Scientists want to put "speed bumps" in a hurricane alley to slow down storms


TThe benefits of wind energy are well known. The wind is clean, abundant and renewable. The installation of a large number of turbines could help our high-carbon civilization to break free from its dependence on fossil fuels. New research suggests that someday, there could be another major benefit: massive wind turbine installations could mitigate the flood when powerful hurricanes cause devastating amounts of rain on the ground. During recent storms like Harvey and Florence, which resulted in historic rainfall levels, this could have meant less floods and fewer destructions and fewer deaths.

"Offshore wind farms could certainly be a potential tool for weakening hurricanes and reducing their damage," says Cristina Archer, a professor at the University of Delaware's College of Earth, Ocean and Environment, who has conducted a recent study published in the newspaper. . Letters of research on the environment describing the impact of offshore turbines on rainfalls. "And they pay for themselves, in the end, that's why I'm excited about it."

Climate change has resulted in larger and more intense hurricanes in recent years. The evaporation of seawater feeds hurricanes, the strength of which depends on how quickly the water can evaporate from the ocean. When seawater evaporates, it transfers heat from the ocean to the atmosphere, converting it into wind energy, creating increasingly powerful winds. As the water temperature increases, the rate of evaporation also increases, as well as the wind. The warmer the ocean, the faster the evaporation. And climate change is heating up the oceans at a worrying pace.

In previous research, Archer had demonstrated that offshore wind farms absorb the kinetic energy of hurricanes, reducing the effects of wind and storm surges. His latest study suggests that turbines could also reduce precipitation for coastal sites located downstream of a wind farm – when they are deployed in very large numbers. "The motivation for this new study was fundamentally Harvey," says Archer. "He dumped an incredible amount of rain, and that's the rain that caused the flood in the Houston area."

To imagine what happens when a hurricane meets a wind turbine – and how wind turbines can reduce precipitation – it is important to understand the two important factors that influence precipitation, convergence, and divergence. Strong hurricane winds slow down when they collide with wind turbines and rise because they have no other place to go. This brings more moisture into the atmosphere, increasing precipitation. That's the convergence.

The divergence is the opposite. it causes a downward movement, attracting a drier air that moves downwards, which suppresses precipitation.

"Think of convergence, for example when there is traffic on a highway and everyone goes fast, then all of a sudden there is an accident and everyone slows down," says Archer. "You get a convergence of cars that saves … it's upstream convergence of offshore wind farms. The discrepancy is similar to what happens when cars end up overtaking the accident and everyone speeds up. "

Convergence and divergence naturally occur in many situations. "For example, wherever we have a low pressure center, associated with storms at mid-latitudes, the surface winds usually converge towards it," says Archer. "Conversely, everywhere we have a center of high pressure, as in clear and hot weather, the winds on the surface diverge. When you change the land use, for example from one ocean to another or from one forest to another, this causes a change in the winds – a slowdown in the Ocean to the ground or a forest acceleration to the grass – and you get a convergence and a divergence, respectively. "

On a wind farm, the wind speed slows down "because that's what the turbines do," she says. "They extract the kinetic energy of the wind, which is why the wind behind them, downstream of each turbine, is lower than upstream." Put more and more wind turbines in a big farm and you can imagine that you would start to create a convergence ahead of the farm, before the winds reach the first turbines, then to a divergence after that after the farm, where the winds are accelerating again.

Therefore, for there to be rainfall, there has to be an upward movement to bring the moisture-rich air near the surface into the atmosphere, where it is condense and cause rain. "To get up close to the surface, you have to have convergence," she says. Then, "to suppress precipitation, you need a downward movement, which happens when you have a divergence on the surface. Obviously, you also need a high humidity environment to start with. If you have a convergence in the desert, whatever its strength, there will be no precipitation, because it is too dry. "

This is why scientists have been studying the impact of offshore wind farms, rather than onshore, when hurricanes form above water and dissipate quickly once they reach land. "There is a lot of humidity [offshore]it was more likely that we would see an effect, "she says. "We looked at hurricanes because they last long enough for convergence and divergence patterns to form and persist. If you think about it, a hurricane lasts for days and causes strong and constant winds in the same direction – from ocean to land.

A current disadvantage is that turbines are often turned off in high winds. Archer said their computer simulations took into account the "cut" wind speed, which is currently 76 miles to the hour for Enercon 126, a model of German offshore wind. However, manufacturers are currently developing new turbines that will withstand even stronger winds, such as hurricanes and typhoons, and these should be on the market by 2020, she added.

Scientists used digital computer simulations covering the Texas and Louisiana coasts, examining what could have happened in the presence of offshore wind farms during Harvey's course. They examined a large number of turbines, on areas of different sizes and in various configurations.

"As the air reaches the mainland, it has been evacuated by a lot of moisture," says Archer. "We got a 30% reduction in precipitation with the Harvey simulations. This means that potentially, if you have offshore turbine batteries in an area where there are hurricanes, you will probably see a reduction in precipitation inland. "

The study used hypothetical turbines ranging from a zero turbines control case to a high of 74,619, a number currently unrealistic for the United States, she said. Unlike Europe, where there are more than 100 offshore wind turbines, the United States has only five, which are part of the country's first and only offshore wind farm, located on Block Island, off the coast. Rhode Island coast.

The largest configuration had 74,000 people and the smallest 22,000, she said. "So these are high numbers," she says. "In comparison, there are about 300,000 turbines in the world today."

Although she thinks the more turbines there are, the better, the scientists found that using fewer turbines or placing them on a smaller surface had positive effects. "For example, you do not need to [turbines covering a large area]Said Archer. You can get pretty much the same benefit with [a smaller layout] placed "intelligently" for Houston. "

With 33,363 turbines in a medium-sized area, they recorded a 15% reduction in the Houston metropolitan area. With 28,197 turbines on the small [area]she says that they saw a 10 percent reduction. "We're getting bigger discounts in other places, but we've focused on totals for metro Houston."

For now, researchers can not predict the optimal number of wind turbines needed, although "the most [offshore] the wind farms you have, the more they will impact a hurricane, "she says. "By the time a hurricane has touched down, these turbine batteries have been running for days and days, extracting energy and moisture from the storm. As a result, the storm will be weaker. Literally."

She noted that communities can build artificial dikes or barrier islands to protect themselves against storm surges. But these will not protect against the rain. "The costs are high and they only serve one purpose," she says. "An alternative is to build offshore wind farms, which [ultimately] Pay for yourself, generate clean, renewable energy and, best of all, protect against hurricanes, including rain and storm surges. "

Marlene Cimons writes for Nexus Media, an outsourced newswire covering climate, energy, politics, art, and culture.