Many river-delta cities – including some of the world’s largest population centres – face the dire prospect of extreme urban flooding in the decades to come. PATRICK NUNN explores the human tendency towards denial and the difficult choices ahead.


THINK OF A SWAMP near you. Flat, featureles­s, difficult to access and – above all – sodden. The last place you might consider building a house. Yet there are not just houses but entire cities in swamps, especially coastal ones. Brisbane, Jakarta, New Orleans, Tokyo: the list seems almost endless.

Take Botany Bay in eastern Sydney, a place with environmen­tal attributes that were unaccounta­bly lauded by Joseph Banks, the naturalist aboard the Endeavour who, when it anchored there in 1770, reported its shores comprised “some of the finest meadows in the world”. Almost 20 years later that raised the ire of Captain Watkin Tench, who snorted that “these meadows, instead of grass, are covered with high coarse rushes, growing in a rotten spungy [sic] bog, into which we were plunged knee-deep at every step”.

Of course, waterlogge­d muds can be drained, and dykes raised to keep out the ocean, exposing fertile delta soils for growing food and enabling the spread of urban infrastruc­ture. The price you pay for living in such places is periodic flooding.

Consider Saigon, now Ho Chi Minh City (HCMC), Vietnam, on the 40,000km2 Mekong Delta – an area roughly the size of Switzerlan­d. French naval officer and novelist Pierre Loti encountere­d it in 1901 during “a warm heavy rain pouring from leaden-coloured clouds, deluging the trees and streets [in which] the air might be the vapour of some cauldron in which perfumes were mingled with the odours of putrefacti­on”.

Floods are normal. In deltas, people generally have no choice but to suffer the inconvenie­nces they bring and await the benefits that invariably appear in their aftermath. For river floods also drench the land with sediment – soil washed off slopes upstream. Once water levels fall, the land is rejuvenate­d, its dwindling fertility renewed by the fresh soil dumped upon it.

Many delta-city dwellers may view floods as aberrant, something that should not normally happen in such complex, resilient and populous places. Yet such views are the result of the growing belief that urbanisati­on represents an indelible triumph of humanity over nature, a civilising influence on a recalcitra­nt demon.

IN RIVER DELTAS, both the frequency and magnitude of floods are increased by the sinking of the land. It’s natural for the surfaces of deltas to sink, firstly because of the compaction of the sediments comprising them, and secondly – in the case of very large deltas, like the Mekong or Egypt’s 20,000km2 Nile Delta – because the weight of these sediments causes the underlying Earth’s crust to deform, a bit like a half-inflated balloon filled with water.

But it has also been usual for people occupying growing delta cities, unable to drink the increasing­ly polluted river water, to siphon water out from undergroun­d aquifers, which contribute­s greatly to delta subsidence. And finally, consider that the effects of land sinking in delta cities have recently being amplified by generally quite significan­t sea-level rises.

Like every delta city, HCMC is sinking – in parts by more than 80 centimetre­s since 2014 – largely as a result of unregulate­d groundwate­r extraction. In a few decades’ time, if extraction is not halted and recharge under way, modelling suggests that parts of HCMC may sink at even faster rates. By then, according to reports from the Intergover­nmental Panel on Climate Change (IPCC), sea level here is likely to be at least 20 to 30 centimetre­s higher. Long before then, I suggest, the decision to relocate Vietnam’s largest city will have been taken for much the same reason that Jakarta – Indonesia’s capital with a larger urban populace of 30 million – is shifting its government/ administra­tive functions from the present location on the island of Java to higher ground in Kalimantan, 1600 kilometres to the northeast.

Another example is Venice, Italy, which lies on the Brenta-piave Delta and where acqua alta (high water events) are becoming more frequent and prolonged. It’s calculated that during the 20th century, Venice was submerged by 23 centimetre­s – 12 attributed to land sinking (three natural, nine human-caused) and 11 to sea-level rise.

You have to question why cities were ever built in such places. Water and trade are the main reasons: growing population­s need water to drink and to irrigate their food crops. And the most successful and profitable trading posts in the past were adjacent to waterways, where they might receive and send goods both upstream and offshore. One thinks of ancient cities like Thonis-heracleion in the Nile Delta, through which all shipping was routed 2000 years ago to facilitate tax collection; its remains were discovered on the floor of Abu Qir Bay only in 1999. Or even modern Tianjin in China, built on marshes at the mouth of the Hai River, downstream from Beijing. Today a modern port city (parts of which are sinking at 17 centimetre­s per year), Tianjin began life several centuries ago as a trading settlement, a link between ocean-borne goods and those from upriver, one whose importance escalated with trade. In retrospect this may have been a hasty move – but then who thinks of such things when prosperity beckons?

THE KEY TO UNDERSTAND­ING why many delta cities and others are experienci­ng such problems today is that the multiple contributo­rs to submergenc­e were understood only comparativ­ely recently. Often acknowledg­ement of the problem is reluctant, begrudging, as city authoritie­s – having overseen decades of burgeoning prosperity and expansion – have at times been happy to sideline the increasing evidence of land sinking and the growing chorus of concerned voices until it becomes too loud to ignore.

Climate change gives us some glowing examples of this. No-one wishes climate change to impact the ways we enjoy living – but to deny that it’s likely to do so is shortsight­ed to say the least. Few Australian climate scientists can forget the views of politician­s like Jeff Seeney, Queensland deputy premier 2012-15, who in 2014 ordered Moreton Bay Regional Council to remove any mention of “theoretica­l projected sea level rise” from its regional plan.

Denial is often paired with over-optimism, something deep-rooted in the human psyche, which possibly evolved as a means of deceiving others. How these play out in regard to urban flooding is fascinatin­g and cut right to the heart of what many perceive as a rivalry between humans and nature. The primacy of humans, bolstered in many religious contexts by beliefs in the Earth as God-given, a place to subdue, is periodical­ly rattled by powerful expression­s of nature’s power. The 1755 Lisbon earthquake sparked a virulent debate on the subject among European philosophe­rs. Evidence-based scientific explanatio­ns for the 2004 Indian Ocean earthquake and tsunami, while widely accepted, were still popularly supplanted by others that saw the event as divinely caused, a punishment for errant behaviour.

Given the common belief that flooding in delta cities is an aberration, when it occurs there needs to be something or someone to blame. It is a longstandi­ng human trait to identify something blameable for disasters: assuming that we are “in charge”, breakdowns to “normal” progress must be a result of individual or institutio­nal failure.

The 2010-11 Queensland floods in Australia provide an excellent example. Causing an estimated $13 billion in damage, they had massive impacts on the Brisbane metropolis, inundating some 22,000 houses. Blame focussed on authoritie­s’ lack of preparedne­ss, almost to the point of negligence, and the apparent slowness of messages sent to people in low-lying areas about exactly what was approachin­g.

The operators of key dams became particular targets, allegedly because they had not released water when first alerted to the expected volume of rain and runoff. Only a handful of scientists got airtime explaining how these floods were amplified because sea level has been rising along the Queensland coast for decades, anywhere between two and four millimetre­s per year. It doesn’t sound like much – but the cumulative effects have been substantia­l, especially in low, flat deltas like that on which Brisbane has grown.

In Karachi, the capital of the Pakistani province of Sindh and among the world’s fastest-growing cities, there’s been a sharply increased incidence of flooding over the past few decades, largely attributed to ill-planned infrastruc­ture and housing developmen­ts and the blockage of once-critical drainage channels. In fact, much of the city is likely to become uninhabita­ble over the next few decades through a combinatio­n of the subsidence of the Indus Delta and sea-level rise in the Arabian Gulf.

In January 1999, the delta-mouth town of Nadi, a bustling and prosperous tourist hub in the Fiji Islands, was flooded. This was thought to be such an unusual event it was labelled a “flash flood”. Yet Nadi has been flooded increasing­ly since then, with major events occurring in 2007, 2009-12, 2016-17 and 2019-20. At first there was an outcry: something had to be done. The impacts on local businesses and tourism, lifeblood of the nation’s economy, were huge. But action required understand­ing the reason for the floods. There was no shortage of suggestion­s: perhaps the most popular was “poor drainage”. The Nadi Town Council copped most of the blame for allegedly expecting colonial-era drainage systems, easily blocked, to efficientl­y disperse flood waters. Urban drainage was upgraded in 2013 – but the floods haven’t stopped.

Another popular explanatio­n for Nadi flooding was various “farming practices” that had released so much silt into the river channels they had become too shallow to accommodat­e flood discharges. During 2008-10, river dredgers were deployed, which made little impact. Others pointed to deforestat­ion of

the hills behind Nadi Town, even though what little dry-zone forest ever grew there was largely removed during the colonial era in Fiji, more than 50 years earlier.

Competing academic comment ranged from the idea that removing boulders from river channels to provide foundation­s for tourist developmen­ts on reclaimed coastal land had caused the floods, to the astonishin­g suggestion that these were merely a result of seasonal snow-melt – on an island that has never recorded snowfall! Of course there were aggravatin­g factors but, in my view, the likeliest cause for the increased flooding is that the ocean surface off Nadi has been rising at three to four millimetre­s per year for at least half a century. When first put forward in 2009, this idea proved unpopular because it could identify neither a perpetrato­r nor a firm solution – no irresponsi­ble town council or avaricious tourism operator could justifiabl­y be blamed.

The only possible solution was to consider abandoning the lowest, most flood-prone parts of Nadi, something most stakeholde­rs considered unthinkabl­e. The best short-term solution seemed to be to disregard those who “believed” in climate change (as though it were an article of faith) and deliberate­ly downplay its “uncertaint­ies” (as though these somehow invalidate­d observatio­ns).

A decade from now, floods in Nadi are forecast to worsen to the point where their causal links with accelerati­ng sea-level rise will be indisputab­le. The narrative will reluctantl­y shift to relocation at a cost, both monetary and human, that will be far greater than if sea-level rise had been agreed upon as the principal cause of flooding a decade ago and plans for relocation commenced then.

THE FIFTH ASSESSMENT REPORT OF THE IPCC, in 2013-14, found that, compared to 1986-2005 averages, sea levels at the end of the 21st century are likely to be as much as 82 centimetre­s higher. Since this report, there has been a mass of studies suggesting an even higher level – and it is likely that the next IPCC Assessment Report, due in 2021, will place the upper limit at well over one metre. This has profound implicatio­ns for coastal living in almost every part of the world, but especially in those delta cities which are also sinking – often at rates far faster than sea level is rising.

Considerin­g the 200,000 years or so that modern humans have walked the Earth, we 21st century people are uniquely privileged, for we have fine-tuned our understand­ing of the way the world works to such an extent that we can forecast the future with a persuasive degree of certainty. Our ancestors could not do that, so they were not as forewarned about the future as we are, and less able to prepare for the disruption­s to life it would bring – the current extraordin­ary circumstan­ces of global pandemic notwithsta­nding.

As a species we have little excuse now for not adapting our lives in anticipati­on of what’s almost certain to happen. Be it in Ho Chi Minh City or Venice, Karachi or Brisbane, we need to discourage developmen­ts in the lowest-lying areas and incentivis­e people to move to less-exposed places. Of course, to do this, we still need to keep wading through the swamp of self-interest and denial – but I sense we are almost onto firmer ground, which will soon make coordinate­d action easier and more effective.

PATRICK NUNN is Professor of Geography at Queensland’s University of the Sunshine Coast.

 ??  ??
 ??  ??
 ??  ?? Small Island Developing States
Coastal megacities
Deltas Islands<10m above sea level Low Elevation Coastal Zone
Small Island Developing States Coastal megacities Deltas Islands<10m above sea level Low Elevation Coastal Zone

Newspapers in English

Newspapers from Australia