:00:00. > :00:18.This time on Weather World we are the highest point of the UK's is the
:00:19. > :00:23.city, uncovering the secrets of urban weather. And finding out why
:00:24. > :00:27.heatwaves hit cities and those of us who live in them the hardest. We
:00:28. > :00:30.take to the rooftops of London to see just how man-made environment
:00:31. > :00:35.can change the weather forced what are you hoping to achieve in the
:00:36. > :00:39.future? When we do weather forecasts we will give more detailed forecasts
:00:40. > :00:45.so there will be differences between different parts of the city. Also on
:00:46. > :00:54.Weather World: Out of nowhere. A view of mudslides and storms, as we
:00:55. > :00:58.take a meteorological view of the world. Scorching summer in southern
:00:59. > :01:03.Europe and the deadly consequences of wildfires that rage out of
:01:04. > :01:06.control. Watch the birth of a flood as it surges down a dry riverbed to
:01:07. > :01:11.the floods that sweep away everything in their path and the
:01:12. > :01:18.disaster they cause. Plus, cold comfort. The blanket response to
:01:19. > :01:23.melting glaziers in the Austrian alp. Scientists have realised there
:01:24. > :01:27.has an unprecedented glacial melt, so the question now is how serious
:01:28. > :01:45.is that melts and what can they do to stop it? Welcome to Weather World
:01:46. > :01:49.and a view you will never forget. The skyscraper that stands above
:01:50. > :01:52.everything else in London. From up here you can see the haze that
:01:53. > :01:56.stretches over this urban landscape and tells you that the areas
:01:57. > :01:59.different compared to win the countryside. And it is the unique
:02:00. > :02:02.properties of urban air which produces weather and climate
:02:03. > :02:08.differences which in packed everyone who lives and works in a city. It's
:02:09. > :02:13.called the urban heat island effect. That is built up or man-made area
:02:14. > :02:17.that significantly warmer than the surrounding countryside for not it
:02:18. > :02:21.is often most noticeable overnight when the temperature difference can
:02:22. > :02:25.be as much as 12 Celsius between the inner city and the rural
:02:26. > :02:29.surroundings. There are several causes of the urban heat island
:02:30. > :02:33.effect. Firstly, dark surfaces and the types of materials used in
:02:34. > :02:38.cities, like concrete and tarmac, tends to absorb more solar radiation
:02:39. > :02:42.on the day and heat up quicker than the countryside. This heat is then
:02:43. > :02:46.released into the city air, creating the warming effect. With high levels
:02:47. > :02:50.of pollutants in the cities, that air is more capable of holding onto
:02:51. > :02:54.the heat, whereas in the countryside where the air is often clearer more
:02:55. > :02:58.of that he can pass through the atmosphere. There's also a lack of
:02:59. > :03:02.evaporation in cities due to less vegetation and fewer bodies water.
:03:03. > :03:07.In more rural areas this evaporation from trees and water removes heat
:03:08. > :03:11.from the surrounding area. As well as the materials used in cities, the
:03:12. > :03:15.other major contributing factor is the topography of the structure of
:03:16. > :03:19.urban areas. Imagine for instance wind flowing in a relatively
:03:20. > :03:22.straight line across open countryside will stop when that
:03:23. > :03:26.blows across an urban area, the buildings create more friction to
:03:27. > :03:31.the flow, aching it slow and more to be learned. This in turn reduces its
:03:32. > :03:35.capacity to disperse heat. So with more than half the world's
:03:36. > :03:39.population living in urban areas, this heat island effect has a huge
:03:40. > :03:44.impact on our weather and daily lives. We are swapping one high-rise
:03:45. > :03:49.for another, as we cross the city from south to north, joining a team
:03:50. > :03:53.of investigating urban weather. What they are discovering could one-day
:03:54. > :03:56.narrow down weather forecast from hold to parts of the city and
:03:57. > :04:02.perhaps even individuals reads. Behind me you can see the Shard on
:04:03. > :04:05.the London skyline and it is part of the research project here where
:04:06. > :04:08.various pieces of meteorological equipment are taking readings of
:04:09. > :04:13.different elements of the weather. One of those pieces of equipment is
:04:14. > :04:17.inside the silver box and that's a thermal imaging infrared camera.
:04:18. > :04:22.This camera is looking down at the city and is taking measurements of
:04:23. > :04:25.temperature coming of different materials, like buildings, roads and
:04:26. > :04:28.vegetation. To tell us more about this camera and what is its
:04:29. > :04:36.measuring the going to meet a Ph.D. Is due to end. Talk me through this
:04:37. > :04:41.camera. -- student. What is enjoying us? This infrared camera is
:04:42. > :04:45.sensitive to radiation which can be used to determine surface
:04:46. > :04:49.temperatures. If I was to point the camera at different surfaces, like
:04:50. > :04:54.my hand, surfaces of different to bridge will appear a different
:04:55. > :04:57.colour? Yes, this is a thermal graph of the temperatures which you can
:04:58. > :05:01.see through the camera. Your hand is appearing cooler than the
:05:02. > :05:04.surroundings. The different colours represent different temperatures.
:05:05. > :05:13.Have a look at how this works down the city. You've got several of
:05:14. > :05:17.these infrared cameras positioned at different places around the
:05:18. > :05:21.building. This one here is looking down at some buildings and roads and
:05:22. > :05:25.vegetation down below us. Talk as through what it looks like and what
:05:26. > :05:30.we are seeing on the infrared image. This is a time lapse of imagery. You
:05:31. > :05:33.can see the same principle as with your hand, different colours
:05:34. > :05:38.representing different temperatures. There's variety of colours, meaning
:05:39. > :05:41.the surface and temperatures are highly variable. Why are we
:05:42. > :05:47.interested in these measurements? Typically we use a satellite base of
:05:48. > :05:51.measurements, looking straight down at the surface. That means they have
:05:52. > :05:55.a preferential view of the roof and ground surfaces as opposed to all
:05:56. > :05:59.surfaces. I'm doing a ground proving exercise here, with lots of
:06:00. > :06:04.measurement of different angles. These temperatures are really
:06:05. > :06:07.important for evaluation and input. We will have more from the rooftop
:06:08. > :06:13.later. When the going gets hot, you do what
:06:14. > :06:17.you can to stay cool. It's been a summer of extreme heat in southern
:06:18. > :06:23.Europe. Temperatures soaring well into the 40s Celsius from Spain,
:06:24. > :06:29.across to the Balkans. In Italy, the heat exacerbated drowned. The pope
:06:30. > :06:33.ordered the famous fountains of the Vatican to be turned off to show
:06:34. > :06:38.solidarity with the people of Italy and Rome, where temperatures hit 43
:06:39. > :06:43.Celsius. Hot, dry and now on fire. Wildfires
:06:44. > :06:50.led to thousands being evacuated from campsite here in France, in
:06:51. > :06:57.July, spending the night on beaches as the smoke billowed above them.
:06:58. > :07:01.Portugal, in June. The catastrophic forest fire kills more than 60
:07:02. > :07:07.people. The country's worst disaster for more than 25 years. The majority
:07:08. > :07:11.of people were killed on this road, rapidly engulfed by fire as families
:07:12. > :07:14.already fleeing from their home is where trying to drive to safety.
:07:15. > :07:20.More fire, but a different continent. This is South Africa,
:07:21. > :07:24.near Cape Town, in June, as the drought combined with strong winds
:07:25. > :07:29.spread wildfire sparked by lightning. They followed a major
:07:30. > :07:35.storm that inundated the coastline here, with high seas and big waves.
:07:36. > :07:41.The South African weather service said was the worst winter storm here
:07:42. > :07:46.in 30 years. Big storms have hit Europe too. This is Moscow, in May.
:07:47. > :07:52.A severe thunderstorm, the worst in a century, killed 16 people,
:07:53. > :07:57.toppling trees, with winds of up to 70 mph. And astonishing scenes from
:07:58. > :08:03.Poland, in August, as storms bring down tens of thousands of trees,
:08:04. > :08:07.killing six people. It was declared the worst disaster of polish and
:08:08. > :08:11.possibly European forest history. Storms brought devastating
:08:12. > :08:17.downpours. Turkey, Istanbul, in July. Roads turn to readers. There
:08:18. > :08:22.have been a number of flooding Storms in the city this dud summer.
:08:23. > :08:27.In the UK storms followed a hot start. This was Cornwall in July.
:08:28. > :08:32.The torrential rain and hail lasted over an hour, causing a flash flood
:08:33. > :08:36.to sweep through the village, taking everything it could carry towards
:08:37. > :08:39.the sea. This woman found her elderly mother's walking frame
:08:40. > :08:45.amongst the piles of debris and next to it even her kitchen sink. It's
:08:46. > :08:50.happened. You can't put it back. You just have to get on and carry on and
:08:51. > :08:57.do what we can. We'll get back to normal. We're Cornish! Earlier in
:08:58. > :09:03.the summer heatwave provoke an unusual protest at a Devon school.
:09:04. > :09:06.Boys were told they couldn't wear shorts, because it wasn't official
:09:07. > :09:13.uniform. So they wore a skirt instead. They can't stop us doing
:09:14. > :09:18.it. Girls are allowed to wear skirts. They get cold legs and we
:09:19. > :09:21.have to sit there sweating! The school says as hot weather becomes
:09:22. > :09:27.more common, it may consider a change. Protest is real!
:09:28. > :09:31.We are back at our urban experiment on the rooftop in London. Earlier,
:09:32. > :09:38.we saw thermal imaging to look at how different surfaces, grass,
:09:39. > :09:42.concrete, humans, heat and release the heat at different levels. That's
:09:43. > :09:45.enough of that. That's really important because those different
:09:46. > :09:49.surfaces are also heating the air above them at different levels.
:09:50. > :09:54.Different writing of that air. That goes on to affect the air around us
:09:55. > :10:00.and also the weather. Ben Crawford is monitoring how much the air
:10:01. > :10:05.moving around -- how much the air is moving around us. This measures wind
:10:06. > :10:09.speeds in three dimensions. With this piece of equipment we can
:10:10. > :10:13.measure the cumulative effect of all the different surfaces and their
:10:14. > :10:17.heating of the air. Importantly, I'm filling the air blow right at me
:10:18. > :10:22.sideways, but when you are talking about different surfaces heating the
:10:23. > :10:26.air above, it's rising from ground upwards, which is also measured with
:10:27. > :10:30.this. You would expect that air to be writing differently, depending on
:10:31. > :10:35.where it's come from. Exactly. You can imagine a natural environment
:10:36. > :10:39.like a field or forest and replace that with the city, with glass and
:10:40. > :10:43.concrete and brick, you will change the thermal properties of that and
:10:44. > :10:47.change how the air flows and moves. This is measuring what's going on
:10:48. > :10:53.just here, but you've also got another piece of kit, measuring over
:10:54. > :10:59.a big distance? This measures disturbances from the air, from the
:11:00. > :11:03.heat rising, the military shimmers coming off a hot roof or it piece of
:11:04. > :11:08.concrete. This is pointed across the city towards the foot tower, about
:11:09. > :11:12.four kilometres away. So this really is the invisible world of what's
:11:13. > :11:16.going on in the air right above the cityscape? That's right. With the
:11:17. > :11:20.data from this instrument we can make the invisible visible. Here we
:11:21. > :11:24.have a series of days in the summertime in London and we can see
:11:25. > :11:28.during the mid- day, the hottest part of the day, we have the
:11:29. > :11:32.greatest heat emissions and we can see this rise in the graph.
:11:33. > :11:36.Overnight when the surfaces cool we can see less heat emission coming
:11:37. > :11:40.off the surface. What does it matter? How does knowing about all
:11:41. > :11:44.of this turbulent air possibly improve the weather forecast for the
:11:45. > :11:49.city? That's a good question. It emissions and turbulence affects a
:11:50. > :11:54.lot of things. It affects air cabbage, wind speed, it affects the
:11:55. > :12:00.dispersal of pollutants and can even impact things like clowns. -- air
:12:01. > :12:04.temperatures. We can narrow down the forecast to a smaller part of the
:12:05. > :12:09.city? That's right. We can give a specific forecast for a city, and
:12:10. > :12:12.even perhaps later different neighbourhoods in the city. Thanks
:12:13. > :12:18.for revealing the hidden world on what's going on in the air around
:12:19. > :12:22.us. You're very welcome. Turbulence and updraughts when
:12:23. > :12:26.airborne Our Watch hotair balloons try to avoid. But getting airborne
:12:27. > :12:35.is the problem here. We are trying to get air app. Two balloons collide
:12:36. > :12:38.in June. Swirling winds blow them off course. Luckily what could have
:12:39. > :12:44.ended in tragedy only left one man with minor injuries.
:12:45. > :12:49.Lightning sparks across the south Wales guy in May. The earth's
:12:50. > :12:52.surface is struck about 100 times every second and were never
:12:53. > :12:56.lightning strikes you can be sure BBC Weather Watchers will try to
:12:57. > :13:00.succeed where many of us fail to get a good photo of it. This will all
:13:01. > :13:03.taken when storms swept through the UK in July. Become a BBC Weather
:13:04. > :13:12.Watchers by signing up online. Coming up, how a blanket could help
:13:13. > :13:19.produce a phenomenon known as glacial melt.
:13:20. > :13:22.So far on Weather World we've been getting very high-tech at this open
:13:23. > :13:25.weather experiment on this windy rooftop in London. But along with
:13:26. > :13:30.the high-tech, I found something that's a little bit more familiar,
:13:31. > :13:34.at least to me, which is a weather station. We've seen a lot of these
:13:35. > :13:38.on our travels on Weather World. In Northumberland we saw a fully
:13:39. > :13:43.working weather station there. Insight here we've got a thermometer
:13:44. > :13:48.and it is measuring humidity with this gauge. All inside a very clever
:13:49. > :13:51.box which takes it from the direct sunshine and excessive wind.
:13:52. > :13:54.Of course that weather station had a screen kind which it had a
:13:55. > :13:59.thermometer. Although this isn't the same as that, it similarly protects
:14:00. > :14:08.that the monitor so we can measure the temperature of the air, rather
:14:09. > :14:14.than the sun. And we've also got an anemometer. We've been to the
:14:15. > :14:22.birthplace of these on our travels on Weather World, the Northern --
:14:23. > :14:27.Northern Ireland. It all started here. A simple design. The four cups
:14:28. > :14:32.that spin in the wind and you can measure the wind speed. This
:14:33. > :14:36.anemometer is getting a good workout today, but it's really good to know
:14:37. > :14:39.that wherever we go on Weather World we can find a weather station. But
:14:40. > :14:41.we will get a little bit more high-tech again later in the
:14:42. > :14:42.programme when we come back a time in south-east England. -- but
:14:43. > :14:47.becoming. Engenhao dash-cam technology can now
:14:48. > :14:52.do as a driver's eye view of what it is like to negotiate a flooded road.
:14:53. > :15:01.But things are about to get much worse. -- in-car dash-cam. China and
:15:02. > :15:07.July, and a flash flood after many days of rain leaves many needing
:15:08. > :15:13.rescue. Here, and the injuries, in June, a desperate search for
:15:14. > :15:21.survivors as heavy rain triggers a landslide that kills more than 100
:15:22. > :15:27.people. From Sri Lanka to Nepal, millions are affected. In Nepal, the
:15:28. > :15:33.float is worst in August. Alison is used to rescue people trapped in
:15:34. > :15:40.water. In June, torrential rain in Taiwan. -- elephants use. More 100
:15:41. > :15:46.600 millimetres in six hours. Similar scenes in Japan in July,
:15:47. > :15:54.where rain causes more than half a million people out of their homes.
:15:55. > :16:03.When a flash flood Russia is a major city, disaster strikes. Freetown, in
:16:04. > :16:09.August. And a massive downpour causes muddy water to certain
:16:10. > :16:11.industries. Then a mountainside collapses, bearing whole communities
:16:12. > :16:17.and families as they slept. Hundreds are under this flood, and the death
:16:18. > :16:21.toll may never be known. It is the rainy season here, but this year it
:16:22. > :16:42.has come with unusual and deadly ferocity. And just how quickly can
:16:43. > :16:47.rain transform a trader Rusty weather -- transform a rusty river
:16:48. > :16:52.bed into it a river? A happy surprise to some of the southern
:16:53. > :16:59.hemisphere for winter, as Santiago is hit with snowfall in July. The
:17:00. > :17:03.snowfall caused treacherous driving conditions, not that these motorists
:17:04. > :17:09.seem to care. But unusual cold stats look like local anomalies against a
:17:10. > :17:16.tide of record warned. Alaska. Parts of this US state had its warmest
:17:17. > :17:22.July on record. A council meeting he assigned an agreement accepting the
:17:23. > :17:29.need to tackle climate change. But less than a month later, this. In
:17:30. > :17:39.order to fulfil my solemn duty to protect America and its citizens,
:17:40. > :17:45.the United States will withdraw from the Paris climate accord. Donald
:17:46. > :17:51.Trump's announcement brought international condemnation. The
:17:52. > :17:56.world meteorological association said that in the worst case, it
:17:57. > :18:14.could add 0.3 degrees Celsius to be covered by 2020 three. -- 2022. I'm
:18:15. > :18:18.at the top of this Glazer in the Austrian Alips at about 3,000m high.
:18:19. > :18:38.It is an area very popular for skiing. Actually, there are about 80
:18:39. > :18:47.separate glaciers in this area. -- glacier in the Austrian Alps. This
:18:48. > :18:51.woman is a world renowned glaciologist. She has come up with a
:18:52. > :19:03.surprising answer to our stock, a blanket. On a very small, local
:19:04. > :19:10.scale, we could prevent some very tiny areas. -- protect. But only
:19:11. > :19:14.about 1% of glazier area can be preserved with this method, and of
:19:15. > :19:21.course, it is very cost intensive and needs much labour. -- glacier.
:19:22. > :19:30.To save 1% of a glacier seems futile. But officials say it is
:19:31. > :19:37.worth it. There are 5000 Alpine glaciers in the world. Experts say
:19:38. > :19:41.that half will be gone within only a few years, and those that are left
:19:42. > :19:48.will be much smaller. But it is clear this inexpensive local
:19:49. > :19:51.solution can help on a global scale. Here on the ice sheet, the problem
:19:52. > :19:55.is super-size. There are fears that the melting is happening faster than
:19:56. > :20:00.expected. This is in part due to allergy on the service of the ice.
:20:01. > :20:09.Darker than the ices, it absorbs more of the son of a warmth. --
:20:10. > :20:13.algae. Bevvy as saying that is going to melt in the next decade, next
:20:14. > :20:18.100, or even 1000 years. -- nobody is saying. But it does not need to
:20:19. > :20:24.be completely melted for people to be in danger. Only a small portion
:20:25. > :20:31.is required to raise sea levels, and that threatens coastal communities
:20:32. > :20:38.around the world. And the expansion of renewal, renewable energy is a
:20:39. > :20:43.huge development. -- expression of renewable energy. This is the
:20:44. > :20:47.world's first floating wind farm. So, you have look down towards the
:20:48. > :20:51.ground, and we have seen equipment measured the weather at this level.
:20:52. > :20:57.But now we look into the skies. To do that, I enjoy by Natalie. Talk us
:20:58. > :21:05.through this piece of equipment,. This is a laser that takes a
:21:06. > :21:13.snapshot of the atmosphere. You can't see the laser. It measures
:21:14. > :21:18.outside the vehicle spectrum. So this looks 7000, viz in the sky.
:21:19. > :21:22.What is it measuring? It is measuring reflector from particles
:21:23. > :21:34.in the atmosphere. This could be clad droplets or pollution. -- cloud
:21:35. > :21:39.droplets. So you can get a picture of the clouds and have a picture of
:21:40. > :21:47.how things are at any moment. So now we will talk about the data and how
:21:48. > :21:59.we use it. Sue is an urban climatologist with the university of
:22:00. > :22:05.Redding. -- University of Reading. How is the information useful to
:22:06. > :22:09.you? Is helping us with our weather forecast. But we can also see where
:22:10. > :22:14.clouds form. What we are looking at now is the green is the rural area,
:22:15. > :22:19.and the greater city. You can see the clouds are forming, and what
:22:20. > :22:24.happens to them over cities, and how that is different. We can compare
:22:25. > :22:28.the difference in the real city with what we can see in forecasts like
:22:29. > :22:32.this. So with all the research going on here, had us that tie together,
:22:33. > :22:37.and what are you hoping to achieve in the future? As we think about
:22:38. > :22:41.forecasting into the future, what we are expecting is that models will
:22:42. > :22:45.allow us to look at things in much more detail, so we can look at, for
:22:46. > :22:48.example, the differences between the northern part of the city and the
:22:49. > :22:51.southern part of the city. Hopefully this will make it better for
:22:52. > :22:54.citizens within the city and living in different neighbours. Wonderful.
:22:55. > :23:00.So we're looking at more accurate urban forecasting the future. They
:23:01. > :23:07.you for joining us, Sue, and to all your team, too. Sometimes you need
:23:08. > :23:11.to look of your shoulder to see what the weather is doing. This photo of
:23:12. > :23:14.a man unwilling to abandon me his lawn in Canada in June took certain
:23:15. > :23:18.media by storm. Apparently, the Tornado was further away than it
:23:19. > :23:23.looked. We offers see pictures of the Northern Lines, but these are
:23:24. > :23:29.the southern hemisphere equivalent. It put on a spectacular show in the
:23:30. > :23:33.skies above Australia and New Zealand in May. And finally, the
:23:34. > :23:38.weather can make us all a little hot and bothered in times. Apparently
:23:39. > :23:53.the same goes for gorillas. -- at times. Zola creating a splash at
:23:54. > :23:57.Dallas Zoo. And that is it for this time on Weather World. We will be
:23:58. > :24:07.back later in the year. Until then, keep checking the forecast.