Our planet is a place of constant change.
Each year, the seasons shift and life is transformed.
But there are places where the changes are so epic in scale,
they can be seen from space.
In this series, we reveal three of the most miraculous transformations.
The islands of Svalbard.
Within a few weeks, frozen wastelands burst into life.
The African Okavango.
A desert transforms into a magical water world.
And the mysterious forests of New England
erupting in a blaze of seasonal colour.
Life finds the most ingenious and surprising ways to thrive...
..in the world's most fast-changing landscapes.
The Kalahari basin.
2.5 million square kilometres of flat sand and scrub.
This desert stretches across southern Africa.
But at its heart lies a river.
A river that never reaches the sea.
And once a year, it floods.
Over five months, waters spread across a vast area of the Kalahari,
transforming it into a wonderland.
The Okavango Delta.
This is the story of how nature creates a unique,
flourishing wetland out of one of earth's great deserts.
Our story begins in the heart of the Delta.
The dry season is well advanced
and water is becoming scarcer by the day.
At this time of year, predators rule.
Animals have another six months to wait
before the flood turns this land back into a lush wetland.
Sable antelope.
After grazing on dry grass, they have to drink at a stagnant pool.
But they're nervous.
Predators watch their every move.
For a leopard, though, a sable's size
and lethal scimitar horns pose too much of a risk.
There are plenty of easier targets.
A family of warthogs.
GRUNTING
Where once there was a wide river,
they use their tough snouts to truffle for bulbs.
But it's hard work in this dry, sun-baked ground.
And having your snout in the sand is decidedly risky.
GRUNTING
SQUEAL!
FRANTIC SQUEALING
SQUEALING
The leopard drags its kill to a hiding place,
where it can dine in peace.
The warthog will keep it going for a week.
The dry season means good hunting for top predators.
For everyone else, food is scarce.
Chacma baboons survive through their knowledge...
..and eclectic taste.
BUZZING
Elephant dung is a valuable source of seeds and insects.
CHATTERING
But it looks like there's an appealing alternative.
A tree that fruits even in the dry season.
A fan palm.
The fruit is nutritious, if a bit tough and pithy.
But what's this?
Elephants will eat virtually any vegetation.
And fruit is their favourite.
They can smell it from several kilometres away.
For the baboons, the feast is over.
TRUMPETING
The fruit may be 20 metres up and out of reach,
but the elephant's strategy is simple.
Brute force.
For a crafty baboon, though, it sometimes pays to hang around.
It's spotted one that the elephants missed.
Nearby, at a shrinking pool, something agitates the water.
Mouths gulp at the surface.
It's crowded with giant catfish up to a metre-and-a-half long.
There's no oxygen left in the water for their gills to use.
But these fish also have lung-like organs that breathe air.
Every day, under the Kalahari sun, more water evaporates.
African fish eagles gather expectantly for a banquet.
In desperation, some catfish attempt to make a run for it,
using their fins to propel them.
Now exposed, they are easy targets for eagles and jackals.
SQUAWKI NG
These catfish have run out of time.
Within two weeks, the pool has vanished.
When it floods, there will be plenty of water for everyone.
But now, at the end of the dry season,
elephants must keep walking in search of water.
LOW ROAR
Her calf needs 15 litres of milk a day,
so she must find over 100 litres of water for both of them.
But elephants have a special technique to get at fresh water.
No other animal has such power.
Using their tusks, they pile-drive into the flood plain
until they reach water beneath the surface.
TRUMPETING
In doing so, elephants create a lifeline for others.
A hyena and jackal wait their turn.
Elephants with calves are not to be messed with.
So they dive in when they can.
But this jackal may have pushed its luck a little too far.
CHATTERI NG
BI RDSONG
For insect-eating birds, food is increasingly hard to find.
This mound makes a good lookout post.
But if only it knew what's inside.
It's a fortress for Macrotermes termites.
A colony a million strong.
A termite's mound is just the hub of an underground city.
Six kilometres of foraging tunnels.
Here, the Macrotermes process dead vegetation into food.
The mound is perfectly engineered
to keep air at constant temperature and humidity.
Protecting the termites from drying out.
But these mounds will also prove essential
for the survival of many other species when the floods come.
By the end of October, dryness and increasing temperatures
turn the once-lush Okavango Delta into a tinderbox.
FLAMES ROAR
But these birds seem to be attracted to the flames.
For the lilac-breasted roller and the fork-tailed drongo,
it's a great opportunity.
Because the fire flushes out a bounty of insects.
Up to a quarter of the Okavango flood plain
can burn in a single year.
For most of the plants and animals that live here,
the end of the dry season can't come soon enough.
THUNDERCLAP
RAIN PELTS
November brings a little respite to the parched land.
THUNDERCLAP
Warm, humid air moves in from the tropics.
Rain in the Kalahari.
Just enough to green the delta.
BIRDSONG
CHATTERING
The baboon troop has grown in number.
SQUEALING
These youngsters were born just in time to enjoy what the rains bring.
More trees have come into fruit.
It makes for a delicious breakfast.
But there's a downside to such a wonderful scent.
TRUMPETING
Sure enough, elephants aren't far away.
TRUMPETING
GENTLE ROARING
The troop scatters.
SQUEALING
Maybe it's time to move on.
Mothers carry their newborns safely underneath,
where they can keep suckling.
But the older ones must learn to ride on top.
CHATTERI NG
On these open plains, the troop must stick together.
Some have already lost limbs to leopards.
All these animals will soon face a new world.
The Kalahari rains may have provided some temporary relief,
but a much greater change is on its way.
In distant mountains beyond the Kalahari,
the tropical air now brings much heavier downpours.
Rain, from highlands to the north,
cascades ultimately into one river.
The Okavango River.
It creates a pulse of high water
which takes two months to snake over a thousand kilometres
to the top of the Okavango delta.
It will still be another month
before the floodwaters reach the heart of the delta.
Here, the river always flows
and is home to several thousand people, such as Sinabe.
His people are descendants of both Kalahari nomads
and fishermen from central Africa.
As the river rises, water spills on to the surrounding land.
Creating shallows ideal for spear-fishing.
The rising pulse of water continues onwards.
South, towards the dry heart of the delta.
But to understand what happens next, we have to go back in time.
Two million years ago, great cracks ripped through the desert floor.
The land warped to create the shape of the Delta we know today.
The faults define the start and finish lines for the flood
which is to come to the main delta.
The dry plains in the heart of the Delta will soon be transformed.
GRUNTING
Life here is about to be turned upside down.
GRUNTING
SQUEALING
But for this family of warthogs,
there's still a bit of time to get some truffling in.
The last rains softened the ground.
And now, getting at those tubers is much easier.
For the cunning baboons, it's an unmissable opportunity.
They muscle in to enjoy the fruits of the warthogs' hard work.
GRUNTING
SQUAWKING
The baboons may have no manners,
but the warthogs don't really seem to mind.
Perhaps it's because the baboons provide extra security.
But this is one food source that will soon disappear.
Hidden in the reeds, it starts as the tiniest trickle.
The beginning of one of Africa's greatest floods.
As rising water spills into the main delta,
it slows and spreads into countless, tiny rivulets.
RHYTHMIC DRUMBEAT
Travelling at barely a kilometre a day,
the flood will take another four months to cover the delta.
But straightaway, wherever water touches the land,
it makes a remarkable impact.
Common sand frogs spend most of the year
buried half a metre underground.
But now, water floods their burrows and forces them to the surface.
They inflate to scare off any predators.
He's off to find a female.
For tiny creatures whose homes are in the way,
the trickle is more like a tsunami.
Ants are forced to evacuate their nest.
An easy snack for blacksmith lapwings.
Termites now face the flooding of their colony.
They beat a hasty retreat to the safety of their mound
as their tunnels start to flood and collapse.
But in doing so, something miraculous happens.
The tunnels seal themselves up.
This blocks the flood's underground advance
and forces the water back to the surface.
Back inside the mound, the termites are safe.
Incredibly, the flood provides just the opportunity they need.
Their fragile castle, made of sand,
requires constant maintenance and rebuilding.
But the soil, now softened by floodwater,
is easy to transport to damaged parts of the mound.
Gradually, thousands of termites reconstruct their fortress.
Repairing these mounds isn't just good for the termites.
These structures help to create something vital
for all the delta's wildlife.
Its islands.
And it all starts like this.
Dung.
Readymade fertiliser laden with fruits and seeds.
Floodwater soaks up the dry side slopes of the mound
to create the perfect bedding for new plants.
Gradually, season-by-season,
termite mounds become home to more and more plants.
As they grow, they attract more animals,
which in turn bring with them the seeds to grow even more plants.
Sycamore fig, fan palm, marula.
Until the termite mounds are barely recognisable
under their lush green canopies.
As it floods, raised areas around termite mounds become islands.
They provide food, shelter and a refuge throughout the year
for everything from elephants to baboons and birds.
In the delta, once featureless desert,
there are now around 150,000 such islands.
For a lot of thirsty animals,
the floods simply mean sweet drinking water.
Elephants no longer need to dig holes.
TRUMPETING
CHATTERING
GRUNTING
Baboons, too, seem to delight in the precious liquid.
Curious youngsters, encountering the flood for the very first time,
don't seem to know quite what to make of it.
The sand may look barren,
but wherever the water touches it, something magical happens.
Within a couple of days, billions of freshwater plankton
begin to awake and hatch.
Such tiny creatures are the delta's secret ingredients.
The foundation of its food chain.
Meanwhile, in a deeper channel,
a mountain of foam has appeared.
It has been created by a pair of African pike.
Notoriously aggressive,
but caring parents that watch over their offspring.
Hidden safely underneath the foam,
hundreds of fish eggs are beginning to hatch.
The fry remain attached to the foam until they are well developed.
And now, the delta offers plenty for them to eat.
The tiny pike fry join small, hungry fish of 70 different species,
swimming though the shallows
in a nutritious soup of freshwater plankton.
BIRDSONG
Before long, the skies fill with birds.
One of Africa's greatest wildlife spectacles.
Travelling nomads from far and wide.
The reason they're here?
Wherever water covers the land, it fills up with little fish.
Each of the birds has its own special technique for catching them.
A saddle-billed stork jabs at its prey.
African spoonbills have the perfect equipment
for filtering out the finest morsels.
Black egrets use their wings to form canopies over the water.
The shade lures nervous fish desperate for cover.
Others attack directly from above.
A pied kingfisher.
At 25 centimetres long,
it's the world's largest hovering bird.
Hovering demands a lot of energy,
so they have to catch a quarter of their weight in fish every day.
Keeping its head perfectly still,
about ten metres above the water, it sees movement.
Then drops in a controlled dive.
If the fish sees it, the kingfisher can still abort and save energy.
If not, it commits and dives rapidly.
It's worth the effort.
Hovering allows them to hunt in the middle of the plains,
where the pickings are especially rich.
The bird kills its prey with a blow to the head.
But before it can swallow, it must flip the fish, head first,
or the spines will stick in its throat.
Within a few months, another type of organism
vital to the delta breaks the surface.
Dozens of species of aquatic grasses,
sedges and water lilies.
At dawn, day lilies open
to attract pollinating bees and flies.
As dusk approaches, the day lilies begin to close,
and give way to the night shift.
Night lilies open their brilliant petals...
..bright enough to attract insects in the moonlight.
Water lilies, flourishing in the middle of the Kalahari desert.
Perhaps the greatest miracle of the delta.
And only possible thanks to one thing.
Nature has found a unique way to keep the water of the Delta
pure, very low in toxic salts.
Its secret lies with those extraordinary islands.
Trees on the islands act as pumps,
sucking in water from the surrounding swamp.
As they do so,
salts in the water are deposited in the sand of the islands.
By extracting salt from the water,
it's as though the islands are kidneys,
removing waste from the bloodstream.
This way, the islands keep the Delta's waters fresh
and able to nurture abundant life.
As the morning sun heats the ground, rising vapours everywhere
reveal that water has spread right across this plain.
It's a transformation that turns the tables between predator and prey.
Red lechwe appear in large numbers, looking for their favourite food...
..tender aquatic plants.
But a hyena hopes to take advantage of their distraction.
It just needs to get a little closer.
Time to run for it.
Lechwe have large splayed hooves
that allow them to bound at speed through shallow water,
giving them a big advantage over any predator.
It's an adaptation that helps to protect them
during the time of flood.
Soon the aquatic vegetation sprouts everywhere
and the water becomes impassable.
But crisscrossing the flooded plains,
highways through the reeds appear.
And here's their creator - a hippopotamus.
He's a grazer and thinks nothing of bulldozing a way through.
As he does so, he excavates a channel.
And it's not only hippos that have to find a way through.
In the far north of the Delta,
Sinabe rows through dense beds of reeds.
To get through, he seeks the help of the spirit of the river.
Deep in the reeds, he discovers a hippo channel.
It's a highway for fish, so the perfect place to rig a net.
Sinabe's village is on the edge of the flood plain.
His family know that as long as the Delta provides,
they will never go short of food.
He smokes the bream to preserve it
for days when the catch isn't quite as good.
Meanwhile, his family weave baskets out of grass from the flood plains.
Later in the year, they will be used for catching fish.
By July, in the heart of the Delta,
the once-dry savanna has become a lush water-world.
But this transformation has an odd effect on the baboons.
SQUEALING
Each has developed its own funny walk.
SCREECHING AND GRUNTING
SCREECHING
All that is, except for the baby - who just gets a soaking.
SCREECHING
It seems likely that baboons don't much enjoy being in the water -
or they may be nervous of something in it.
Crocodiles are everywhere.
For the troop, a flooded Delta is a lawless place,
but a threat worse even than a crocodile has appeared.
Lone male baboons.
The shrinking of territory on land
forces the loners into contact with troops.
They may fight the troop's alpha male for control.
If the stranger wins, he may also kill the young
and mate with the females.
An incumbent alpha male must keep a close eye on any rival.
HE BARKS
To survive, it is crucial that he lay down his authority.
BARKING AND GRUNTING
GRUNTING
ROARING
SCREECHING
ROARING AND BARKING
SCREECHING AND ROARING
BARKING
GRUNTING AND SQUEALING
SCREECHING AND SQUEALING
GRUNTING
Insurgents must be sent packing.
As the Delta floods, everywhere, tension seems to be mounting.
Not least in the hippo community,
where their watery territories are expanding dramatically.
Here, too, there is a young challenger.
The territory's resident bull snorts a warning.
HE SNORTS
The adversaries declare their ownership of the pool
by vigorously spreading dung with their tails.
SNORTING
They yawn to display their weaponry -
huge ivory tusks.
SNORTING
First, a test of strength.
SNORTING
The old bull makes a temporary retreat.
Females have a vested interest in the outcome.
They will only be prepared to accept a mate
that can hold his own in a fight.
The resident bull retaliates brutally.
SNORTI NG
Hippos will often fight for hours and sometimes to the death.
Finally, a brutal headlock - the coup de grace that settles
it for the older male -
expelling the pretender from his territory.
Which means the resident bull passes the test
to sire this year's crop of baby hippos.
GRUNTING
The young male has been injured during the retreat,
his flank exposed to his furious pursuer.
At least nature has arranged for him to be nursed - by these oxpeckers.
They eat anything that might cause an infection.
The pain is probably worth it
and he should survive to fight another day.
By August, the floodwaters finally reach
the Delta's southern fault line, its maximum extent.
The Okavango is now one of the largest inland deltas in the world.
The whole Delta is linked by water - shallow flood plains, pools,
and deeper channels all fed by the Okavango River.
Billions of fish that fill the plains have grown rapidly.
And Sinabe's wives and daughters are ready for them with their baskets.
SINGING IN AFRICAN LANGUAGE
SINGING CONTINUES
SINGING STOPS
Bulldog fish will make a fine stew.
In the main river, something strange is happening.
The waters appear to be boiling.
It's catfish, taking gulps of air at the surface.
And they are here in their millions.
Before the flood recedes, they return from their hunting grounds
in the far reaches of the Delta to the safety of the deep channels.
Amongst the papyrus, they hunt smaller fish.
Flocks of egrets arrive to join in the feast.
No-one is safe in the mayhem.
African fish eagles swarm and dive-bomb the catfish.
Millions of fish that grew fat out in the flood plains
bring life back to the river that brought them water.
When it's needed most,
the flood creates a vast oasis in the desert - a wonderland.
Its 10,000 square kilometres of crystal waters
attracting animals from all over the dry Kalahari desert.
HE ROARS
But these waters will never reach the sea.
They will soon begin to evaporate or simply sink into the Kalahari sand,
as the Okavango Delta gradually returns to dry savanna.