Lessons for Hong Kong in the way typhoon Haiyan wreaked destruction
Climate change may boost super typhoons, and the city has been lucky in recent years to escape tsunami-like storm surges
In the aftermath of Super Typhoon Haiyan devastating large swathes of the Philippines, the news media have linked the storm's ferocity to climate change. So did Yeb Sano, lead negotiator for the Philippines at the United Nations climate talks that are currently under way in Poland. "What my country is going through as a result of this extreme climate event is madness. The climate crisis is madness," Sano said in an emotional speech three days after the storm hit.
Yet madness though the climate crisis may be, it is hard to link Haiyan to climate change. Indeed, it is not even straightforward determining whether it truly was the strongest storm ever to make landfall.
The latter claim is largely based on the US Navy's Joint Typhoon Warning Centre estimating that just before Haiyan made landfall, its maximum sustained winds were 314 km/h. The figure was derived from satellite observations, and is marginally higher than the previous record holder, Hurricane Camille, which came ashore in the southeastern US in 1969.
By another measure of strength - air pressure - Haiyan might rank as the 12th strongest tropical cyclone on record, according to Dr Jeff Masters, cofounder of the website Weather Underground. But it is, however, important to note that it was close to the theoretical upper limit for tropical cyclones.
Masters wrote that Haiyan was powered by unusually warm sub-surface waters east of the Philippines - which were four to five degrees Celsius above average last month. One factor in causing this warmth may have been relatively strong trade winds in recent years. But also, the anomalous warmth is consistent with climate change.
A paper submitted to Geophysical Research Letters this spring analysed the warming west Pacific waters. In the main development region for typhoons, the tropical heat potential had become 10 per cent higher than in the 1990s. This had made the region even more favourable for typhoon and super typhoon intensification.
Professor Johnny Chan Chung-leung, dean of the school of energy and environment at the City University of Hong Kong, has cautioned that warming Pacific Ocean temperatures need not necessarily result in more typhoons, as these also require stronger atmospheric circulations. Indeed, for 1960 to 2005 he found no increase in frequency of Pacific typhoons.
There is, however, some evidence that the strongest typhoons are becoming more intense, such as an analysis of 25 years of satellite data that was published in Nature in 2008. And a computer modelling study published this year forecasts that tropical cyclones will become more intense and frequent.
As Haiyan approached, a trio of storm chasers including Josh Morgerman headed to Tacloban - the city that would bear the brunt of the damage. While satellite imagery showed Haiyan was at least 400 kilometres in diameter, Morgerman reported that from the ground it seemed a small storm, with very destructive winds not starting until around 45 minutes before the centre's closest approach. The main assault lasted only around two hours. "I've been in about 20 hurricanes, and this one was rather bizarre," he said.
This sudden onset and swift passage was also a feature of one of Hong Kong's deadliest typhoons. The unnamed storm struck on September 18, 1906, and the first warning was only given at 8am, with the typhoon gun fired 40 minutes later - by which time the storm had already arrived. A report tells of the wind blowing at terrific force and a deluge of rain. By 11am, the typhoon had passed, and there was a chance to survey the devastation.
Many ships and small boats were wrecked or smashed, and at least 10,000 people - perhaps five per cent of the population - had been killed. Rather as with Haiyan, there was a destructive storm surge.
In 1937, another typhoon killed around 10,000 people, again with a devastating storm surge. In Victoria Harbour, the water rose almost two metres above normal height, reaching Des Voeux Road and Nathan Road. But it was Tolo Harbour that was most impacted. According to a record of the typhoon's toll, "a tidal wave overwhelmed the fishing village of Tai Po, New Territories, and demolished practically all the buildings and fishing boats, causing heavy loss of life. The wave was said to have been 18 feet [5.5 metres] high, and swept into Tide Cove and washed away almost a mile of the railway embankment …."
Here, perhaps, there is a similarity with the storm surge typhoon Haiyan caused at Tacloban - where the water was also funnelled into a narrow bay, and piled onshore.
Tolo Harbour is evidently prone to storm surges. Another occurred during the passage of Typhoon Wanda on September 1, 1962. An account by the Observatory suggested Wanda brought a dome of water up to 50cm high and 160 kilometres across, and as it neared the coast its height increased. The intense winds caused the water to build up in Tolo Harbour, with water covering the railway track in Sha Tin station.
Recently, the city has been spared severe surges and in September, we had a lucky escape. Typhoon Usagi followed a path similar to destructive typhoons of the past, but shifted just to the north of Hong Kong. The Observatory's computer model suggested that with a more southerly track, there could have been a storm surge at least as strong as with Wanda.
As Haiyan approached the Philippines, there were warnings of a storm surge. Yet the mayor of Tacloban, Alfred Romualdez, later told CNN that "storm surge" meant little to people, and if warned of a tsunami they might have been better prepared. In Hong Kong, too, the notion of a storm surge might seem unthreatening. But eventually, another major surge will strike and - exacerbated by rising sea levels - will test Hong Kong with its modern infrastructure, perhaps causing damage in an object lesson about those forgetting the past being doomed to repeat it.
Martin Williams is a Hong Kong-based writer specialising in conservation and the environment, with a PhD in physical chemistry from Cambridge University.