SinergiaLab · Essays · 2026-10-20
Frog cities: living with water and its tides
Cities that seal their lower levels, spend months underwater and rise again. Not a fantasy of the future: a way of living we unlearned
In UnitedCities, our science fiction saga set in the year 2200, there are truly amphibious cities. They neither float nor defend themselves: they seal their lower levels, spend whole months underwater and rise again when it recedes. Frog cities, living with nature instead of fighting it.
It looks like a liberty of fiction and it is something else: a turn in our relationship with life itself. What follows is why, and why we did not invent that way of living.
Three ways to get water wrong
Faced with rising water, humanity has tried three answers, and all three share a premise that is almost never discussed.
The first is to fight. The dyke draws a line and bets on never being wrong. It is a bet with an uncomfortable feature: its failure mode is binary. The dyke holds or breaks entirely, and the day it breaks it does not let in a little water but all of it. It is immensely strong until it stops being so.
The second is to flee. Managed retreat abandons the coast and books the loss. It is honest and sometimes the only sensible thing, but its balance is always in the red: what is gained is not dying, and what is lost is the place.
The third is to float. To rise above the water and stay dry while it passes. It sounds more modern than the other two and at bottom repeats the same gesture: dodging.
All three take for granted that human life has to be continuous and has to be dry. That if the water arrives, something went wrong. That premise is so old and so widely shared that it stopped looking like a decision, and that is exactly where it pays to press.
The frog and the duck
There is a misplaced word at the centre of this conversation. Today’s architecture calls amphibious a building that rests on firm ground when it is dry and floats when the water rises. The best-known example is the Formosa house, on the Thames: it sits on fixed foundations inside a dry dock, and when the flood fills the dock, it rises and floats. The term comes from amphi, both, and bios, life: two modes of existing.
But as a metaphor it fails the simplest test. An amphibian lives in two media, and one of them is underwater. A frog spends time above and time below. That house is never underwater: it floats on the surface or rests on the ground. That is not a frog, it is a duck.
The distinction is not wordplay, because it marks where what we know how to build ends. The Amphibious Cities of UnitedCities do something else: they seal their lower levels, stay submerged for months and rise again when the water recedes. They do not dodge the water from above. They go through it.
And so the question stops being technical and becomes another one: what has to change in a city for being underwater not to be a catastrophe?
From event to season
The change is not a technology, it is a change of category: the flood stops being an event and becomes a season. It is not something that happens to the city, it is a phase of the city. It sounds minor and it changes everything, because a catastrophe is prevented and a season is inhabited.
The hopeful part does not lie in the technical apparatus.
It is not that we avoid the flood: it is that we stop needing to avoid it.
An idea is worth what it forces to change around it, and this one forces a lot. The city comes to have two calendars and two lives, the dry months and the submerged months, and the passages between them become the dates that organise the year. The lower levels are no longer protected, they are designed wet: materials that do not mind, nothing valuable to rescue, sealing as routine rather than rescue. Nor does the submerged level sit idle; it produces something else, water crops where there used to be street. The flood brings sediment and fish, so it is income, not loss. And the city that truly lives this way holds festivals when the water rises and when it leaves, which is where you can tell whether the idea is true.
All this sounds like science fiction, and in UnitedCities it is. But each of those five consequences existed, and in some places still does.
The Nile: a civilisation whose year began with the flood
The calendar of ancient Egypt had three seasons. The first was called Akhet, meaning Inundation. Then came Peret, growth, when the land reappeared; and finally Shemu, harvest.
It is worth pausing on that for a second. It was not that the year had an annual problem called flooding. It was that the year began there. Going underwater was the first of the three things that happened, and the other two depended on it, because the flood deposited the silt that made the soil fertile. Without flooding there was no surplus, and without surplus there was no Egypt.
This is not remote archaeology. The cycle worked for millennia and switched off in 1970, when the Aswan dam was completed and Lake Nasser filled. The reservoir could hold back even the highest floods, and the annual inundation simply stopped happening.
Fifty-six years ago. There are people alive who saw the last Akhet.
Tonlé Sap: the river that turns around
In Cambodia there is a river that changes direction. When the Mekong rises, it pushes so much water that the Tonlé Sap reverses its course and runs inland, filling the lake. Later, when the Mekong falls, the river runs outward again. The same channel, both directions, every year.
In Kampong Phluk people live with that. The houses stand on stilts six to ten metres tall driven into the lakebed, built to withstand strong currents. And the interesting part is not the stilts but what happens beneath them.
In the dry season the ground under the houses dries out and people walk between the pillars: there the fish is dried and salted, bamboo traps are built, nets are mended. When the water rises, that same space becomes a mooring, boats become the only transport and the catch comes up the stairs to the home.
Nothing moved. Nothing was protected. The same square metre is two different things depending on the month, and neither is the emergency of the other. It is the frog city working today, at village scale, without a single piece of technology from 2200.
Chinampas: making land with water, and the bill that came later
The chinampas of Xochimilco are called floating gardens and they do not float. They are artificial islands raised from the lakebed: a rectangle is staked out in the shallows, fenced with a weave of reeds underwater, and filled with mud, sediment and decaying vegetation until the surface emerges. Trees are planted at the corners to anchor it, the ahuejote and the ahuehuete. Between plots run canals wide enough for a canoe.
The mechanism is a closed loop. The mud that builds up in the canals is dredged and thrown back on top of the chinampa: that keeps the canals open and returns nutrients to the soil. The ditches provide permanent water, so crops do not depend on rain. Up to seven harvests a year. That is what fed Tenochtitlan.
In the taxonomy of frog and duck, the chinampa is neither. It is a third stance: it does not fight the water, does not flee, does not float on top. It makes land with water. It eats the lake and turns it into soil. It is closer to the mangrove or the coral than to an animal that swims.
And here is what sets this case apart from the other two: it also sends the bill. After the conquest the dams and sluices were destroyed, the lakes were drained and the chinampas were gradually abandoned. Today Mexico City sinks around 35 centimetres a year, built on the dry bed of Lake Texcoco, through aquifer pumping and sediment compaction. There is scientific debate on how much each cause weighs, but not on the chain: the lake was dried, the city was built on top, the water below is pumped out. And as the sediment compacts, the sinking is permanent.
The same city that fed on water now sinks for having rid itself of it. There is no need to imagine the consequence of choosing the dyke: it is happening, it is measurable and it has a postal address.
Titicaca: the best duck in the world
The floating city is not a promise of the future. It exists, it is centuries old and it sits on the altiplano.
The islands of the Uros, on Lake Titicaca, number about ninety. They are made of totora reed: a base of root blocks that float because they hold trapped gas, lashed together, and on top layers of cut reed laid crosswise forming a spongy floor a metre or more thick. Ropes and stakes hold them so they do not drift, and in principle they can be untied and moved.
It is one of the most ingenious inventions this continent has produced. And yet, for what we are discussing here, it is a duck, for two reasons. The first: they never submerge. They stay on the surface by sheer work, because the reed below rots and must be replaced from above all the time. If the work stops, it sinks, which brings them closer to the dyke than one would expect: a line held with continuous effort, with a single mode of existing. The second says the most: the Uros did not go to the water to live with it, but to escape from people. They are a people older than the Incas and, by their own account, took to the lake as a defensive strategy against more powerful neighbours. The water was a refuge from a human enemy, not a relationship with nature: the stance of escape, brilliantly executed, but escape all the same.
Three continents, the same answer, the same abandonment
Placed side by side, the cases say something none of them says alone.
Three solutions that appeared independently on three continents, with no contact between them, solving the same problem with the same intuition. And all three in retreat, at roughly the same time, because of recent decisions of our own.
The convergence is the data point. When three cultures separated by oceans and centuries arrive at the same answer, the answer is probably right. And when all three are abandoned within a few generations, the mistake is probably ours.
So the frog city is not a fantasy about the future. It is a skill we had and are finishing losing. We are not inventing a way of living: we are recovering one we unlearned.
What UnitedCities adds is not the idea. It is scale and time: taking it from the plot and the village to the whole city, and from the seasonal flood to whole months underwater.
The dyke is not a structure, it is a belief
So far we have treated the three stances as engineering options. They are not. They are the same belief built in concrete.
Fighting the water assumes the water comes from outside. That there is a human inside and a natural outside, and a border between them that must be held. The dyke is that border made material: a line that says up to here the world, from here on us. Floating is the same belief with better manners, because it is also about not touching. And fleeing accepts defeat without questioning the premise: we leave, but we are still the ones inside.
That is why the frog's stance is not a technical improvement on the other three. It is incompatible with them. You cannot live with the tides of water while believing water is something that happens to you from outside. First you have to let go of the border.
That is what in UnitedCities we call [Biobelonging](?p=the-three-pillars-of-unitedcities), and it is what the [Manifesto](?p=the-unitedcities-manifesto) said: the separation between humanity and nature never existed. All that existed was the belief in it, and the works we built to sustain it.
Seen from there, the three cases in this article read differently. Egypt, Cambodia and Xochimilco were not technically superior to us. They were less separate. Nobody calls the first season of the year Inundation because of an engineering decision. You call it that when the flood is not something that happens to the people, but something the people are.
And Mexico City is the limit case, because there the belief can be measured. The lakes were drained to stop being a lake city, the city was built on the dry bed, the water below was pumped out. The border held for five centuries. And the bed is taking the city back, thirty-five centimetres a year, irreversibly.
Nature neither negotiates nor punishes. It only keeps the books, and collects late. That delay is what lets us believe we won. In our saga, the Planetary Health Index is exactly that accounting made explicit and punctual: the bill Mexico City received five hundred years later, arriving on time.
Water is the example, not the argument
The frog city is, at bottom, a thesis about robustness: a system that only knows how to exist in one way is fragile, however strong that way may be. The dyke is immensely strong until the day it is not. The Uros island floats as long as someone replaces the reed. A city that only knows how to be dry needs the world to cooperate.
What makes a civilisation hard to kill is not the height of its defences. It is the number of ways it has of remaining itself.
And that does not apply only to water. It applies to any system we bet will never fail: a power grid, a supply chain, an economic model, a technology we depend on entirely. The useful question is almost never how high we can build the wall. It is what we do the day the water comes over the top, and whether we have rehearsed a second way of being alive.
And having two modes is, at bottom, ceasing to believe ourselves outside. A city with a single mode is defending a border. A city with two is accepting that it belongs to something that changes.
Nature shuffles and deals again. It always has. The question is not how we stop it from dealing, but which cards we intend to keep playing with.
In UnitedCities our cities are true frogs. What is called amphibious architecture today is, in fact, duck cities.
Sources
- [Flooding of the Nile](https://en.wikipedia.org/wiki/Floodingofthe_Nile), on the three-season calendar, the silt and the end of the cycle in 1970.
- [Kampong Phluk and the cycles of the Tonlé Sap](https://seasia.co/2026/09/06/kampong-phluk-a-high-stilt-settlement-adapting-to-tonle-saps-water-cycles), on the stilts and the double use of space.
- [Chinampa, Wikipedia](https://en.wikipedia.org/wiki/Chinampa), on construction, canals and the seven harvests.
- [Groundwater pumping is causing Mexico City to sink, Eos](https://eos.org/articles/groundwater-pumping-is-causing-mexico-city-to-sink), on the 35 centimetres a year.
- [Floating islands of the Uros, laketiticaca.com](https://laketiticaca.com/guides/floating-islands-uros-complete-guide-to-visiting-the-reed-communities/), on totora construction and the defensive origin.
- [BACA Architects, Formosa amphibious house](https://www.baca.uk.com/research/case-study-amphibious-house) and [European Environment Agency](https://climate-adapt.eea.europa.eu/en/metadata/adaptation-options/floating-and-amphibious-housing), on the difference between floating and amphibious in architecture.
Claudio Pousada. Director, co-writer and producer of UnitedCities.
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