Water is fundamental, it really is the stuff of life.
We know that most of the planet's water sits
in the oceans,
and a tiny fraction of it
– less than 1 in a 1 000 litres of the water
in the Earth's system –
sits on the land.
But that's where we live as well,
so that if we want something to drink,
we don’t need to dig a well,
the water's there.
And it affects every aspect of our lives,
so you would think that we knew where every
last drop of it was,
but we don't.
All of the maps that we've got of the planet's surface,
as far as water is concerned,
are inaccurate in some way and at some time,
because of time,
because they don't include time,
and surface water changes over time.
Rivers migrate, rivers move,
lakes appear and they disappear,
the thing is always changing.
Now,
in a new product that we've created,
called the Global Surface Water Explorer,
we've harnessed the power of 3 million satellite
images that were collected by the United States'
Geological Survey,
and we've used those to produce a set of maps
which we check the accuracy of with 40 000
control points,
so that we've got this immensely accurate map
of the whole planet's surface water.
We can go right down to the level of a single
rice field really.
And the satellite images behind me show how this works.
This is an image of the Karkheh River in Iran,
you can see the river crossing the satellite
image there.
And then a few years later,
when a second satellite image is acquired,
there's a dam has been cut across the river
and the river starts to back up and turn into
a lake. So, what once was a river,
is now a huge lake.
Because this lake is artificial,
we can let water out as well as in,
so even the artificial lakes around the planet
change over time.
The Joint Research Centre,
working with Google's Earth Engine team,
have put the Global Surface Water Explorer available
so it's free to everybody, anywhere, anytime.
