northern areas, potentially 29 or 30 degrees for this evening are largely fine end to the day, rain spreading its way into north—western england and wales, that will move south and east, rain breaking up, cooler and fresher conditions, still pretty warm gci’oss fresher conditions, still pretty warm across the south east, goodbye. hello. this is bbc news with joanna gosling. the headlines: 3000 soldiers are being sent to houston to help residents affected by severe flooding in the wake of hurricane harvey. more than 130 people have been treated in hospital and hundreds more affected by a mysterious gas cloud that drifted in off the sea in east sussex. the third round of brexit talks take place in brussels this afternoon, with british negotiators urging the eu to show flexibility and imagination. police and troops have been deployed in the north indian city of rohtak, where a controversial guru is due to be sentenced shortly for raping two women. now on bbc news, the bbc weather team on why city weather is so different

from coast or countryside. this time on weather world, we're at the highest point of the uk's biggest city, uncovering the secrets of urban weather. and finding out why heatwaves hit cities and those of us who live in them the hardest. we take to the rooftops of london to see just how man—made environments can change the weather. what are you hoping to achieve in the future? when we do weather forecasts, we will give more detailed forecasts, so there will be differences between different parts of the city. also on weather world: out of nowhere. the driver's—eye view of mudslides and storms, as we take a meteorological tour of the world. scorching summer in southern europe and the deadly consequences of wildfires that rage out of control. watch the birth of a flood as it surges down a dry riverbed,

to the floods that sweep away everything in their path and the disaster they cause. plus, cold comfort. the blanket response to melting glaciers in the austrian alps. scientists have realised there has been an unprecedented glacial melt, so the questions now are how serious is that melt and what can they do to stop it? welcome to weather world and a view once seen you'll never forget. the view from the shard, a skyscraper which stands above everything else in london. from up here you can see the haze that stretches over this urban landscape and tells you that the air is different here compared with in the countryside. and it is the unique properties of urban air which produces weather and climate differences which impact everyone who lives and works in a city. it's called the urban

heat island effect. an urban heat island is a built up or man—made area that is significantly warmer than the surrounding countryside. it's often most noticeable overnight when the temperature difference can be as much as 12 celsius between the inner city and the rural surroundings. there are several causes of the urban heat island effect. firstly, dark surfaces and the type of materials used in cities, such as concrete and tarmac, tend to absorb more solar radiation during the day and heat up quicker than the countryside. this heat is then released into the city air, creating a warming effect. with higher levels of particles and pollutants in the air in cities, that air is more capable of holding onto the heat, whereas in the countryside where the air is often clearer, more of that heat can pass through the atmosphere. there's also a lack of evaporation in cities due to less vegetation and fewer bodies water. in more rural areas, this evaporation from trees and water removes heat from the surrounding area. as well as the materials used

in cities, the other major contributing factor is the topography of the structure of urban areas. imagine, for instance, wind flowing in a relatively straight line across open countryside. when that wind blows across an urban area, the buildings create more friction to the flow, making it slower and more turbulent. this in turn reduces the winds capacity to disperse heat. so with more than half the world's population living in urban areas, this heat island effect has a huge impact on our weather and daily lives. we're swapping one high—rise for another, as we cross the city from south to north, joining a team of scientists investigating urban weather. what they're discovering could one day narrow down weather forecasts from whole to parts of the city and perhaps even individual streets. behind me you can see the shard on the london skyline, and as part of the research project here there are various pieces of meteorological equipment taking readings of different elements

of the weather. one of those pieces of equipment is inside this silver box here and that's a thermal imaging infrared camera. this camera is looking down at the city and is taking measurements of temperature coming off different materials, buildings, for instance, roads and vegetation too. so to tell us more about this camera and what is it's measuring we're going to meet phd student will morrison. hi, will. hi, sarah. talk me through this camera. what exactly is it looking at and what is it showing us? this is a long—wave infrared camera, sensitive to long—wave infrared radiation, which can be used to determine surface temperatures. so if i was to point the camera at different surfaces, like my hand, surfaces of different temperature would appear a different colour? yes, this is a thermal graph of the temperatures which you can see through the camera. your hand is appearing cooler than the surroundings. the different colours represent different temperatures, in this case. great. let's have a look at how this works in action, looking down at the city.

absolutely. so, will, you've got several of these infrared cameras positioned at different places around the building. this one here is looking down at some buildings, some roads and vegetation down below us. talk us through what it looks like and what we're seeing on the infrared image. this is a time lapse of the imagery. you can see the same principle as with your hand, different colours representing different temperatures. we can see there's a variety of colours, meaning the surface and temperatures are highly variable. why are we interested in these measurements? typically we use satellite based measurements of surface temperatures, which are looking straight down at the surface. that means they have a preferential view of the roof and ground surfaces, as opposed to all surfaces. i'm doing a ground proofing exercise here, with lots of measurements from different angles, to build up a complete picture. so these surfaces are really important for evaluation

and input for forecasts. and we'll have more from the rooftop later. when the going gets hot, you do what you can to stay cool. it's been a summer of extreme heat in southern europe, with temperatures soaring well into the 40s celsius from spain, across to the balkans. in italy, the heat exacerbated drought. this is the bed of the river po. so the pope ordered the famous fountains of the vatican to be turned off, to show solidarity with the people of italy and rome, where temperatures hit 43 celsius. hot, dry and now on fire. wildfires led to thousands being evacuated from camp sites here in france, injuly, spending the night on beaches near saint—tropez, as the smoke billowed above them. portugal in june, and a catastrophic forest fire kills more than 60 people. the country's worst disaster for more than 25 years. the majority of people were killed on this road,

rapidly engulfed by fire as families already fleeing from their homes were trying to drive to safety. more fire, but a different continent. this is south africa, near cape town, injune, as severe drought combines with strong winds to spread wildfire sparked by lightning. they followed a major storm that inundated the coastline here, with high seas and big waves. the south african weather service said it was the worst winter storm here in 30 years. big storms have hit europe too. this is moscow, in may. a severe thunderstorm, the worst in a century, kills 16 people, toppling trees, with winds of up to 70 mph. and astonishing scenes from poland, in august, as storms bring down tens of thousands of trees, killing six people. the country's chief forecaster called it the worst disaster in the history of polish and perhaps european forestry. storms brought devastating

downpours too. turkey and istanbul, injuly. roads turn to rivers. rail tracks turned to rivers. there have been a number of flooding storms in the city this summer. in the uk, storms followed a hot start to the summer. this is cornwall, injuly. and in coverack, the torrential rain and hail lasted over an hour, causing a flash flood to sweep through the village, taking everything it could carry towards the sea. this woman found her elderly mother's walking frame among the piles of debris and next to it even her kitchen sink. it's happened. we can't put it back. you just have to get on and carry on and do what we can. we'll get back to normal. we're cornish! earlier in the summer, a heatwave provoked an unusual protest at a devon school. boys told they couldn't wear shorts in the heat, because it wasn't official school uniform, wore skirts instead. everyone was like, oh, if everyone else does it,

they can't stop anyone else doing it, so they might bring shorts back for the summer. well, girls are allowed to wear skirts all year round. they get cold legs and we have to sit there sweating! the school says as hot weather becomes more common, it may consider a change. protest is real! we are back at our urban experiment on a rooftop in london. earlier, sarah and will were using thermal imaging to look at how different surfaces, grass, concrete, humans, heat and release the heat at different levels. that's enough of that. but that's really important because those different surfaces are also heating the air above them at different levels, different rising of that air. that goes on to affect the air around us in the city, but also the weather too. ben crawford is monitoring just how much the air is moving around us with this piece of kit here. tell us about it, ben. that's right. this is a 3d sonic anemometer. so it measures wind speeds in three dimensions. with this piece of equipment we can

measure the cumulative effect of all the different surfaces and their heating of the air. so, importantly, i'm feeling the air blowing right at me sideways, now, but when you are talking about different surfaces heating the air above, it's rising from the ground upwards, which you're also measuring with this. and you would expect that air to be rising differently, depending on where it's come from — grass, concrete, tarmac? yeah, exactly right. if you imagine a natural environment, like a field or forest, and you replace that with a city, with glass and concrete and brick, you will change the thermal properties of that surface and change how the air flows and moves. this is measuring what's going on just here, but you've also got another piece of kit here, which is measuring over a bigger distance, isn't it? that's right. this is called a scintillometer. so it measures disturbances from the air, from the heat rising, similar to shimmers coming off a hot roof or a hot piece of concrete. so this is pointed across the city towards suffolk towers, about four kilometres away.

so this really is the invisible world of what's going on in the air right above this cityscape and above us? that's right. and with the data from this instrument we can make the invisible visible. so here we have a series of days in the summertime here in london and we can see during the midday, the hottest part of the day, we have the greatest heat emissions and we can see this rise in the graph. 0vernight, when the surface has cooled down, we see less heat emissions coming off the surface. but what does it matter? how does knowing about all of this turbulent air possibly improve a weather forecast for a city? that's a good question. heat emissions and turbulence affects a lot of things. it affects air temperature, wind speed, it affects the dispersal of air pollutants and can even impact things like clouds. so we can narrow down the forecast to a much smaller part of the city? that's right. we can give a specific forecast for a city, versus a rural area, and maybe in the future even

different neighbourhoods within a city. thanks for revealing the hidden world of what's going on in the air around us. you're very welcome. oh my god! clear! turbulence and updraughts when airborne are what hot—air balloons try to avoid. but getting airborne is the problem here. we're trying to get air up, so we can get up. two balloons collide in the usa injune. swirling, shifting winds on the ground blow them off course. luckily, what could have ended in tragedy only left one man with minor injuries. lightning sparks across the south wales sky in may. the earth's surface is struck about 100 times every second and whenever lightning strikes you can be sure bbc weather watchers will try to succeed where many of us fail to get a good photo of it. these were all taken when storms swept through the uk injuly. become a bbc weather watcher by signing up online. and coming up, how a blanket

could help produce a phenomenon known as glacial melt. so far on weather world, we've been getting very high—tech at this urban weather experiment on this windy rooftop in london. but along with the high—tech, i'm glad ifound something that's a little bit more familiar, at least to me, which is a weather station. we've seen a lot of these on our travels on weather world. remember, in northumberland, we saw a fully working met office weather station there. inside here we've got a thermometer and it's measuring humidity with this gauge, all inside a very clever box which protects it from the direct sunshine and excessive wind... of course that weather station had a stevenson screen behind which you had a thermometer. this, although not the same as a stevenson screen, acts like that, protecting that thermometer, so it can measure the temperature of the air, rather than the sun, getting to that thermometer. and we've also got, look at this, a cup anemometer. look at it moving in the wind today.

and we've been to the birthplace of these anemometers on our travels in weather world, to armagh, in northern ireland. michael, i've got an amateur weather station in my back garden and it has this on it. and to think it all started here, in armagh. that's right. a simple design, four cups that spin in the wind, and you can measure the wind speed and that's how we know wind speeds around the world today... well, this anemometer is getting a good workout today, but it's really good to know that wherever we go on weather world we can find a weather station. but we will get a little bit more high—tech again later in the programme when we come back here. in—car dash—cam technology can now give us a driver's eye view of what it is like to negotiate a mud—covered, flooded road. but things are about to get much worse. china injuly, and a dramatic mudslide, after days of heavy rain, leaves drivers buried and many needing rescue. here, only injuries, but in bangladesh injune,

a desperate search for survivors as heavy rain triggers a landslide that kills more than 100 people. from sri lanka north to nepal, the monsoon rains so vital for crops bring floods that affect millions. in nepal, the floods worsen in august, and elephants are used to rescue people trapped in rising water and take them to safety. injune, torrential rain in taiwan. more than 600 millimetres in less than twelve hours. similar scenes in japan in july. described as unprecedented, the rain forces more than half a million people out of their homes. when a flash flood rushes a major city, disaster strikes. freetown, the capital of sierra leone, in august, and a massive downpour causes muddy water to certain industries. then a mountainside collapses, burying whole communities and families, as they slept.

hundreds are under this mud, and the death toll may never be known. it is the rainy season here, but this year, it has come with unusual and deadly ferocity. and just how quickly can rain transform a dried out, dusty river bed, into a raging torrent? this quickly. the usa, and arizona in august, as a flood of water, mud, and debris, suddenly surges out of nowhere, catching campers by surprise, as they scramble to rescue their belongings. a happier surprise for some in the southern hemisphere winter, as a rare snowfall his the chilean capital, santiago, in july. the snow caused widespread power outages, and treacherous driving conditions — not that these motorists seem to care. but unusual cold snaps look like local anomalies against a tide of record warmth. alaska.

parts of this us state had its warmestjuly on record. in may, the artic council meeting here signed an agreement accepting the need to tackle climate change. but less than a month later, this. in order to fulfil my solemn duty to protect america and its citizens, the united states will withdraw from the paris climate accord. president trump's announcement brought widespread international condemnation. the un world meteorological association said that in the worst case, the us pull—out could add 0.3 degrees celsius to world temperatures by the end of the century. away from the global political battles, there

are smaller scale fights on the way to try and stop local environments from changing, perhaps irreversibly, as sara thornton has been finding out in austria. i'm at the top of the stubai glacier in the austrian alps, at about 3,000m high. it's an area that's very popular for skiing. and actually, there are about 80 separate glaciers in this area. but there's a problem, because in the last few years, scientists have realised there has been unprecedented glacial melt. the questions now are, how serious is that melt, and what can they do to stop it? dr andrea fischer is a world—renowned glaciologist, who's made it her life's work to halt the decline of this glacier. she has hit upon a surprising answer, a blanket. covering the glacier and preventing ice melt. on a very small, very local scale, we could prevent some very tiny glacial areas by covering them with sheer textiles in summer. but only about 1% of glacier area can be preserved with this method, and of course, it's very cost

intensive and needs much labour. to save 1% of the glacier seems almost futile, but with the local economy relying on skiing and tourism here, officials say it's worth it. there are 5000 alpine glaciers in the world. and some scientists predict that at the current rate of melting, in 20 years, half will be gone, and those that are left will be much smaller. but it is far from clear if this expensive local solution can help on a global scale. here on the vast greenland ice sheet, the problem is super—sized. there are fears that the melting is happening faster than expected, in part due to algae growing on the surface of the ice. darker than the ice, it absorbs more of the sun's warmth. the more the ice melts, the more sea levels rise. nobody is saying that is going

to melt in the next decade, the next 100, or even 1000 years. but it does not need to be completely melted for people to be in danger. only a small portion is required to raise sea levels, and to threaten millions of people coastal communities around the world. and in the expansion of renewable energy, this is a landmark development: wind turbines floating in the sea of norway. they will form the world's first floating wind farm. so, you've looked down towards the ground, and we've seen equipment measuring the weather at this level. but now we look up into the skies. to do that, i am joined by natalie. hi, natalie. talk us through this piece of equipment, here. ok, so this is the cellometer, a laser that takes a vertical snapshot of the atmosphere. this is the equipment that holds the laser.

you can't see the laser. it measures outside the visible spectrum. so this looks 7000 kilometres up into the sky. what is it measuring? it is measuring reflection from particles in the atmosphere. this could be cloud droplets or air pollution. with that, you can see at what height the clouds are. so you can get a picture of the height of the clouds and have a picture of how polluted the air is at any time. yes. ok, so we've had a look at this cellometer. we will go around and talk to sue, who will give us an indication of what the output from the cellometer looks like and how we can use that data. now, sue is an urban climatologist with the university of reading, and she's heading up the research here. so, sue, hi, we havejust been talking to natalie about the cellometer, and how that measures cloud height and particles in the atmosphere. so how is that information useful to you? it's helping us with our weather forecasts. we can see where clouds form.

what we are looking at now is the green is the rural area, and the grey is the city. you can see the clouds are forming, what happens to them as they form, and over cities, that is different. we can compare the difference in the real city with what we can see in forecasts like this. so with all the research going on here, then, how does that tie together, and what are you hoping to achieve in the future? what we are trying to do, and as we we think about forecasting into the future, what we are expecting is that models will allow us to look at things in much more detail, so we can look at, for example, the differences between the northern part of the city and the southern part of the city. hopefully this will make it better for citizens within the city and living in different neighbourhoods. wonderful. so we're looking at more accurate urban forecasting the future. thank you forjoining us, sue, and for all your team, too. sometimes you need to look over your shoulder to see what the weather's doing. this photo of a man unwilling

to abandon mowing his lawn in canada injune took social media by storm. apparently, the tornado was further away than it looked. we often show pictures of the aurora borealis, or northern lights, but these are the southern hemisphere equivalent — the aurora australis, putting on a spectacular show in the skies above australia and new zealand in may. and finally, the weather can make us all a little hot and bothered at times. and apparently the same goes for gorillas. zola, creating a splash at dallas zoo. and that's it for this time on weather world. we will be back later in the year. until then, keep checking the forecast. so talk us through...

we neverfilm when it's hot! we can measure disturbances from the airflow... could be the hottest late august bank holiday we have recorded, temperatures potentially up to 29, 30 in the south east, it will turn cooler as we go through the next few days but with high—pressure returning by the weekend things settling down and becoming dry and settled again. for this morning and much of england and wales looking at

lots of sunshine, scotland and northern ireland with rain coming south and east, this afternoon fine and dry and the sunny weather continues, into the midlands temperatures getting to the mid to high 20s. a bit cooler further north and west and that cloud spilling from the north—west but still temperatures of about 23 degrees, the rain across northern ireland into the south west of scotland by the stage in the afternoon, the north and north—east of scotland seeing things improving and temperatures up to about 21 degrees but it will be a hot day across the central and eastern parts of england in particular, the further north and west you are it will be that bit more fresh. through tonight this area of cloud and rain moves its way south and east, it will break as it does so, introducing cooler conditions, chilly night, across england and wales still thoroughly warm with tempter is no lower than 15-17d. this

warm with tempter is no lower than 15—17d. this area of cloud and rain as it moves south and east will break up as it does so, there will not be much rain but to the south east of england it will remain dry, temperatures up to 26 degrees but much fresher conditions coming into northern and western areas. going into wednesday, two areas of low pressure, more cloud and rain, for scotla nd pressure, more cloud and rain, for scotland and northern ireland it should be largely dry with sunshine, witty weight at times for england and wales, the temperatures down to 18 celsius, much cooler and fresher across—the—board. thursday 18 celsius, much cooler and fresher across—the—boa rd. thursday into friday things improve, showers around at times but temperatures 16-20dc, around at times but temperatures 16—20dc, going into the weekend you look thoroughly settled. that's it from me, goodbye. this is bbc news. i'm joanna gosling. the headlines at ten.

thousands more people in houston are told to leave their homes as floodwaters continued to rise in the trail of tropical storm fitow the. 0ne care home had to be evacuated after residents found themselves stuck in waist—deep water. more than 130 people have been treated in hospital and hundreds more affected by a mysterious gas cloud that drifted in off the sea in east sussex. formal brexit talks resume in brussels today — with british negotiators urging the eu to show flexibility and imagination. also in the next hour: pretty vacant. more than a year on from the final store closing, over half the shops are still sitting empty. and in half an hour, newsbeat asks if it's time for change to attitudes to the legalisation of cannabis.