Lesson video

Hello, my name's Miss Gilyeat, and I'm going to be our geography teacher for today.

In today's lesson, we are starting the Rivers: How Do Rivers Shape the Land unit.

And our lesson is about the hydrological cycle, okay? So let's get started.

So your lesson outcome for today is that you can describe the hydrological cycle, including the major stores of water and the movement between them.

We've got four keywords for today's lesson.

So the first one is hydrological cycle, which is the continuous movement of water between the ocean, land, rivers, and atmosphere.

Our second keyword is transfers.

So this is the way that water moves between the different stores within a cycle.

The third keyword is stores, where water is stored within the hydrological cycle.

The fourth keyword is atmosphere, which is the layer of gases that surround the earth.

Now these keywords are highlighted in bold throughout the lesson to help you out.

Okay, so we've got two learning cycles.

So first of all, we're gonna learn about the global hydrological cycle, and then we're gonna learn about the local hydrological cycle, okay? So the hydrological cycle is a continuous movement of water around the planet through various stages.

Gravity and solar energy drive the cycle.

So I want you to think, how do you think gravity and solar energy may drive the system? So that means how they get them to work.

So what does gravity and solar energy do, which means that water can move around our planet? Okay, so we've got two answers here from Jun and Sofia.

So Sofia says, "Gravity is a force which drives things to the centre of the Earth.

Therefore, for the water cycle, gravity cause water to go downhill." So well done, Sofia.

Okay, and for Jun, so solar energy heats up the Earth.

The sun's energy allows water to evaporate and therefore move from the surface of the Earth to the atmosphere.

Well done, Jun.

Now the global hydrological cycle is a closed system.

This means that no new water enters the system, but also, no water leaves it.

Water is constantly being moved in a cycle.

So all of the water that you use on a daily basis, that is not new water.

It has been here on Earth for millions of years, but it is being constantly cycled round.

Okay, true or false.

The global hydrological cycle is an open system.

That's false.

Can you tell me why? It's a closed system as no water enters or leaves the system.

So well done if you got that correct.

Now, a store of water is where water can be kept or stored on Earth.

So imagine a bucket of water.

So where on our planet do you think water is stored? Where is it kept? Have a quick chat with your partner.

Now, water can be stored in different places.

So it can be stored in the oceans, in ice caps and glaciers, on land.

So that could be above the land's surface or underground.

And a small amount is stored within the atmosphere.

Now the amount of water in the different stores can change, but the current distribution is this.

So 97% of Earth's water is in the ocean.

So that's the vast majority of the water that we've got on Earth is in the ocean.

Ice caps and glaciers hold about 2.

1%.

Land holds about 0.

9%.

So that's above and below ground.

And the atmosphere has 0.

001%.

So a very small amount of our water, okay? You might notice from this then that the majority of Earth's water is salty, okay? Because it's stored in the oceans.

And that actually means there's only a very small percentage of the Earth's water that we can use for things like drinking, growing crops, cooking, cleaning, et cetera, okay? So that's the 0.

9% on land, because we can't access the water that's in ice caps either 'cause it's frozen.

Okay, so let's check our understanding.

Where is most water stored on Earth? Oceans, with 97%.

So well done if you got that right.

Okay, so water moves between the ocean, land, ice, and atmosphere through something called a transfer, okay? Now, so a transfer is how basically it gets from one of those stores to the next.

Now, on the slide here, I've got the stores on either side of the the slide, okay? Now, the arrows represent the transfers.

So I want you to think, how could water get from the store on the left to the store on the right, okay? So have a think.

Let's go through them.

So for water in the ocean to get into the atmosphere, it needs to evaporate, okay? So it rises up and it turns, in this process, from a liquid into a gas.

So it turns from water into water vapour, okay? So next one.

How does it then get from the atmosphere to surface water, which is water on the surface of the land, okay? So water on Earth.

How does it do it? Well, that's through precipitation.

So rainfall, snow, hail, any form of precipitation, water in the atmosphere gets back onto Earth.

Again, through this process, it's changed its form now.

So in the atmosphere it's a gas, but when it's on Earth it is a liquid.

Right, next one.

How does water get from ice caps or glaciers to surface water, so such as rivers and lakes? How does it do it? Melting, okay? So warmer temperatures cause ice to melt.

Next one, how does surface water, so water on the surface of the land, rivers, lakes, et cetera, how does that get into the oceans? Through rivers, okay? And that is the whole unit that we are going to be learning about.

So we'll be looking at rivers in a lot more detail later on.

Now, as I just said earlier, the distribution of water on our planet changes over time.

So at the moment, the vast majority, so 97% of our water, is stored in the ocean.

However, that has not always been the case.

So why do you think that the distribution of water in those different stores could change? Have a quick chat with the person that you are sat next to.

Okay, Alex has got an answer for us here.

So if the global climate change, it could change the amount of water stored in ice.

If global temperatures increase, there'll be less water in ice caps and more in the oceans.

So well done, Alex.

Basically, the climate determines how much water you've got in different stores, okay? So if you've got a colder climate, okay, you've got more water stored in ice.

And if the climate gets warmer, then more of that ice melts and it's stored within the oceans, okay? So well done, Alex.

Right then, let's check our understanding.

Which of the following is a transfer within the hydrological cycle? The answer is c, precipitation, because ocean and groundwater are stores, they're not transfers.

Okay, we're on to our first task for the lesson.

So for question one, I'd like to explain why the global hydrological cycle is a closed system.

And question two, put the following words into the correct column of the table of the stores and transfers.

So the words are evaporation, ocean, atmosphere, precipitation, ocean, lakes, rivers, groundwater, and melting, okay? So pause the video and have a go at questions one and two.

Okay, let's check our understanding.

So the global hydrological cycle is a closed system as no new water enters or leaves the system.

So well done if you got that correct.

And for stores, we've got oceans, atmosphere, lake, and groundwater.

Transfers, evaporation, precipitation, rivers, and melting.

So well done if you've got those correct.

Okay, let's get going with our second learning cycle, looking at the local hydrological cycle.

Now the movement of water also happens on a local scale.

So here's a diagram of a hydrological cycle of a drainage basin, right? So it might be worth just pausing the video here and just having a look at the different components of the drainage basin system, just so you kind of get an idea of what's going on, because you will have already understood some of this when we looked at the global scale, because some of the processes, the transfers, and the stores actually are the same.

Now the drainage basin hydrological cycle, or the local hydrological cycle, is an open system.

Water can enter the system, okay? So new water can come in, but water can also leave.

So that's different to the global system because we don't get any new water on Planet Earth and no water leaves.

However, within a drainage basin in a local area, new water can come in and water can leave, okay? So it's an open system.

Let's check our understanding.

The local hydrological cycle is an open system.

True or false? The answer is true.

And can you tell me why? So it's an open system as water enters and leaves the system.

So well done if you got that correct.

Now we're gonna go through this system in a little bit more detail.

So I'm gonna work you through the diagram that we have just looked at.

Now, to start off with, energy from the sun heats the surface of the Earth, okay? So again, we need solar energy to drive this change, or this system, okay? So that's the first thing that happens.

Because of that heat, water evaporates from the ocean and water on the land and turns into gas, water vapour, in the atmosphere.

Warmer temperatures lead to more evaporation, okay? So heat from the sun, that can heat ocean water, but it can also heat surface water.

So water on the land, it can heat water in rivers, in lakes, anywhere on the land surface.

And it can cause that water to change from a liquid into a gas, okay, which is water vapour.

It is then, and entered our atmosphere.

Hotter temperatures lead to more evaporation.

Now, that water vapour will eventually cool down.

And when it does that, it turns back into a liquid.

That process is called condensation.

Now, eventually, over time, that liquid in the atmosphere, it's too heavy to hold itself in the atmosphere anymore.

And when it becomes too heavy, precipitation happens, okay? So precipitation is rain, snow, sleet, or hail.

So it happens when the water droplets become too heavy to stay in the atmosphere, so they fall back down to the surface of the Earth.

Okay, let's check our understanding.

So what is the keyword that has been covered up here? Precipitation.

Well done if you got that correct.

So when precipitation lands on the surface of the Earth, the water droplets can take many different routes, okay? So what do you think could happen to a water droplet that falls onto Earth? Where could it go? Have a quick chat with your partner.

So some of that water will fall on vegetation.

Now, when vegetation catches rainwater, so the water has fallen unto its leaves or its branches, this is known as interception.

So the vegetation has intercepted the rainwater.

Some of this water evaporates straight from the vegetation, and that's known as transpiration.

Now this means that less water reaches the land's surface and the rivers.

Now when you look at flooding later on in this topic, we'll talk about how trees can act as a flood defence, because as vegetation catches water, it means that less gets to the surface of the Earth or the floor and therefore less gets into the river.

So planting trees can be used to reduce the amount of flooding.

So if we have a look at this leaf here, we can see that water has fallen on the leaf and it's been intercepted, okay? Now if water evaporates from the leaf or vegetation, that is known as transpiration.

So it's a bit like evaporation but only from vegetation.

Let's check our understanding.

So which is the keyword here which has been covered up? Interception.

Well done if you got that correct.

Okay.

So some of the water falls onto the surface of the Earth and it flows on either side, either on the surface of the land, so that's known as surface runoff, or it can flow into rivers as well, okay? So both of these forms is water on the land's surface.

Due to gravity, the water will all eventually flow back to the ocean, okay? So all surface water eventually flows back into the ocean, okay? So every river that you can see eventually goes to the same place, the ocean.

So let's check our understanding.

So what is the keyword which has been covered up here? And that is surface runoff.

So well done if you got that correct.

Right then.

Now, so we've got surface water, some of which will flow off into the sea, into the rivers, et cetera.

However, some of that water will actually absorb into the soil.

This is known as infiltration, okay? So I've circled there where the infiltration is on the diagram.

Yeah, so water absorbs into the soil, infiltration.

Now, some water can actually flow within soil, okay? Downhill.

And that's due to gravity as well.

And this is known as throughflow.

Eventually water which is flowing through throughflow will flow back to the river, okay? Eventually due to gravity.

Now some of the water which has infiltrated will actually go even deeper into the bedrock below, and this is known as percolation, okay? So I've circled there where percolation happens in the diagram.

The water can be stored as groundwater or move through the rock, and this is called groundwater flow, okay? So it can get stored in rock underground or it can flow within it, okay? Now you might have been caving, or heard of caving, or seen films or TV shows with caving inside them.

So water underground can form really cool cave systems as the water erodes some of that underground rock, which is really cool, I think.

Okay, so what is the keyword which has been covered up here? Percolation.

Well done if you got that correct.

Let's check our understanding again.

So the keyword describe water absorbing into soil is? Infiltration.

Well done if you got that right.

Okay, we're on to our final task for this lesson.

So the first thing that you need to do is match up the keyword with the definition.

Your second task is I'd like you to fill in the gaps on the diagram with the words in the green box on the right, okay? So do the ones that you're most confident with to start with and then leave the trickiest ones till last.

And finally, I'd like you to answer these three questions.

So question three, explain how the sun and gravity are key drivers in the hydrological cycle.

Question four, why can land that is covered in vegetation lead to less water in the rivers? And question five, what happens to water that infiltrates into the ground? So pause the video and have a go at those questions.

Okay, let's check our understanding.

So evaporation is when water changes from a liquid into a gas.

Transpiration is evaporation from vegetation.

Condensation is when water vapour turns into a liquid.

Infiltration is when water absorbs into the ground.

Surface water is when water is flowing over the land.

And interception is when plants catch water on their leaves.

So well done if you got all of those correct.

Okay, let's have a look at the diagram here.

So at the first stage, we've got evaporation, then you can have precipitation, interception, surface runoff, infiltration, throughflow, percolation, and groundwater storage.

So well done if you've got those correct.

Okay, answers to these questions.

So question three, how the sun and gravity are key drivers in the hydrological cycle.

Well, due to the heat from the sun, water evaporates from the ocean and surface of the Earth and enters the atmosphere.

Gravity means that water that falls to the surface of the Earth will eventually end up back into the ocean.

Now why can land that is covered in vegetation lead there to be less water in the rivers? Well, vegetation collects rainfall on their leaves.

This means that less water reaches land, and therefore less water ends up in the rivers.

And for question five, what happens to water that infiltrates into the ground? Well, water that infiltrates into the ground can either be stored as groundwater or it can flow through the ground back into the ocean through groundwater flow.

So well done if you've got those answers correct.

Here we've got a summary for today's lesson.

Now the hydrological cycle is a continuous movement of water around the planet through various stages.

Gravity and solar energy drive the cycle.

Water can be stored in the oceans, atmosphere, and the land.

Water is transferred between the stores through evaporation, precipitation, and surface runoff.

Energy from the sun moves water between the land and atmosphere.

And gravity means that water that falls to the surface of the Earth will eventually end up back into the ocean.

Now that's it for today's lesson.

Well done.

Good job.

And I'll see you next time.

Bye.