Cyclone Chido has become the worst storm to impact the French overseas territory of Mayotte in the Indian Ocean in 90 years.

Here is more about the destruction caused by Chido and what may come next:

What is Cyclone Chido?

Chido developed from a tropical depression in the southeastern Indian Ocean basin from December 7 to 8.

A tropical depression is an area of low pressure over an ocean accompanied by circular wind flow produced by thunderstorms. Tropical depressions have maximum sustained wind speeds of 61km/h (38mph) or less.

A tropical depression can intensify and become a tropical storm if wind speeds are from 62km/h (39mph) to 119km/h (74mph). Anything above that is considered a tropical cyclone.

The terminology can be slightly confusing. Tropical cyclones are called hurricanes when they occur in the Atlantic Ocean, Gulf of Mexico, Caribbean Sea and northeastern Pacific Ocean and are called typhoons when they occur in the western Pacific Ocean. And when they occur in the South Pacific and the Indian Ocean, they are referred to as cyclones.

Chido intensified into a cyclone and hit Mayotte, an archipelago home to 320,000 people off the east coast of Africa. While Mayotte lies in the Indian Ocean, it is an overseas department of France and is directly ruled from Paris. However, it is France’s poorest region, and an estimated third of the population live in shanty towns.

The cyclone has also impacted surrounding nations in southeastern Africa, bringing heavy rainfall and damaging houses in Madagascar, Mozambique and the Comoros Islands before weakening.

According to an early estimate, at least three people have died in Mozambique, local officials told the AFP news agency.

When and where did Chido make landfall?

Chido hit Mayotte on Saturday morning with wind speeds exceeding 220km/h (137mph).

It made landfall as a tropical storm in Mozambique on Sunday morning.

Chido was incredibly powerful. It was equivalent to a Category 4 hurricane at the time of landfall in Mayotte, making it the second strongest type of storm on the Saffir-Simpson scale.

According to the National Hurricane Center in the United States, Category 4 storms, which have wind speeds ranging from 209km/h to 251km/h (130mph to 156mph) cause “catastrophic damage”. They can destroy well-built homes, uproot trees and down power poles, leading to power outages.

How many people have been killed by Chido in Mayotte?

According to France’s Interministerial Crisis Management Operational Centre (COGIC), the official death toll in Mayotte as a result of Chido is 19 people.

However, it is feared that Chido has actually killed hundreds of people.

The French Ministry of Interior has said “it will be difficult to account for all victims” and a conclusive number of those affected by Chido has not been determined yet.

Determining the death toll could take “days and days”, Interior Minister Bruno Retailleau told French media. Retailleau arrived in Mayotte’s capital, Mamoudzou, on Monday.

France has sent medical and military personnel to Mayotte on ships and military aircraft.

Rescue workers, including reinforcements from France, are digging through debris to try to find survivors of the cyclone.

“I think there will certainly be several hundreds. Maybe we will reach a thousand, even several thousands,” senior local French official Francois-Xavier Bieuville told the local media channel Mayotte la 1ere on Sunday.

The uncertainty is partly due to the large number of undocumented migrants in Mayotte – more than 100,000, according to French authorities. Additionally, a French Interior Ministry official said determining the death toll would be complicated because “Mayotte is a Muslim land where the dead are buried within 24 hours.”

Many of Mayotte’s migrants come from the neighbouring Comoros Islands and East African countries such as Somalia. They are attracted by better economic opportunities that come with Mayotte’s status as a department of France.

How badly damaged is Mayotte’s infrastructure?

According to COGIC, 830 people have been injured, including 24 with severe injuries. Additionally, 100,000 people have been moved to 70 emergency shelters.

Critical infrastructure in Mayotte has been damaged, including roads, water treatment plants and electrical transmission lines.

“The health system is seriously affected, and access to care has been seriously degraded,” outgoing French Health Minister Genevieve Darrieussecq said on Sunday.

The control tower of Mayotte’s main airport, Dzaoudzi–Pamandzi, also sustained damage. This has made rescue operations difficult because only military aircraft can now fly into Mayotte.

According to the internet monitoring group NetBlocks on Monday, Mayotte has been offline almost entirely for more than 36 hours. COGIC reported 15,000 people have experienced power outages.

Impoverished communities have been hit hardest by the cyclone. Mayotte’s shanty towns, where most homes are built with sheet metal, were not constructed to withstand the power of a cyclone, and many of the dead are believed to have been living in these areas.

Damage to infrastructure has left some communities in Mayotte without food and water since Saturday, said Salama Ramia, a senator representing Mayotte in the French Senate.

Mayotte is the poorest French overseas territory and is also believed to be the poorest European Union territory. Three out of four people in the island nation live below the poverty line.

For years, Mayotte has struggled with water shortages, drought and underinvestment.

Where is Chido now?

As of 09:00 GMT on Monday, Chido had weakened to a remnant low, or a post-tropical cyclone, slightly south of the Balaka township in Malawi. It had a speed of 45km/h (28mph).

What’s next?

According to ReliefWeb, Chido is expected to dissipate near Zimbabwe on Tuesday.

Cyclones typically form in the southwestern Indian Ocean from November to April. An average of 12 cyclones form per year.

In 2019, Cyclone Idai killed more than 1,300 people in countries including Malawi, Mozambique and Zimbabwe. In 2023, Cyclone Freddy caused storms for a month, killing more than 1,000 people in East Africa. Freddy remained a tropical cyclone for 36 days, and the World Meteorological Organization declared it the longest lasting tropical cyclone on record.

Scientists warn that cyclones are becoming more powerful because of climate change and warming bodies of water.

“The Indian Ocean is warming at a fast rate, and it is going to warm much more faster in the near future,” Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology, told Al Jazeera. He based those findings on research he conducted and published in 2022.

“In fact, the waters where Cyclone Chido developed were 1 to 2 degrees [Celsius – 1.8 to 3.6 degrees Fahrenheit] warmer than usual,” Koll said.

Koll said that to prevent destruction such as that caused by a cyclone like Chido, cyclones need to be monitored better. He added that governments need to fund agencies that monitor the storms. Better monitoring can lead to timely warnings for residents living in areas where a cyclone is predicted to have an impact, according to the European Organisation for the Exploitation of Meteorological Satellites.

Additionally, Koll said, countries need to “disaster proof” coastal cities and towns, ensuring that infrastructure is prepared so damage by cyclones is minimised and lives and livelihoods are saved. Coastal cities in particular are vulnerable to storm surges and flooding.