Hurricanes are complex and difficult to predict. With the rarity of these events and the small amount of historical data, it is difficult to say that climate change is worsening the impact. However, we can say with a great deal of certainty that it is likely.
Not to be confused with a tropical storm with wind speeds between 39 mph and 74 mph.
A hurricane / typhoon / tropical cyclone is a rotating low-pressure weather system that generates high-powered circular winds of over 74 mph (Category 1) and reaching 157+ mph (Category 5).
How does a hurricane form?
Ø Begins as areas of tropical activity in tropical regions, called tropical waves
Ø As area becomes more organised, the moisture condenses and clouds are forming
Ø This process of condensation releases heat into the air
Ø This heat causes the air to rise and expand which decreases air pressure
Ø Area in surounding area starts to flow into the tropical wave (Air moves from areas of higher pressure to lower pressure)
Ø The air also begins to become warmer and condense, creating a strengthening pattern
Ø As more air begins to flow, the storm begins to grow stronger, the system of clouds and wind spins and grows
Ø It will begin to rotate due to the Earth’s rotation, (Counterclockwise North, Clockwise South)
Ø If conditions, remain suitable, the storm becomes stronger, forming a hurricane
Ø As the storm roates faster, an eye forms in the centre, an area of low pressure
Ø Higher pressure air from above flows down into the eye
So how does climate change increase the intensity?
There’s a well established physical law, the Clausius-Clapeyron equation that says a hotter atmosphere holds more moisture. For every degree celcius in warming, the atmosphere can hold 7% more water, which tends to make rainfall events more extreme. Therefore global warming caused by increasing greenhouse gases in the atmosphere from burning fossil fuels is raising temperature globally.
In addition, hurricanes use the energy from warm tropical oceans to build up energy and sustain it before making landfall. Therefore a warmer ocean means that there is increasing evaporation and more water vapour rising into the atmosphere, strengthening the hurricane which adds to the moisture and wind speeds, therefore increasing the intensity and rainfall.
How was this shown in Hurricane Harvey?
Hurricane Harvey, a Category 4 storm made landfall on August 25th 2017
The waters of the Gulf of Mexico are about 1.5 degrees warmer than the period from 1980-2010.
A study in the Geophysical Research Letters (GRL) finds that Hurricane Harvey’s seven day rainfall total potentially increased by at least 19% up to 38% compared to a similar storm in the mid-20th century.
In this study. Researchers used a statistical model based on historical climate data to separate how much of the extreme rainfall from Hurricane Harvey was due to natural influences and how much was from human influences. It estimated the amount of precipitation that would have fallen in an event of the same magnitude using 1950s greenhouse gas levels.
The study authors expected a 6% increase in rainfall due to warming in the Gulf of Mexico.
Another study from the Environmental Research Letters (ERL) finds that climate change made the record three-day rainfall that fell over Houston roughly three times more likely and 15% more intense than a similar storm in the early 1900s.
Overall, the chances of seeing a rainfall event as intense as Harvey have roughly tripled - somewhere between 1.5 and five times more likely - since the 1900s and the intensity of such an event has increased between 8 percent and 19 percent, according to the new study by researchers with World Weather Attribution.
A hurricane is just a storm, it’s not the disaster.
The impacts on Houston was considered a disaster due to the damage the hurricane inflicted. What likely increased the severity of this event is due to the fact that the Houston population has increased by 40% since 1990, with many people too poor to afford insurance or evacuate.
Climate is certainly increasing the effects of hurricanes. Not only do warmer oceans create stronger winds, as it rises to the atmosphere it can also hold more moisture forming greater clouds and increasing rainfall.
The effects in the future are likely to become worse as climate change continues to happen. Mitigation via regulations and adaptations such as defences and repairing buildings are key to the safety of civilian populations.