In November Sài Gòn was swamped with record rainfall as the remnants of typhoon Usagi passed over the city. Whilst it would be wrong to say it was caused by climate change there is no doubt that like all weather events these days climate change made it worse. And as the planet begins to warm even more quickly it provides a grim portent of things to come.
The impacts of a changing climate on storms such as these are multiple. First of all sea levels around Saigon have been rising by more than 3.5 mm a year. Whilst a rise of more than 10 cm over the past 30 years may seem insignificant such a rise can easily make the difference between an inconvenience and a flooded a house or drowned motorbike.
It was the combined effects of tide and rain that proved so devastating at the weekend. The arrival of the storm coinciding with a particularly high tide meaning that the intense rainfall had nowhere to go. And as well as raising the high water mark climate change is also increasing the intensity of rainfall events. Put simply hotter air can hold more water vapour which translates to more rain when it condenses. Across the globe precipitation events have become around 10% heavier over recent years. And Saigon is no exception. Sunday’s rain was record breaking, with a number of gauges surpassing 400 mm of rain for the first time. To put that into perspective over the 40 years from 1962 to 2001 in Ho Chi Minh City there were only 9 rainfall events with precipitation of over 100 mm. The subsequent 14 years saw 30 events. Even a year or two ago a 200 mm event was seen as remarkable. And so the city’s infrastructure has simply not been designed for such episodes with many of the old sewers only able to cope with 30 to 40 millimeters of rain.
The jury is still out on whether climate change is leading to an increase in the number of typhoons. There is still a lot of yearly variances in the number of occurrences. Last year a record 16 storms hit Vietnam, whilst this year there have been only 9 so far. What can however be discerned is a small but none the less significant increase in the strength of storms.
Acting in tandem with these man-made changes to our climate are the man made changes to the city. Previously the lowest areas in the city acted in two ways to limits flooding. Firstly they provided drainage to enable flood waters to flow out of the built-up area. Secondly these swampy areas acted like a giant sponge absorbing excess water from the sea and sky. However it is these previously undeveloped areas which have been the focus of the city’s relentless expansion over the past decade or so. Many of the intricate network of canals which served to dissipate the flood waters have been filled in. And the swampy lowlands where water previously flooded have been replaced by flood defenses. All that water has to go somewhere and now it goes into areas that never previously flooded.
Finally the breathneck development of the city is having another consequence. It’s sinking. The weight of the roads and high rise buildings combined with the extraction of groundwater is causing the city to subside at an even faster rate than the seas are rising. 14 millimeters per year in some districts.
All of which combined at the to produce a perfect storm. The worst flooding the city has ever experienced. But it won’t remain the worst event for very long. It’s going to get worse. Much worse. And quickly.
Sea levels are now expected to rise by at least one meter this century. And that’s the minimum. 2 meters is possible and perhaps even more. Some have speculated that rises in the order of 7 m may not be out of the question. A Dutch flood defence expert told me that two meters of sea level was probably the maximum practicable height that could be defended. And that’s in the Netherlands with decades of expertise and quality control which would struggle to be replicated in Ho Chi Minh City.
This is what the city would look like if the sea was 2 m higher and not even on a day of extraordinary flooding but twice a day every day . High tides would inundate far more and a record flood doesn’t bear thinking about. All of which effectively means that much if not all of the city may well need to be abandoned before the century is out. Sobering thoughts completely at odds with what is actually happening. Development continues apace on some of the lowest and most flood threatened areas of the city. Developments signed off decades ago using sea level projections which are now hopelessly out of date. Part of that responsibility lies with the IPCC (UN Intergovernmental Panel on Climate Change) whose sea level rise projections have been and still are incredibly conservative. For a long time they failed to include any estimation of ice cap melting because there was a great deal of uncertainty over how much it might be. When in reality under the precautionary principle they should have cautioned they other way. However we also can’t ignore the interests of developers and politicians most of whom have consistently failed to take the changing realities of climate change into consideration for the sake of short-term gain.
As usual it will be the most vulnerable in society who suffer most. Whose homes will be inundated first by the water which is displaced by the construction projects of the rich. Of course it won’t be long before other sections of Vietnamese society will begin to suffer. The realisation that some of the most expensive real estate in the country is will soon be worthless will cause property prices to collapse. If that doesn’t destroy the economy then the loss of up to 50% of the countries agricultural production in even more vulnerable low lying areas In the Mekong and Red River Deltas almost certainly will. And the 10 – 20 million refugees driven from their lands by that inundation will further compound the problems. So sad to think that just when they country was beginning to thrive after recovering from centuries of occupation and war it may about to be plunged into even greater suffering and loss caused by the very same western powers that destroyed it before.