate the area. Hide Caption 13 of 22 Photos: Hurricane Harvey slams Texas People wait to be rescued from their flooded home in Houston. Hide Caption 14 of 22 Photos: Hurricane Harvey slams Texas Volunteers in Dallas organize items donated for hurricane victims. Hide Caption 15 of 22 Photos: Hurricane Harvey slams Texas When Harvey slammed the Texas coast and flooded much of Houston, volunteers sprang into action. Some came from as far away as the Florida Everglades, boats in tow, ready to rescue people trapped in their homes. Hide Caption 16 of 22 Photos: Hurricane Harvey slams Texas Larry Koser Jr. and his son Matthew look for important papers and heirlooms inside a flooded home in Houston. Hide Caption 17 of 22 Photos: Hurricane Harvey slams Texas Members of the National Guard rest at a furniture store in Richmond, Texas. Hide Caption 18 of 22 Photos: Hurricane Harvey slams Texas Volunteer rescue workers help a woman from her flooded home in Port Arthur, Texas. Hide Caption 19 of 22 Photos: Hurricane Harvey slams Texas This aerial photo shows flooded residential neighborhoods in Houston. Hide Caption 20 of 22 Photos: Hurricane Harvey slams Texas Tammy Dominguez and her husband, Christopher, sleep on cots at the George R. Brown Convention Center, where thousands of people were taking shelter in Houston. Hide Caption 21 of 22 Photos: Hurricane Harvey slams Texas An elderly patient waits to be rescued from the Gulf Health Care Center in Port Arthur. The facility was evacuated with the help of first responders and volunteers. Hide Caption 22 of 22

The storm affected 4.7 million people in and around Houston directly or indirectly during the flood and resulted in 68 fatalities, the largest number from a landfalling hurricane in Texas since 1919, according to a report released Wednesday by the Harris County Flood Control District.

In addition to slower atmospheric circulations possibly causing the storms to move slower, the amount of rainfall that the storms are able to dump is increasing as global temperatures climb.

Warmer air is able to hold more water vapor through a process called the Clausius-Clapeyron relationship, which shows that the water-holding capability of air increases about 7% with each degree Celsius of warming.

According to Kossin's study, combining the additional water vapor available in the atmosphere from 1 degree Celsius of warming -- essentially where we are now -- with a 10% slowdown from tropical cyclones that he observed would double the local rainfall and flooding impacts.

If Harvey is any indication of what hurricanes will look like in the future , this will create a considerable strain on countries' ability to respond financially to storms.

Harvey was the second costliest storm on record , behind Hurricane Katrina, totaling $125 billion in damage -- of which about two-thirds were uninsured flood losses.

Why are storms slowing down?

Although this study did not investigate directly what is causing the tropical cyclones to slow, it presents a hypothesis that was the basis for the research.

There is considerable evidence that global summertime circulation patterns in the atmosphere are slowing as a result of global warming.

"Storms should be responding to changes in the whole global wind pattern, since they are mostly just carried along in the flow," Kossin said.

Therefore, it would make sense that if the flow around the hurricanes and typhoons is moving slowly, the storms will also be moving slower, which Kossin believes is what he is observing in the data.

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But there are probably more variables at play than a warmer climate putting the brakes on tropical cyclones.

"It is far from clear that global climate change has anything to do with the changes being identified," said Kevin Trenberth, a senior climate scientist with the National Center for Atmospheric Research.

Several major natural climate variations occur over long periods, such as the Pacific Decadal Oscillation, which is similar to the El Niño/La Niña oscillation that can significantly alter global weather but operates on much longer time scales (hence "decadal," whereas El Niño/La Niña alternate from year to year).

Trenberth points out that this study did not account for these natural cycles, which he said could be behind much of the observed trend.

Kossin admits that there are probably both natural and manmade factors influencing the slowing of storms and recommends further studies using climate models to determine how much greenhouse gas emissions are responsible for affecting the storms' speeds.

"What we're seeing almost certainly reflects both natural and human-caused changes," Kossin said. "We'll need more formal attribution studies to disentangle these factors."