0:00:14 > 0:00:16Of all our planet's forces,
0:00:16 > 0:00:21perhaps none has greater power over us than water.
0:00:24 > 0:00:29For me, water's the most magical force on Earth.
0:00:30 > 0:00:34The presence of water shapes, renews and nourishes our planet.
0:00:34 > 0:00:36Oh, my gosh! You're getting all wet there!
0:00:41 > 0:00:43It's our planet's lifeblood.
0:00:43 > 0:00:45It pumps through it continuously,
0:00:45 > 0:00:49delivering vital ingredients for life. Ah, it's glorious.
0:01:00 > 0:01:03Water makes Earth alive.
0:01:06 > 0:01:09Yet water is just one of the ways
0:01:09 > 0:01:12that the power of the planet has shaped our lives.
0:01:14 > 0:01:17The Earth has immense power...
0:01:21 > 0:01:25..and yet that's rarely mentioned in our history books.
0:01:26 > 0:01:28I'm here to change that.
0:01:30 > 0:01:35In this series, I'm exploring four great planetary forces
0:01:35 > 0:01:38that have influenced our history.
0:01:43 > 0:01:45The power of the deep Earth...
0:01:47 > 0:01:50..that fuelled technological innovation.
0:01:52 > 0:01:54Wind.
0:01:54 > 0:01:57It has shaped the fate of entire continents.
0:01:57 > 0:01:59And fire...
0:02:02 > 0:02:05..which gave us the power to conquer the planet.
0:02:06 > 0:02:09But I'm going to start with water.
0:02:10 > 0:02:15The magic of water is that it's constantly transforming itself,
0:02:15 > 0:02:20shifting between guises and from place to place.
0:02:20 > 0:02:25Our struggle to control it has been behind the rise and fall
0:02:25 > 0:02:28of some of the greatest civilisations on Earth.
0:02:54 > 0:02:57The centre of the Sahara Desert in North Africa.
0:02:59 > 0:03:02One of the driest places on Earth.
0:03:07 > 0:03:11I'm over six hours' drive from civilisation.
0:03:13 > 0:03:18Temperatures here regularly reach 40 degrees Celsius,
0:03:18 > 0:03:21and there's less than a centimetre of rainfall each year.
0:03:23 > 0:03:24Ah...
0:03:27 > 0:03:29The whole thing's moving.
0:03:30 > 0:03:31(HE STRAINS)
0:03:32 > 0:03:35It's like walking on water.
0:03:36 > 0:03:39Yet hidden amongst these dry dunes are clues
0:03:39 > 0:03:45that point to the dramatic influence the planet has had on human lives.
0:03:52 > 0:03:55I've come here because although you'd never know it,
0:03:55 > 0:03:59the story of this place is all about water.
0:03:59 > 0:04:03The clues are etched into that rock face there.
0:04:03 > 0:04:08Prehistoric rock art dating back 6,000 years,
0:04:08 > 0:04:11and depicting the most unlikely cast of characters you've ever seen.
0:04:15 > 0:04:17Wow, what is that?
0:04:17 > 0:04:19It's a giraffe...
0:04:19 > 0:04:22It's a giraffe, look at it, there's the neck.
0:04:22 > 0:04:24There's its ears, that's an eye,
0:04:24 > 0:04:26and its mouth.
0:04:26 > 0:04:28That's really natural, isn't it?
0:04:28 > 0:04:31And this looks like the giraffe dipping its head down,
0:04:31 > 0:04:34drinking some water - we've got a herd of giraffes here!
0:04:42 > 0:04:45There's two cats.
0:04:45 > 0:04:47They're fighting.
0:04:51 > 0:04:53This... What is this?
0:04:53 > 0:04:57It looks like the figure of a man, but he's wearing a bikini.
0:05:03 > 0:05:07And this is clearly a crocodile, which is especially odd here.
0:05:07 > 0:05:10This is an aquatic animal, it doesn't just paddle around.
0:05:10 > 0:05:13It needs a lot of water to live in. In fact,
0:05:13 > 0:05:17all the creatures are depicted on these rocks are not desert animals -
0:05:17 > 0:05:19they need wet conditions.
0:05:23 > 0:05:27In such a parched wilderness, how can this be?
0:05:30 > 0:05:35The only explanation is that 6,000 years ago, this place was wet.
0:05:42 > 0:05:47Once you know what to look for, the evidence is all around.
0:05:49 > 0:05:53Up there is a river valley that's been carved out into the rock,
0:05:53 > 0:05:55and it's been carved by running water
0:05:55 > 0:05:59which has flowed down here, smoothing off this rock bed,
0:05:59 > 0:06:02and then cascaded down into the valley and off there.
0:06:02 > 0:06:066,000 years ago, that was a big river.
0:06:21 > 0:06:25Satellite images reveal that the river bed I'm standing in
0:06:25 > 0:06:28is just one of a network of past river valleys
0:06:28 > 0:06:31that crisscross the Sahara Desert.
0:06:36 > 0:06:4210,000 years ago, this dry, empty place was entirely different.
0:06:45 > 0:06:49Little is known about the early Saharans who lived here then,
0:06:49 > 0:06:53but we do know that they depended entirely on water.
0:06:56 > 0:06:59Water formed the lakes in which they swam.
0:07:00 > 0:07:04Water nourished the plants which fed the animals they hunted.
0:07:07 > 0:07:11Water filled the clay pots from which they drank.
0:07:16 > 0:07:19But then the climate changed.
0:07:19 > 0:07:25About 5,500 years ago, the Sahara began to dry.
0:07:25 > 0:07:29The rains failed, the rivers shrank, and the lakes dried out.
0:07:30 > 0:07:33For the early Saharan people there was only one option -
0:07:33 > 0:07:38to follow the rains and abandon the desert.
0:07:42 > 0:07:45The fortunes of the early Saharan people
0:07:45 > 0:07:48reveal a universal, timeless truth -
0:07:48 > 0:07:51our fate is inextricably linked to water.
0:07:51 > 0:07:55The problem is, water never stands still.
0:07:55 > 0:07:58It's always on the move across the planet.
0:08:03 > 0:08:05We think of this as a blue planet.
0:08:05 > 0:08:10But while water is abundant, most of it is no use.
0:08:11 > 0:08:17More than 97% of the Earth's water is salty ocean, which we can't drink
0:08:17 > 0:08:19or use to grow crops.
0:08:22 > 0:08:28Less than 3% is fresh water, on which all human life hangs.
0:08:29 > 0:08:33What's more, that tiny fraction is often hard to pin down,
0:08:33 > 0:08:38because fresh water has a life cycle all of its own.
0:08:45 > 0:08:51I'm about to explore that cycle, in all its elusive glory.
0:08:56 > 0:08:59You know, water seems so familiar, doesn't it?
0:08:59 > 0:09:01But to see its remarkable qualities
0:09:01 > 0:09:03you have to go to some extreme lengths.
0:09:05 > 0:09:08(MOTOR CHUGS INTO LIFE)
0:09:08 > 0:09:11(REVVING)
0:09:14 > 0:09:16Here we go...
0:09:16 > 0:09:19Ho-ho! Feel that!
0:09:19 > 0:09:21# WAGNER: Ride Of The Valkyries
0:09:21 > 0:09:23Here we go!
0:09:23 > 0:09:26Oh... Hey-hey! Oh, we're off!
0:09:26 > 0:09:28Oh, my God!
0:09:28 > 0:09:30It's a bit bouncy!
0:09:32 > 0:09:35I shouldn't have had that bacon and eggs this morning.
0:09:41 > 0:09:43O-o-o-h! (LAUGHS)
0:09:46 > 0:09:51The fresh water that we depend on begins its life in the oceans.
0:09:54 > 0:09:58As the sun's rays beat down on the surface of the sea,
0:09:58 > 0:10:02they heat the water molecules until some evaporate.
0:10:03 > 0:10:07It's the start of an extraordinary journey.
0:10:07 > 0:10:10You know, when water evaporates,
0:10:10 > 0:10:13it feels as if it vanishes into thin air.
0:10:13 > 0:10:15But although we barely notice it,
0:10:15 > 0:10:20water molecules are suspended around us all the time.
0:10:22 > 0:10:27It's just that we're only aware of it when they clump together as cloud.
0:10:32 > 0:10:38At any one time, less than 1,000th of the world's fresh water is up here
0:10:38 > 0:10:40in the atmosphere.
0:10:40 > 0:10:45It may not seem much, but this is what spreads water from the seas to the land.
0:10:48 > 0:10:52A water molecule doesn't hang around up here for very long.
0:10:52 > 0:10:55In fact, it spends less time up here in the atmosphere
0:10:55 > 0:10:57than at any other time on its journey -
0:10:57 > 0:10:59a mere nine days
0:10:59 > 0:11:04until the typical water molecule crashes to Earth as rain.
0:11:07 > 0:11:09(THUNDER RUMBLES)
0:11:09 > 0:11:11(BIRD SQUAWKS)
0:11:14 > 0:11:16For most of us, rain is perhaps
0:11:16 > 0:11:19the most familiar stage of the water cycle,
0:11:19 > 0:11:22but notoriously the least reliable.
0:11:23 > 0:11:26As the water falls as rain, it joins a bigger system,
0:11:26 > 0:11:32cascading and carving its way across the land surface as streams and rivers.
0:11:37 > 0:11:39Look at that!
0:11:39 > 0:11:41Water absolutely everywhere!
0:11:43 > 0:11:47Rivers and rain are the part of the water cycle that we depend on.
0:11:48 > 0:11:51Whoo-hoo!
0:11:51 > 0:11:56And yet they're only a tiny proportion of the world's fresh water...
0:11:57 > 0:12:02..a measly 2% of all fresh water on the planet.
0:12:02 > 0:12:05The rest of the Earth's fresh water
0:12:05 > 0:12:08is locked away down there, on the ground.
0:12:08 > 0:12:10Oh... (LAUGHING)
0:12:10 > 0:12:12Oh!
0:12:12 > 0:12:13What a landing!
0:12:14 > 0:12:18The vast majority of it is stored as ice.
0:12:21 > 0:12:24Most of the rest seeps deep into the Earth,
0:12:24 > 0:12:27where it's known as groundwater.
0:12:28 > 0:12:31Hidden away down here
0:12:31 > 0:12:35is the planet's second-largest store of fresh water.
0:12:40 > 0:12:44But in the end, all water arrives back in the oceans,
0:12:44 > 0:12:46and the cycle begins again.
0:12:57 > 0:12:59What that circulation means for us humans
0:12:59 > 0:13:03is that water is a moving target.
0:13:03 > 0:13:08We constantly have to seek it out on its endless cycle and intercept it
0:13:08 > 0:13:11wherever and whenever we can.
0:13:11 > 0:13:13This quest to...
0:13:13 > 0:13:18to pin down water has played a defining role in human history.
0:13:21 > 0:13:24You can trace the impact of our quest for water
0:13:24 > 0:13:28right back to the dawn of civilisation,
0:13:28 > 0:13:30about 12,000 years ago.
0:13:30 > 0:13:33It all began with a big block of ice.
0:13:35 > 0:13:3712,000 years ago,
0:13:37 > 0:13:42much of the northern hemisphere was covered in a single, huge ice sheet.
0:13:48 > 0:13:50And even today you can see its legacy...
0:13:52 > 0:13:54..here in Iceland.
0:13:59 > 0:14:05This glacier is a tiny remnant of that once enormous expanse of ice.
0:14:17 > 0:14:22Ice is like a storage cupboard in the circulation of water around the planet,
0:14:22 > 0:14:27a store into which water can be deposited or withdrawn.
0:14:30 > 0:14:33And it was a shift in the amount of water locked up here
0:14:33 > 0:14:38that was to drive one of the greatest ever transformations of human society.
0:14:41 > 0:14:45Today, the ice sheet here is melting and retreating,
0:14:45 > 0:14:47and releasing this great armada of icebergs.
0:14:47 > 0:14:50But if you go back 12,500 years ago,
0:14:50 > 0:14:53it's a very different story.
0:14:53 > 0:14:56Then the ice was expanding,
0:14:56 > 0:15:00sucking moisture out of the atmosphere in vast quantities
0:15:00 > 0:15:02and locking it away in the ice.
0:15:02 > 0:15:05And the effects of that were felt right across the planet.
0:15:20 > 0:15:23Thousands of kilometres away in the Middle East...
0:15:25 > 0:15:29..it led to a drought which lasted for centuries.
0:15:31 > 0:15:35It had its most profound impact in what would become known
0:15:35 > 0:15:41as the Fertile Crescent, an area famed for its exceptionally rich soil.
0:15:47 > 0:15:51This drought would trigger the start of the defining characteristic
0:15:51 > 0:15:53of human civilisation.
0:15:56 > 0:16:00Back then, every human on the planet was a hunter-gatherer.
0:16:00 > 0:16:05Those living in the Fertile Crescent, the Natufians, thrived on rich pickings
0:16:05 > 0:16:10of fruit and berries, with plenty of deer and ibex to hunt.
0:16:11 > 0:16:16But as the drought took hold, to survive they would have to adapt.
0:16:18 > 0:16:22They came up with two distinct strategies.
0:16:22 > 0:16:26One group developed this, the Harif point,
0:16:26 > 0:16:29a new, state-of-the-art arrowhead
0:16:29 > 0:16:33that allowed them to tackle a drought by hunting more efficiently.
0:16:33 > 0:16:37But a second group came up with something a little bit more subtle.
0:16:37 > 0:16:41Although you wouldn't know it, this is a sickle,
0:16:41 > 0:16:45and it offered a completely new approach to gathering food.
0:16:45 > 0:16:49This small, stone blade represented
0:16:49 > 0:16:54a decision not to chase food, but to stay put and grow it.
0:16:57 > 0:17:00The Harif point did a good job for the hunters.
0:17:02 > 0:17:06But it was the sickle that really changed history.
0:17:07 > 0:17:11In a drought, it's safer to stay close to water,
0:17:11 > 0:17:17but that decision to remain in one place meant planting crops was essential.
0:17:17 > 0:17:19If you go foraging in the forest,
0:17:19 > 0:17:22you can only collect so much food with your bare hands,
0:17:22 > 0:17:26but if you've got one of these, you can harvest fast and furious,
0:17:26 > 0:17:30and for the same amount of effort, you can collect far more food.
0:17:30 > 0:17:32With this simple tool,
0:17:32 > 0:17:36these people had begun the agricultural revolution.
0:17:36 > 0:17:39And the rest, as they say, is history.
0:17:43 > 0:17:47A lack of water and a simple but ingenious response
0:17:47 > 0:17:50led to the birth of civilisation.
0:17:53 > 0:17:57But once farming took hold, it had a profound impact
0:17:57 > 0:17:59on our relationship with water.
0:18:01 > 0:18:04No longer could we simply follow the rains.
0:18:04 > 0:18:09Now people needed regular, reliable sources of water
0:18:09 > 0:18:11to make sure their crops grew.
0:18:13 > 0:18:17So the need for water began to define
0:18:17 > 0:18:19where the first civilisations could flourish.
0:18:21 > 0:18:25That led people to the one stage of the water cycle
0:18:25 > 0:18:28that offers reliable fresh water -
0:18:28 > 0:18:30rivers.
0:18:32 > 0:18:33Across the planet,
0:18:33 > 0:18:36rivers cover a tiny proportion of the Earth's surface,
0:18:36 > 0:18:40but for the first farmers, they became magnets.
0:18:45 > 0:18:48But rivers did more than supply a steady source of water.
0:18:48 > 0:18:52They changed the very character of the civilisations
0:18:52 > 0:18:54that grew up along them,
0:18:54 > 0:18:59influencing everything from politics to social organisation.
0:19:02 > 0:19:07The power of rivers to shape history is graphically illustrated
0:19:07 > 0:19:11by perhaps the greatest of all early civilisations...
0:19:17 > 0:19:19..Ancient Egypt.
0:19:21 > 0:19:24You might think you know the story -
0:19:24 > 0:19:27a mighty civilisation that built the pyramids
0:19:27 > 0:19:31under the autocratic rule of ruthless Pharaohs.
0:19:33 > 0:19:36But if you want to understand what really made Egypt great,
0:19:36 > 0:19:41you have to leave the pyramids and the temples behind...
0:19:44 > 0:19:49..and come here, to a small place that hardly anyone visits.
0:19:49 > 0:19:53You know, at first glance these look like your average, everyday,
0:19:53 > 0:19:562,000-year-old steps.
0:19:58 > 0:20:03But this staircase is what made Ancient Egypt tick.
0:20:03 > 0:20:07You get an idea of its true purpose by the markings on the side wall -
0:20:07 > 0:20:11these grooves were carefully carved into the marble -
0:20:11 > 0:20:15because this was a beautifully simple measuring device.
0:20:15 > 0:20:19And to see what it was measuring, you have to pop round the corner.
0:20:21 > 0:20:23Oh!
0:20:23 > 0:20:24It's all wet!
0:20:27 > 0:20:29And this is it -
0:20:29 > 0:20:31the Nile river.
0:20:31 > 0:20:35That set of steps and markings is a Nilometer.
0:20:35 > 0:20:39It measured the changing level of the river.
0:20:39 > 0:20:43Each year when it flooded, the maximum height that the waters came to
0:20:43 > 0:20:46would directly predict the yield of the crops
0:20:46 > 0:20:49and, with that, the profits that the farmers made.
0:20:52 > 0:20:54It worked because the water of the river
0:20:54 > 0:20:58carried something special within it -
0:20:58 > 0:20:59an almost invisible treasure
0:20:59 > 0:21:04that was the secret of Egypt's economic might.
0:21:05 > 0:21:09What made Egypt great is this stuff -
0:21:09 > 0:21:11silt.
0:21:11 > 0:21:15It's a rich soup of minerals, which...
0:21:15 > 0:21:17It's like an espresso.
0:21:17 > 0:21:21Tiny flecks of rock and minerals that the river picked up
0:21:21 > 0:21:26over its wandering course and swept along with the flow.
0:21:34 > 0:21:36All rivers carry some silt,
0:21:36 > 0:21:39but the Nile has the benefit of starting in Ethiopia,
0:21:39 > 0:21:43where the rock is young and volcanic.
0:21:44 > 0:21:47This forms the richest of silts.
0:21:47 > 0:21:52140 million tonnes of the stuff are carried by the Nile down river
0:21:52 > 0:21:54to Egypt each year.
0:21:54 > 0:21:57Every year, the seasonal flood covered the fields
0:21:57 > 0:22:03and left behind nutrient-rich silt that fertilised the crops.
0:22:03 > 0:22:07The more silt, the more food was produced.
0:22:07 > 0:22:09It was the size of the flood -
0:22:09 > 0:22:14and with it the bounty of silt - that the Nilometer was used to predict.
0:22:16 > 0:22:22So, simply by measuring the height of the Nile, the Egyptians were able
0:22:22 > 0:22:26to forecast food production and, with it, the profits of the farmers.
0:22:28 > 0:22:32Each year, they used this information to set tax levels.
0:22:32 > 0:22:37So the wealth and the might and the splendour of Ancient Egypt
0:22:37 > 0:22:41is all down to a simple twist of geographical fate.
0:22:41 > 0:22:44In fact, Ethiopia itself gets almost no benefit
0:22:44 > 0:22:47from that fertile soil washed from its highlands.
0:22:47 > 0:22:51It's even said that its greatest export is the silt
0:22:51 > 0:22:56that it sends down the Nile, silt that made the Pharaohs rich.
0:22:59 > 0:23:02But the ebb and flow of the Nile
0:23:02 > 0:23:07had more far-reaching implications for the Egyptian people than mere taxes.
0:23:13 > 0:23:18Intriguingly, it may be that where access to water is limited,
0:23:18 > 0:23:20that actually determines
0:23:20 > 0:23:25the way a society is organised and even its use of slavery.
0:23:28 > 0:23:31Where water is in short supply -
0:23:31 > 0:23:34or from a single source, as it is in Egypt -
0:23:34 > 0:23:39then you need a highly structured society to get the best out of it.
0:23:43 > 0:23:46For large-scale irrigation, you need bureaucrats to decide
0:23:46 > 0:23:48where to dig the water channels.
0:23:48 > 0:23:51You need teams of working men - slaves, really -
0:23:51 > 0:23:53to do the actual hard work of digging.
0:23:53 > 0:23:57And once the channels are in place, you need farmers with money enough
0:23:57 > 0:23:59to buy the water it's delivered.
0:23:59 > 0:24:02So right away you've got three tiers of society,
0:24:02 > 0:24:05and I haven't even mentioned the Pharaohs.
0:24:07 > 0:24:11So the rigid, hierarchical structure of Egyptian society
0:24:11 > 0:24:15wasn't just dictated by the Pharaohs.
0:24:15 > 0:24:19It also emerged because the Egyptians had only one water source -
0:24:19 > 0:24:20the Nile.
0:24:26 > 0:24:285,000 years ago,
0:24:28 > 0:24:32it wasn't just the Ancient Egyptians who noticed the value of rivers.
0:24:34 > 0:24:39Other great civilisations were also forming along the banks of rivers.
0:24:40 > 0:24:42In Mesopotamia,
0:24:42 > 0:24:48the Sumerian civilisation flourished between the Tigris and the Euphrates.
0:24:49 > 0:24:55Further east, the Harappan civilisation formed by the Indus.
0:24:57 > 0:25:02And early Chinese civilisations were emerging along the Yellow River.
0:25:06 > 0:25:11But not all early farmers were content to settle by rivers.
0:25:11 > 0:25:13Others learned to exploit new sources of water,
0:25:13 > 0:25:16in the unlikeliest places.
0:25:18 > 0:25:21Like the Sahara Desert, in Libya.
0:25:30 > 0:25:34These are the remains of the ancient city of Garama,
0:25:34 > 0:25:39which about 2,500 years ago was the centre of a powerful empire.
0:25:39 > 0:25:43Today, it's a bit of a maze, but from up here
0:25:43 > 0:25:47you can see the shapes of the buildings, the way the streets interconnect.
0:25:53 > 0:25:57You get a real sense of how this place must have worked in its prime.
0:26:07 > 0:26:09This was the home of the Garamantians...
0:26:11 > 0:26:14..which, for me, are a rather forgotten people.
0:26:14 > 0:26:18They've been eclipsed in the history books by their showy contemporaries,
0:26:18 > 0:26:20the Greeks and the Romans.
0:26:20 > 0:26:26The Garamantians dominated the Sahara Desert for almost 2,000 years.
0:26:26 > 0:26:30They were the society that first brought civilisation to the desert.
0:26:34 > 0:26:38Far from just scraping by in this harsh landscape,
0:26:38 > 0:26:41the Garamantes were flourishing.
0:26:43 > 0:26:46They grew crops such as cereals and grapes.
0:26:46 > 0:26:49They kept horses and pigs.
0:26:49 > 0:26:52Clearly, they needed large amounts of water.
0:26:55 > 0:26:58So where did they find it, here in the middle of the desert?
0:27:02 > 0:27:07Now, this is the key to the Garamantians' incredible success.
0:27:07 > 0:27:11It's vertical holes that are sunk deep into the ground...
0:27:12 > 0:27:18...40 to 50 metres - that's about 150 feet.
0:27:18 > 0:27:20And the purpose of them was pretty simple -
0:27:20 > 0:27:22it was to bring water up from below ground.
0:27:22 > 0:27:26In this environment, it must have seemed like it was almost magic.
0:27:26 > 0:27:30In fact, the Garamantians had discovered groundwater.
0:27:32 > 0:27:36Beneath the surface of the Sahara is a surprising part
0:27:36 > 0:27:38of the great water cycle -
0:27:38 > 0:27:41a massive store of groundwater.
0:27:45 > 0:27:48This is water that has seeped into the ground
0:27:48 > 0:27:52and has collected in porous layers of rock.
0:27:52 > 0:27:54The water came from the period
0:27:54 > 0:28:00thousands of years before, when the Sahara was lush and wet.
0:28:01 > 0:28:06Some of that water percolated into the rocks below and remained there,
0:28:06 > 0:28:09despite the dramatic drying above...
0:28:11 > 0:28:15..until the Garamantes found it.
0:28:15 > 0:28:18You kind of dig them down until you hit the water table
0:28:18 > 0:28:20and then you just keep doing the same thing.
0:28:20 > 0:28:25There's one after another, after another, all in a whole line.
0:28:26 > 0:28:30But these holes aren't wells - they're maintenance shafts.
0:28:30 > 0:28:34They reach down to tunnels which carried the water.
0:28:34 > 0:28:38The point is, right up there at the end is where the water source is,
0:28:38 > 0:28:42so the water flows naturally from the escarpment up there, underground,
0:28:42 > 0:28:45down to the kind of oasis over there.
0:28:45 > 0:28:48Now, that's where the Garamantians' city was.
0:28:48 > 0:28:51What they could have done is they could have dug wells down
0:28:51 > 0:28:56and lifted the water out, but that's a lot of work for very little return.
0:28:56 > 0:28:59Much better to use gravity to channel the water
0:28:59 > 0:29:02in an underground tunnel straight to where they need it.
0:29:03 > 0:29:07That was the Garamantians' real ingenuity.
0:29:11 > 0:29:15The Garamantes had managed to tap the same water
0:29:15 > 0:29:20that the early Saharans had enjoyed thousands of years earlier.
0:29:20 > 0:29:23By mining groundwater, the Garamantians managed
0:29:23 > 0:29:28to turn the clock back on the Sahara - they made the desert bloom again.
0:29:31 > 0:29:34But the human struggle to pin down water
0:29:34 > 0:29:37is forever balanced on a knife edge.
0:29:37 > 0:29:41Get that balance wrong and you pay the price.
0:29:42 > 0:29:48For all their ingenuity, the Garamantes over-exploited their groundwater.
0:29:48 > 0:29:54Eventually it ran out, and so did their civilisation.
0:29:55 > 0:29:58Now all that remains are the bats.
0:29:58 > 0:30:00(SQUEAKING AND FLUTTERING)
0:30:05 > 0:30:10Today, modern Libyans have tapped into this same groundwater supply,
0:30:10 > 0:30:15by using pumps to reach deeper than the Garamantes could.
0:30:15 > 0:30:20But just like their ancient predecessors, they're exploiting a finite resource.
0:30:20 > 0:30:24At most, it will last only another 50 years.
0:30:27 > 0:30:31But water in this most inaccessible stage of the water cycle
0:30:31 > 0:30:33is found in many other places.
0:30:35 > 0:30:39It's at its most spectacular in Tallahassee, in Florida.
0:30:41 > 0:30:47Here, divers are just beginning to explore a mysterious series of caves
0:30:47 > 0:30:53called a karst system, carved out by groundwater over millions of years.
0:30:56 > 0:31:00This is one of the planet's least known frontiers.
0:31:01 > 0:31:04When they began, these divers had no idea
0:31:04 > 0:31:06of the extent of the cave network.
0:31:09 > 0:31:14To explore these caves, they've made the longest dives in history,
0:31:14 > 0:31:17travelling more than ten kilometres from the cave entrance.
0:31:20 > 0:31:25They're sometimes underwater for 24 hours at a time.
0:31:30 > 0:31:32Their efforts have revealed
0:31:32 > 0:31:36one of the world's largest underwater cave systems.
0:31:37 > 0:31:42It's part of a huge store of groundwater, of varying depths,
0:31:42 > 0:31:47that underlies all of Florida and reaches into neighbouring states.
0:31:47 > 0:31:50And it's not just the USA.
0:31:50 > 0:31:55There's groundwater in the most unexpected places.
0:31:55 > 0:31:59More than 30% of all the fresh water on Earth is under our feet.
0:32:02 > 0:32:08Looked at this way, our apparently solid planet is more like a sponge.
0:32:16 > 0:32:18In our early history,
0:32:18 > 0:32:23the need for reliable supplies of water led us to rivers and groundwater.
0:32:26 > 0:32:31But as humans spread across the planet, they learned to exploit
0:32:31 > 0:32:35the vagaries of the water cycle in many different ways.
0:32:39 > 0:32:42The key was adaptation.
0:32:43 > 0:32:45(THUNDER RUMBLES)
0:32:46 > 0:32:48Take rain.
0:32:53 > 0:32:57A familiar occurrence in many parts of the world.
0:32:57 > 0:33:01But this is rain at its most extreme -
0:33:01 > 0:33:03the monsoon.
0:33:12 > 0:33:16The significance of the monsoon isn't the human discomfort
0:33:16 > 0:33:20but how the people here have learned to live with it.
0:33:21 > 0:33:24I'm travelling to the very epicentre of the monsoon,
0:33:24 > 0:33:27a place called Cherrapunjee,
0:33:27 > 0:33:32which holds the world record for the highest rainfall in a single year.
0:33:41 > 0:33:44(THUNDER RUMBLES)
0:33:44 > 0:33:47I thought I knew rain.
0:33:47 > 0:33:50If you're from the west of Scotland, you've met rain before,
0:33:50 > 0:33:52but this is different, it's different rain.
0:33:52 > 0:33:55It's hard to explain. It's the sheer intensity of it -
0:33:55 > 0:33:57it just comes barrelling down.
0:33:57 > 0:34:00But also, the raindrops are massive.
0:34:00 > 0:34:03You feel as if you could fill an egg cup with them, which means that,
0:34:03 > 0:34:05within minutes, you're just soaked.
0:34:05 > 0:34:08It's pointless with a hood and all the rest of it - I'm soaked.
0:34:08 > 0:34:11What I really need is a brolly, like this chap.
0:34:12 > 0:34:14Very wet!
0:34:15 > 0:34:16Wet.
0:34:16 > 0:34:18Just watch it, it's very slidy.
0:34:22 > 0:34:26Back in west Scotland, where I'm from, the average annual rainfall
0:34:26 > 0:34:30is nearly a metre, and that might horrify a Californian,
0:34:30 > 0:34:34but here in Cherrapunjee, the annual average rainfall
0:34:34 > 0:34:40is more than ten times that - between 11 and 12 metres.
0:34:40 > 0:34:43That's nearly the height of a four-storey building.
0:34:48 > 0:34:54Streams turn to rivers, and rivers turn to torrents.
0:34:59 > 0:35:03When you live with so much water, you have to adapt...
0:35:03 > 0:35:06just to get around.
0:35:06 > 0:35:10And that's exactly what the local Khasi people have done.
0:35:19 > 0:35:21Look at this!
0:35:21 > 0:35:25Isn't this fantastic? Look at it!
0:35:25 > 0:35:31It's a living bridge - look, you can see all these roots coming down.
0:35:31 > 0:35:33The texture of them is beautiful.
0:35:40 > 0:35:44I mean, this entire structure is built of growing rubber tree.
0:35:50 > 0:35:51It's just mad when you follow it!
0:35:54 > 0:35:57You can see that this is the perfect union of the tree and the villagers.
0:35:57 > 0:36:00The locals have kind of trained the roots,
0:36:00 > 0:36:03kind of guided them through, knitted them together.
0:36:06 > 0:36:09What they've done here is they've grabbed some rootlets like this
0:36:09 > 0:36:12and taken it round. And look, here it is...
0:36:12 > 0:36:15this set of rootlets here. That's incredibly strong.
0:36:15 > 0:36:17It's an anchor for the bridge.
0:36:19 > 0:36:24Ordinary bridges would rot under the relentless drenching of the monsoon.
0:36:24 > 0:36:29What's clever about these root bridges is they get stronger as they get older.
0:36:29 > 0:36:34So wide! I mean, a whole village could get through here.
0:36:35 > 0:36:37(THUNDER RUMBLES)
0:36:44 > 0:36:48Surprisingly, the intensity of the monsoon rain is all down
0:36:48 > 0:36:50to a basic property of water.
0:36:55 > 0:37:00Compared to other substances, water takes a lot of energy to heat up.
0:37:04 > 0:37:07So the land and the ocean react very differently
0:37:07 > 0:37:10to the rising temperatures of early summer.
0:37:13 > 0:37:17During these months, India's land surface heats up much more
0:37:17 > 0:37:19than the surrounding Indian Ocean.
0:37:21 > 0:37:25The high temperature reduces the density of the air,
0:37:25 > 0:37:28creating low pressure.
0:37:28 > 0:37:32That sucks moist ocean air onto the land,
0:37:32 > 0:37:34which brings rain.
0:37:38 > 0:37:41It's because the whole system is driven by the sun's heat
0:37:41 > 0:37:43that the rains come in the summer.
0:37:46 > 0:37:48But it also means that the monsoon
0:37:48 > 0:37:52only lasts for three months of the year.
0:37:52 > 0:37:56For the rest of the time, there's virtually no rain.
0:37:58 > 0:38:00(TRAIN HOOTER BLARES)
0:38:04 > 0:38:07The people of India have adapted,
0:38:07 > 0:38:10as much as they can, to these extremes of the monsoon.
0:38:11 > 0:38:13I think it's this way.
0:38:13 > 0:38:16It's great, you have to use your elbows in here.
0:38:22 > 0:38:26But outsiders are not always so sensitive to its rhythms.
0:38:31 > 0:38:35Here in India, the changing strength of the monsoon year on year
0:38:35 > 0:38:40had really tremendous impacts on the country's political fortunes.
0:38:40 > 0:38:44That's especially true of its recent colonial past,
0:38:44 > 0:38:45the story of which was played out
0:38:45 > 0:38:49against a backdrop of water abundance and scarcity.
0:38:49 > 0:38:52Clearly there are lots of reasons to explain the fate
0:38:52 > 0:38:54of British colonial rule in India,
0:38:54 > 0:38:59but one of the least explored and most intriguing is water.
0:39:02 > 0:39:05In the 19th century, the failure of the British
0:39:05 > 0:39:10to manage India's water supply had significant consequences...
0:39:10 > 0:39:12for them and for the Indian people.
0:39:21 > 0:39:25Perhaps it was naivety, perhaps it was because they were outsiders,
0:39:25 > 0:39:29perhaps it was their inability to cope with extreme weather,
0:39:29 > 0:39:33but the British never really got to grips with the monsoon.
0:39:38 > 0:39:41For thousands of years, people here have been developing ways
0:39:41 > 0:39:43to deal with the monsoon.
0:39:43 > 0:39:47And this was one of the most important - it's a huge open well
0:39:47 > 0:39:51that was dug down deep enough to reach groundwater.
0:39:51 > 0:39:56When the rains came, the water was filtered through the surrounding ground
0:39:56 > 0:40:00and held in the well like a gigantic bucket.
0:40:00 > 0:40:03But these stepwells, as they were known,
0:40:03 > 0:40:05were more than water collectors.
0:40:05 > 0:40:09The genius of this design was it turned the mundane need for water
0:40:09 > 0:40:11into a social ritual.
0:40:11 > 0:40:16People didn't just come here to dip for water - they gossiped,
0:40:16 > 0:40:18they bathed, they even worshipped.
0:40:22 > 0:40:27Over 3,000 stepwells were built, up until the 19th century.
0:40:28 > 0:40:31For millions, they were the main source of water.
0:40:36 > 0:40:39Despite the fact that structures like this helped the Indian people
0:40:39 > 0:40:42survive droughts, the British didn't like it.
0:40:42 > 0:40:47They were concerned that people bathing in the same water they drank from was bad news.
0:40:47 > 0:40:50So on health grounds, they shut them down.
0:40:50 > 0:40:52I mean, they may have had a point,
0:40:52 > 0:40:56and they solved that issue by bringing in piped water,
0:40:56 > 0:40:58but at the same time, they imported another problem
0:40:58 > 0:41:00that was much, much worse.
0:41:03 > 0:41:04It's a little-known fact,
0:41:04 > 0:41:08but the British built canals on a colossal scale across India,
0:41:08 > 0:41:11more than 57,000 kilometres of them -
0:41:11 > 0:41:15perhaps their biggest engineering achievement anywhere.
0:41:18 > 0:41:22Yet the British didn't realise that, even more than stepwells,
0:41:22 > 0:41:26these huge bodies of standing water were a health hazard -
0:41:26 > 0:41:31the perfect environment for malaria to breed and spread.
0:41:36 > 0:41:40Given the lack of sensitivity the British showed to the Indian climate,
0:41:40 > 0:41:45it's perhaps ironic that the monsoon played a significant role
0:41:45 > 0:41:48in undermining British rule in India.
0:41:55 > 0:41:59At the end of the 19th century, the monsoon rains failed.
0:42:04 > 0:42:08For a decade, there were repeated droughts.
0:42:08 > 0:42:11Crops were ruined, and there were terrible famines.
0:42:13 > 0:42:17But the British failed to respond effectively -
0:42:17 > 0:42:21in fact, they even continued to export rice.
0:42:21 > 0:42:26This indifference to the rhythms of the monsoon fuelled popular anger
0:42:26 > 0:42:31against colonial rule, and the independence movement grew rapidly.
0:42:40 > 0:42:42Today, the stepwells are being repaired.
0:42:45 > 0:42:48Pumps accessing groundwater are used to protect
0:42:48 > 0:42:50against the unreliable monsoon.
0:42:52 > 0:42:57And that's made India the largest user of groundwater in the world.
0:43:06 > 0:43:10Adapting to the water cycle has meant the difference between success
0:43:10 > 0:43:13and failure for many civilisations.
0:43:18 > 0:43:22But there was another strategy that also brought success...
0:43:23 > 0:43:27..and that was to take control of the water cycle.
0:43:33 > 0:43:37There was one early civilisation above all others that took control
0:43:37 > 0:43:41of the planet's most dramatically changing source of water.
0:43:42 > 0:43:45They mastered the monsoon.
0:43:50 > 0:43:52They were the Khmers,
0:43:52 > 0:43:55and from the 9th century, they dominated the area
0:43:55 > 0:43:58we now know as Cambodia.
0:43:58 > 0:44:01And this was their greatest achievement...
0:44:01 > 0:44:05the legendary temple complex of Angkor.
0:44:12 > 0:44:15You get a real sense of the age of this place here,
0:44:15 > 0:44:18cos this was built over 1,200 years ago.
0:44:20 > 0:44:23In a few places, like here, you can see it's showing the age.
0:44:23 > 0:44:26Look, the faces have all gone,
0:44:26 > 0:44:31but, look at this, that looks as if it could have been carved just yesterday.
0:44:35 > 0:44:37(THUNDER CRASHES)
0:44:41 > 0:44:43Angkor was built to honour the Hindu gods
0:44:43 > 0:44:47and it symbolised the extraordinary success of the Khmers.
0:44:52 > 0:44:55In a way, this place is a monument to something else -
0:44:55 > 0:45:00the Khmers' ability to harness the power of the monsoon.
0:45:10 > 0:45:13The Khmers were first drawn to this region
0:45:13 > 0:45:17by the Tonle Sap lake and the river that feeds it.
0:45:20 > 0:45:25Today, it's home to a floating, permanent community,
0:45:25 > 0:45:27replete with all the necessary amenities.
0:45:35 > 0:45:37All life here is lived on the river -
0:45:37 > 0:45:43the whole village, houses, shops, churches, schools, everything.
0:45:46 > 0:45:49A hardware store!
0:45:53 > 0:45:57Everybody's watching telly. They're all watching soap operas,
0:45:57 > 0:45:58or just chilling out.
0:46:00 > 0:46:03People settle here today for the same reason
0:46:03 > 0:46:06the Khmers did over 1,000 years ago -
0:46:06 > 0:46:11the unusual behaviour of the lake around monsoon time.
0:46:11 > 0:46:15Each year when the monsoon rains fall, the land around here
0:46:15 > 0:46:21just can't drain fast enough, and this lake, Tonle Sap, swells enormously.
0:46:21 > 0:46:26It more than trebles in size, becoming, for just a few months,
0:46:26 > 0:46:30the largest freshwater lake in Southeast Asia.
0:46:37 > 0:46:42And every year, the water brings with it a spectacular bounty.
0:46:47 > 0:46:52Fish! Loads of them, nibbling away at your toes in this murky water.
0:46:56 > 0:46:59So many, that when it floods, the Tonle Sap lake
0:46:59 > 0:47:02becomes the richest source of freshwater fish in the world.
0:47:06 > 0:47:09Back in the 9th century, the Khmers realised
0:47:09 > 0:47:14that this annual influx of fish and water offered a glittering opportunity.
0:47:18 > 0:47:22They set about building a fishing industry here, and with the profits,
0:47:22 > 0:47:25they built the temples of Angkor.
0:47:28 > 0:47:32But as it grew, the Khmer kingdom faced a stumbling block.
0:47:34 > 0:47:39When the monsoon finished each year, the fish and water would vanish.
0:47:39 > 0:47:44So each year, the inhabitants were plunged into drought and hunger.
0:47:44 > 0:47:47The Khmer rose to the challenge magnificently.
0:47:47 > 0:47:52They decided that rather than be at the whim of the monsoon,
0:47:52 > 0:47:54they would make it work for them.
0:48:10 > 0:48:12This is part of a vast network
0:48:12 > 0:48:15of irrigation tunnels that crisscross the whole of Angkor.
0:48:15 > 0:48:19When the Khmer started digging these in the 9th century,
0:48:19 > 0:48:21people had seen nothing like them.
0:48:21 > 0:48:24This was plumbing on a grand scale.
0:48:34 > 0:48:37From the air, it's still visible today.
0:48:40 > 0:48:44Over 1,000 years ago, the Khmers managed to divert a river
0:48:44 > 0:48:46by 80 kilometres.
0:48:48 > 0:48:50They built canals
0:48:50 > 0:48:55that extended over an area of 1,000 square kilometres
0:48:55 > 0:48:56and dug reservoirs
0:48:56 > 0:49:01that could hold up to 600 million cubic metres of monsoon water.
0:49:04 > 0:49:09With this system, the Khmers seized control of the planet's water cycle.
0:49:09 > 0:49:13They turned the seasonal rainfall of the monsoon into a reliable,
0:49:13 > 0:49:16all-year-round water supply.
0:49:18 > 0:49:23It was an enormous achievement, enabling Angkor at its peak
0:49:23 > 0:49:26to support a population in excess of one million.
0:49:31 > 0:49:34Thanks to their control of water,
0:49:34 > 0:49:39the Khmers had built the largest pre-industrial city in the world.
0:49:50 > 0:49:53The Khmer hung on until the 15th century,
0:49:53 > 0:49:57which was when the kingdom of Angkor finally went to the wall.
0:49:57 > 0:49:59They were victims of their own success.
0:49:59 > 0:50:02Their population went through the roof,
0:50:02 > 0:50:06and they simply outstripped their resources, including -
0:50:06 > 0:50:09despite all that incredible engineering -
0:50:09 > 0:50:11including the water supply.
0:50:11 > 0:50:13I guess that there are limits
0:50:13 > 0:50:16to what even the mighty monsoon can sustain.
0:50:25 > 0:50:28Today, we control water on a massive scale.
0:50:32 > 0:50:39The world's reservoirs now hold over 10,000 cubic kilometres of water.
0:50:39 > 0:50:44That's five times as much water as in all the rivers on Earth.
0:50:46 > 0:50:51And because most of it is pooled in the more populated northern hemisphere,
0:50:51 > 0:50:55away from the equator, the extra weight has slightly changed how the Earth
0:50:55 > 0:50:56spins on its axis.
0:50:56 > 0:50:59It's caused the Earth's rotation to speed up,
0:50:59 > 0:51:05shortening the day by 8 millionths of a second in the last 40 years.
0:51:13 > 0:51:17Today, we take our control of water for granted.
0:51:17 > 0:51:21Modern civilisation couldn't exist without it.
0:51:22 > 0:51:27But there's still only a finite amount of water to go around.
0:51:27 > 0:51:30In many parts of the world,
0:51:30 > 0:51:35scarcity has led to a bitter struggle for control over the available supply.
0:51:35 > 0:51:39And that's true in even the wealthiest countries.
0:51:40 > 0:51:45Today, Los Angeles is a city with every luxury and convenience.
0:51:51 > 0:51:54Yet not so long ago, at the turn of the last century,
0:51:54 > 0:51:57Los Angeles was struggling.
0:51:58 > 0:52:03LA's problem was its location, hemmed in on three sides by desert
0:52:03 > 0:52:06and on the fourth by ocean.
0:52:06 > 0:52:10So it lacked the most basic requirement for city life -
0:52:10 > 0:52:12a reliable water supply.
0:52:15 > 0:52:19So it came up with a plan to get the water it so needed.
0:52:26 > 0:52:29400 kilometres to the north of the growing city,
0:52:29 > 0:52:32nestled within the Sierra Nevada mountain range,
0:52:32 > 0:52:35was a place called Owens Valley.
0:52:36 > 0:52:41It was a verdant place, where people were settling and building farms.
0:52:41 > 0:52:45At the heart of it was plentiful water -
0:52:45 > 0:52:48a wide river feeding a huge lake.
0:52:53 > 0:52:57This valley must have seemed like the answer to Los Angeles' prayers.
0:52:57 > 0:53:00There was enough water here to easily supply
0:53:00 > 0:53:02over one million people.
0:53:02 > 0:53:04There was only one problem...
0:53:04 > 0:53:06it didn't belong to them.
0:53:06 > 0:53:10It belonged to the farmers of Owens Valley.
0:53:10 > 0:53:12It would have to be taken by stealth.
0:53:23 > 0:53:25It wasn't long before men appeared in the valley,
0:53:25 > 0:53:28masquerading as investors.
0:53:29 > 0:53:34They offered to buy up farmland at seemingly irresistible prices,
0:53:34 > 0:53:37just to get the water rights that went with it.
0:53:39 > 0:53:43It wasn't technically illegal, but it was certainly shady.
0:53:44 > 0:53:46And it worked.
0:53:46 > 0:53:50In 1913, after six years of construction,
0:53:50 > 0:53:51an aqueduct was opened.
0:53:51 > 0:53:53And this is it.
0:54:06 > 0:54:09In a way, this aqueduct was a triumph,
0:54:09 > 0:54:12certainly as far as Los Angeles was concerned.
0:54:12 > 0:54:15It allowed millions of people 200 miles down there
0:54:15 > 0:54:18to live in a growing and vibrant city.
0:54:18 > 0:54:21But that's not how people here saw it.
0:54:22 > 0:54:26The Owens Valley farmers didn't give up without a struggle.
0:54:29 > 0:54:31A kind of loose resistance movement started,
0:54:31 > 0:54:35and they would take over places like this and open the sluice gates,
0:54:35 > 0:54:38allowing the water to pour back down into Owens Valley.
0:54:38 > 0:54:42And regularly they'd dynamite the aqueduct.
0:54:44 > 0:54:46But the city rebuilt it,
0:54:46 > 0:54:49and a game of cat and mouse continued
0:54:49 > 0:54:52for three more dynamite-filled years.
0:54:52 > 0:54:57Eventually, the police clamped down with a "shoot to kill" policy,
0:54:57 > 0:54:59and the rebellion fizzled out.
0:54:59 > 0:55:02The city had won.
0:55:06 > 0:55:11Today, the Los Angeles Aqueduct is just part of a giant network
0:55:11 > 0:55:16of pipes and aqueducts all serving one of the world's great cities.
0:55:35 > 0:55:38But, back in Owens Valley, the lake has all but vanished,
0:55:38 > 0:55:41and the river is barely a trickle.
0:55:43 > 0:55:48The story of Owens Valley is not an isolated case.
0:55:48 > 0:55:52Today, there are conflicts over water taking place all around the world.
0:55:57 > 0:56:00Israel, the Palestinians, Syria and Jordan
0:56:00 > 0:56:03dispute access to the River Jordan.
0:56:05 > 0:56:10Egypt, Sudan and Ethiopia quarrel over the waters of the Nile.
0:56:13 > 0:56:16On the Indus river,
0:56:16 > 0:56:21India and Pakistan are in conflict over dams built on the river's tributaries.
0:56:21 > 0:56:24And these are only some of the more well-known examples.
0:56:28 > 0:56:3210,000 years ago, we lived at the whim
0:56:32 > 0:56:35of the unpredictable water cycle.
0:56:37 > 0:56:41Since then, we have harnessed the power of rivers
0:56:41 > 0:56:43to advance our civilisations.
0:56:47 > 0:56:50We have extracted groundwater from the depths
0:56:50 > 0:56:52of the most unlikely places.
0:56:54 > 0:56:59And we have learned to redirect and store water on a massive scale.
0:57:05 > 0:57:10Today, we have unprecedented power over the planet's water.
0:57:11 > 0:57:14But one thing hasn't changed -
0:57:14 > 0:57:18there's still only a finite amount of water on Earth.
0:57:26 > 0:57:27It seems to me
0:57:27 > 0:57:31that water is the Achilles heel of our modern civilisation.
0:57:31 > 0:57:33It's the one resource,
0:57:33 > 0:57:34more than any other,
0:57:34 > 0:57:37with the potential to limit our ambitions.
0:57:39 > 0:57:43The fundamental limits of the water cycle are still there.
0:57:43 > 0:57:48But the lesson of history is that the most successful civilisations
0:57:48 > 0:57:50learn to adapt to those limits.
0:57:52 > 0:57:55So the problem is more with us.
0:57:55 > 0:58:00Now, that prospect may find you gloomy or, like me, more optimistic.
0:58:00 > 0:58:05But either way, at least the future's in our hands.
0:58:08 > 0:58:10Next time, wind. For thousands of years,
0:58:10 > 0:58:13the wind has shaped the destiny of people
0:58:13 > 0:58:16across the planet.
0:58:16 > 0:58:18It's made fortunes
0:58:18 > 0:58:20and brought ruin.
0:58:20 > 0:58:25Even today, we're still at its mercy.