Lesson video

Hello and welcome.

My name is Mr. March, and I'm here today to teach you all about the location and physical characteristics of hot deserts.

So grab everything that you need for today's lesson, and let's get going.

So by the end of today's lesson, you'll be able to describe both the location and the physical characteristics of hot deserts.

Now, we have three key words for today's lesson.

Those are hot deserts, biome, and climate.

Now, hot deserts refer to arid areas experiencing low rainfall, generally below 250 millimetres per year, and extremely high summer temperatures.

A biome refers to a global land area that is characterised by its plants, animals, and climate.

Meanwhile, climate refers to the average weather conditions of a place over a long period of time, typically around 30 years or more.

So we're gonna start with our first learning cycle, which is to identify the location of hot deserts around the world.

Now, a hot desert is a biome characterised by extreme daytime temperatures, often in excess of 40 degrees Celsius, but also a complete lack of precipitation, by which I mean rainfall.

In fact, for it to be classified or defined as a desert, it must receive less than 250 millimetres, which is 25 centimetres, of rainfall per year.

It is these extremely challenging climactic conditions which make it a very difficult environment for plants, animals, and human beings to live in.

So our first learning check.

True or false? Hot deserts receive between 250 and 500 millimetres of rainfall per year.

What I'd like you to do right now is pause the video whilst you make your answer.

Okay.

And here is the correct answer.

The answer is, of course, false.

However, what I'd like you to do once again is pause the video whilst you consider as to why this is false.

So pause the video here.

Okay.

And let's discover as to why this statement was false.

And the reason it's false is because hot deserts receive less than 250 millimetres of rainfall per year.

Really, really well done if you got that correct.

Now, hot deserts are a global and significant biome.

In fact, they cover almost 12% of the Earth's total land area, and there are roughly 30 hot deserts around the world.

Now, I'd like you to consider whether you know any different large deserts.

The one on the screen in front of you is a photograph taken from Uluru in the Great Victorian Desert in Australia, often known as the Australian Outback.

I'd like you to pause the video here whilst you think of any other hot deserts that you know around the world.

So what did you come up with? Well, first of all, hot deserts are generally located between 15 and 30 degrees north and south of the equator, generally near the Tropics of Cancer and Capricorn.

And if we look at this map below on the screen, and we look at the yellow shaded areas, which are indicating our hot deserts, we can immediately pick out that pattern.

Looking at the Tropic of Cancer and Tropic of Capricorn and looking between 15 and 30 degrees south and north of the equator, we see a belt of hot deserts through those lines.

We should also note that the Sahara Desert is the largest hot desert around the globe.

Also, all continents have a hot desert, at least one hot desert, except for Europe and Antarctica.

So here is a learning check.

Which statement most accurately describes the global distribution of hot deserts? I would like you to read through the options and pause the video and make your answer.

Good luck.

Okay, so the correct answer was d, the fact that hot deserts are located between 15 and 30 degrees north and south of the equator.

Really, really well done if you managed to get that answer correct.

My next learning check is for you to select all the continents which have a hot desert.

Once again, pause the video here whilst you make your answer.

Okay, how did you do? Let's find out the correct answers.

So there were five correct answers you were looking for.

And those were a, Africa; c, Asia; e, North America; f, Oceania; and g, South America.

The only two which do not have a hot desert are Antarctica and Europe.

Reason being, of course, these continents are located too far away from the equator and the tropics, therefore making them too cold for a hot desert to exist there.

So really well done if you're able to select those five correct answers.

So practise task.

I would like you now to use an atlas to add the correct name to label each of these five hot deserts that you can see on the map below.

The names you need to use are the Thar Desert, the Atacama desert, the Australian Desert, the Kalahari Desert, and the Mojave Desert.

The second practise task asks you then to focus on describing the location of the Sahara Desert.

I would like you to be sure to refer to lines of latitude, hemispheres, continents, and compass directions in your answer.

And I'm gonna give you a model answer as well to support your own answer when it comes to the Sahara.

Now, Lucas here has answered a description of where the Atacama Desert is located, and this is what he has said.

He says that the Atacama Desert is found in the Southern Hemisphere in Western South America, between the equator and the Tropic of Capricorn.

Now, Lucas's answer is a really good answer.

Why? Because it uses hemispheres, it uses compass directions, it uses continents, and it uses lines of latitude, as noted with the equator and the Tropic of Capricorn there at the end of the answer.

So what I'd like you to do right now is pause the video whilst you answer both practise tasks.

Best of luck.

So let's have a look at the correct answers.

The Mojave Desert is located in North America.

We have the Thar Desert located in Central Asia, between Pakistan and India.

The Atacama Desert is located in Western South America.

The Kalahari Desert is located in the southern tip of Africa.

And finally, the Australian desert is located in Oceania, in the country of Australia.

Second of all, we asked you to describe the location of the Sahara Desert.

Now, your answer may have included the following: the fact that the Sahara Desert is located in the Northern Hemisphere, that it's located in Northern Africa, and finally that it's located between 30 degrees north and 15 degrees north of the equator.

So really, really well done if you were able to get some or all of those correct points in your answer.

So on to our second and final learning cycle.

And this time we're gonna be looking at the physical characteristics of hot deserts.

Now, there are many elements which make up the physical characteristics of hot deserts, and these include the climate, by which I mean the temperature, as well as the precipitation in the area.

Also the soil, thinking about the nutrient quality of the soil, the land forms that are found within a hot desert, and finally, the vegetation.

Now, each of these elements has distinct characteristics in hot deserts.

For example, the climate.

As we already know, the rainfall in a hot desert is below 250 millimetres per year, but also the daytime temperatures can reach as high as 40 or 50 degrees Celsius.

Meanwhile, the nights become extremely cold, sometimes dipping as low as zero degrees Celsius, and sometimes even below that.

The soil in a hot desert can be sandy, can be rocky, or even gravelly.

The key thing which combines all of these different soil types is the fact that the soil is generally of a very poor quality in terms of nutrients, and that it is easily eroded by both wind and water.

Vegetation, needless to say, is very sparse, and it is very highly adapted to the dry conditions, if we think about, for example, vegetation such as cacti.

Finally, landforms. Sand dunes, rock plateaus, and wadis are all found in hot deserts.

So wadi refers to a dry riverbed that may flood during rainfall.

As we can see, hot desert landscapes vary very much.

If we look at the three images in front of you, these are all hot desert landscapes, but you can see that the landscape is very much different in each one.

Nevertheless, the things which determine a hot desert are the climate, its extreme temperatures, but also its extreme lack of precipitation.

And here is a climate graph of Las Vegas in the Mojave Desert in North America to really show you what I mean about the extreme climate in a hot desert.

Remember, with a climate graph, the bars refer to rainfall.

Meanwhile, the line graph refers to the temperature.

When it comes to the bar graph, imagine those blue bars are small glasses being filled up by water.

Whereas with the red line, this indicates temperature.

Let's try and break down the climate graph of Las Vegas a little bit more, starting with the temperature.

If we look at June and July, we can see that there is a peak of 33 degrees Celsius, whereas down in December and January we can see that the temperature dips drastically down to eight degrees.

So certainly in terms of temperature, there seems to be an element of seasonality.

We seem to have warm months during June, July, and August and much colder months between December and February.

Looking forward then to the rainfall, we can see that in the month of February there is a maximum of 30 millimetres.

Whereas again, in those months of June, July, and August, as well as May, there is very little rainfall, indeed.

In fact, if we were to add up all the total precipitation across the year, it's roughly about 125 millimetres, which is well below the 250-millimeter mark, thereby defining it as a hot desert.

Now, my learning check for you is: True or false? It never rains in hot deserts.

So pause the video here whilst you make your answer.

Okay, let's have a look at the correct answer.

Well, the correct answer is, of course, false.

But again, I would like you now to think about why this is false.

So once again, pause the video whilst you consider and make your answer.

Okay, so why is this statement false? Well, it is false because while some deserts are indeed exceptionally dry, a region can experience up to 250 millimetres of rainfall and still be classified as a desert.

Really, really well done if you were able to get those two answers correct.

Now, time for a learning check.

And you need to decide which statement below is correct.

Izzy and Aisha are having a debate about the climate in Las Vegas in the Mojave Desert.

And Izzy says that there are no clear seasons in the Mojave Desert in Las Vegas.

Meanwhile, Aisha says that there are two clear seasons: a dry hot season between May and September and a cooler wetter season between November and February.

Now, what I'd like you to do is look at the climate graph in front of you and decide who you think is correct.

Pause the video here whilst you make your choice.

And the correct answer is Aisha.

Aisha is correct, 'cause clearly, if we look at the climate graph, you will see two clear seasons.

A dry hot season does indeed exist between May and September, and a cooler wetter season does indeed exist between November and February.

Really well done if you got that correct.

Now, why is it that hot deserts experience such extreme heat? Well, it's all to do with their location and the relationship that those areas have with the Sun.

If we look at the diagram in front of you and we compare where hot deserts are located, which we know to be near the equator, at the Tropics of Cancer and Capricorn, we can see how the sun interacts with those areas.

We can see that the Sun's rays hit the Earth at a much more 90-degree angle, head on, at the equator.

This means that the Sun's energy is concentrated on a small area, which makes it extremely hot.

Just for comparison, if you look at how the sun is interacting with the North Pole on this diagram, you can see that due to the Earth's spherical shape, the Earth's energy is spread out over a wider area, causing those areas up at the poles to be colder.

Nevertheless, if we're thinking about our hot desert, the energy from the Sun is concentrated on a smaller area at the lower latitudes, nearer the equator, and therefore makes these areas much, much warmer.

Hot deserts also experience an extreme lack of precipitation.

But why is this? Well, in a way it comes back to the temperature found near the equator.

Let me explain.

So at the equator, warm air rises.

It rises because it is slightly less dense and lighter than the air around it.

The same phenomenon happens with a hot air balloon, which rises because the warm air inside that balloon is slightly lighter than the air outside it.

This means then that the warm air rises.

And as that warm air rises, it cools and condenses, forms clouds, and that moisture is then released back to Earth as rain.

Now, this happens at the equator.

And this is why we find rainforests near the equator and certain tropical regions.

The air, though, is now dry, and it moves away from the equator, and descends, once again, at 20 to 30 degrees latitude.

This diagram gives a good example of what that looks like.

These are known as high-pressure zones, where the air is forcing its way downwards.

This dry air in these high-pressure zones means that clouds and rainfall are extremely rare, simply because there is no moisture in that air that is descending.

Therefore, this is where we see hot deserts being created.

Now, hot deserts, as I said, rarely have clouds.

This lack of cloud blanket lets heat escape, causing nighttime temperatures to decrease dramatically to around zero degrees Celsius.

So a learning check.

Why do nighttime temperatures decrease to around zero degrees Celsius in hot deserts? You have four options.

What I'd like you to do now is pause the video whilst you consider and make your answer.

Okay.

And let's have a look at the correct answer.

The correct answer was b.

The reason why hot deserts get such cold temperatures at night is because of the lack of cloud cover, which allows that heat to escape.

Really well done if you got that correct.

Okay, now on to our final practise tasks.

And this practise task asks you to match the sentence beginning to the sentence end.

So on the left-hand column we have our sentence beginnings, and in the right-hand column you have the sentence endings.

What you need to do is read through and try to match up to complete a correct full sentence.

And for the second practise task, you are being asked to describe the pattern of rainfall in Las Vegas using the climate graph below.

And I've given you a few hints and tips as to what you should include.

Try to include the seasonal pattern of rainfall.

Try to include maximum and minimum amounts.

Can you also try to use a range, by which I mean maximum minus minimum rainfall amounts? Okay, so what I'd like you to do right now is pause the video whilst you write and answer both practise tasks.

Best of luck.

Okay.

So these were the correct answers.

You should have had the fact that hot deserts have two distinct seasons.

You should have said that each year hot deserts receive less than 250 millimetres of precipitation each year.

You should have said hot deserts have very low nighttime temperatures because of the absence of clouds, allowing daytime heat to escape into the atmosphere.

And you should have said high pressure is where air sinks, preventing the creation of rain clouds.

And finally, you should have said hot deserts have high temperatures due to their location near the tropics.

The second and final practise task, where you needed to describe the pattern of rainfall in Las Vegas, your answer could have included some or all of the following.

The seasonal pattern, the fact that there are dry months between May and September, and that there are wetter months between November and February.

You could have mentioned the maximum rainfall in February with 30 millimetres.

You could have mentioned the minimum rainfall in June with roughly two millimetres.

And finally, you could have mentioned the range, equaling 28 millimetres, more or less.

If your answer was perhaps plus or minus one or two millimetres from this, that's okay.

I'm sure you did great.

So really, really well done if you got those answers correct.

So finally, our learning summary.

You need to know that hot deserts receive less than 250 millimetres of precipitation per year.

They're generally located between 15 and 30 degrees north and south of the equator.

It's very hot during the day in hot deserts because of their location close to the equator, meaning that these areas receive intense sunlight.

And finally, it is dry because desert areas are found at high-pressure areas.

So thank you very much for being with me today, and I hope you enjoyed today's lesson.

Thank you and goodbye.