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Researchers in Leipzig show how green roofs and rainwater management can reduce urban heat. Also: climate change, biodiversity loss and the growing threat posed by invasive species.
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00:05in Europe the summer of 2026 was one of the hottest since record-taking began when temperatures
00:11climbed that high cities turn into ovens movement is exhausting and everyone seems
00:17on edge we need to do more to adapt particularly in urban settings more green spaces could be part
00:23of the solution this and more on dw's science show welcome to tomorrow today
00:36can we redesign cities before urban heat becomes even deadlier this researcher is on a mission to
00:43do just that fabian brandenburg and his team in leipzig use green building and urban design along
00:50with stormwater technology to help defend germany cities against the blistering heat caused by
00:56climate change cities are typically hotter than their surrounding environment due to the high
01:02density of materials like metal concrete and brick that absorb heat a lack of vegetation also plays a
01:09role during extreme heat air temperatures in inner city centers can be higher by up to 10 degrees
01:16celsius than the adjacent rural and suburban areas a danger for the people who live in urban settings
01:22in particular the elderly who are especially vulnerable to hot weather fabian and his colleagues
01:30investigate the cooling impact of patches of plants and swamp vegetation on roofs where the conditions
01:36mimic marshland compared to roofs covered in gravel what we can see is that the surface temperature of the
01:45roofs is several degrees lower in summer when you compare it to the gravel roof the green and swamp
01:54roofs act as an extra layer of insulation just soil the substrate or in case of the swamp green roof
02:03water
02:03acts as an insulation barrier just like you would normally insulate your building and in addition you
02:12have evapotranspiration effect so kind of the building is sweating just like we would and evapotranspiration then
02:21cools the building water for evapotranspiration comes mainly from rain which fills gaps in the soil when
02:29it falls roots absorb the water and draw it upwards through the plant's body it's then released through
02:35tiny pores on its leaves as water vapor this vapor has a cooling effect on the surrounding air in urban
02:42areas it can amount to as much as four degrees celsius
02:49evapotranspiration is one way plants cool their surrounding environment another is shade from their
02:57leaves these are germany's first tree trenches they collect storm water to prevent flooding and that
03:04water is handy in times of drought what we saw here over the past years of drought is that a
03:11lot of trees
03:12actually died and thereby they lose their infrastructure function so to say so they don't provide any shade and
03:19they don't evapotranspiration any water and by um specifically um infiltrating rainwater at the tree
03:28trenches or at the parks we can keep the tree alive and thereby it keeps its benefits like shade and
03:36evapotranspiration the tree trenches can give the plant's roots more space underground combined with
03:43collected storm water this can lead to bigger canopies and better shading which means cooler
03:48streets green infrastructure can be as simple as a dip in the grass cobbles which let vegetation
03:55through or funnels channeling storm water towards surrounding greenery new buildings could pump gray
04:03water wastewater not contaminated with feces to the green roof an experiment here shows plants fed with
04:10wastewater thrive even more than those fed with tap water the system helps keep plants alive when water
04:17is scarce and could help them provide more shade in the city the scientists also work with rain water
04:24collected by their green roofs they found that piping the rain water down the walls has a cooling effect
04:32the research may prove beneficial further afield than germany especially in regions where water is scarce
04:39blue green infrastructures are especially important because they not only retain water on top of the roof but
04:49they also infiltrate it and can recharge the aquifers or the the groundwater clean water scarcity is an issue
04:58for indonesia's cities this is professor felix koitzig an expert in the field in indonesia green roofs make a
05:08lot of sense um and the reason is like in that compared to germany they are like in germany there
05:14are a few weeks where it's really really hot in indonesia it's most of the year quite hot and additional
05:20cooling um actually has like the benefit it cools down like for all times of the year so that's like
05:26a
05:26huge um additional advantage that the benefits actually spread out of all over the year
05:32having a standing body of water like a swamp on a roof in indonesia could be problematic for controlling
05:39mosquitoes though but green roofs because they retain water could help protect a city like jakarta
05:46from flooding during storms and therefore reduce sudden runoff however indonesia's humid climate could
05:53raise issues in indonesia like um plants are different like of course there's importance to
06:00to use native plants it's more humid um plants are growing faster and that can lead to structural
06:07issues like um you need like earth and the plants itself the biomass it's weighing so like the buildings
06:14need to be stable enough to carry the weight off with the biomass and that's an important consideration
06:21a common criticism of green roofs is that the cost of installing them is just too high
06:28but fabian says blue green infrastructures will actually save leipzig 700 million euros over the next decade
06:35and by lowering urban temperatures installing greenery to reduce extreme heat will also save lives
06:45do you have a science question then send it to us as a video text or voice message
06:51if we answer it in the show we'll send you a little gift as a thank you so just ask
07:00how is climate change affecting biodiversity plants animals fungi we share our planet with millions of other
07:12species all interacting in different environments this is what we think of as biodiversity and it's
07:19threatened by climate change especially by rising temperatures habitats often change faster than the
07:27species that live in them can adapt like the polar bear polar regions have grown warmer in the last few
07:34decades causing vast stretches of sea ice to melt and that's having an impact on polar bears which depend
07:41on the ice to hunt seals elsewhere water is growing scarce forests are suffering as a result trees don't react
07:50quickly to environmental change they take a long time to reproduce and adapt to new circumstances
07:57when weakened by drought they absorb less co2 and produce less oxygen that leaves them more vulnerable to pests
08:05and wildfires climate change is also altering the timing of some natural events many plants now flower earlier in the
08:15year
08:16than they did just a few decades ago this is causing major problems for bees they arrive too late and
08:23miss out on
08:24important food sources and plants miss out on their pollinating services warmer temperatures are also causing some
08:32caterpillars to emerge earlier that affects birds like the great tit which raises its young in tandem with the
08:39insects life cycle if the caterpillar prey has already pupated it can seriously affect a crucial feeding period
08:46for the young birds the effects of climate change on biodiversity are complex and often less visible than melting
08:55glaciers or dried up rivers because in an ecosystem everything is interconnected
09:02and when one species suffers the consequences can have an impact on many others
09:11meadows and forest ecosystems are home to a remarkable number of species
09:16but that diversity is now under threat using a wide range of methods researchers
09:21in germany are looking into what causes biodiversity loss
09:26a meadow near jena in central germany divided into rectangular plots
09:33we set up different plots where randomly selected plant species grow in varying numbers
09:39altogether we have 80 plots containing either just one species or two four eight 16 or 60 species
09:48and we've replicated the whole setup several times so we have multiple monocultures of different species
09:55and can investigate what happens when species are missing
10:02each plot differs in both the number of plant species and the species composition
10:07the goal is to find out how plant diversity affects both wildlife and the soil researchers use a range of
10:15tools to measure that
10:20the soil
10:21here they're testing how much sunlight makes its way through the vegetation to the soil
10:29something else the researchers are interested in is soil moisture
10:36they even use a vacuum cleaner
10:55anna abeling vacuums a cubic meter of air and vegetation to find out exactly which insect species live in the
11:03different sections of the meadow and how many of them there are
11:09and she checks whether there's a link between the number of plant species
11:13and the number of insect species on the various test plots
11:22another experiment aims to find out with the help of a decoy which predators are active here
11:29for this we use these green caterpillars made of modeling clay
11:35we place them in the plots and collect them again after 24 hours
11:41the caterpillars simulate real prey that might attract all kinds of predatory insects
11:46you can actually tell from the shape of the bite marks which groups have attacked them
11:50this one for example has mandible marks that we know are made by certain predator beetles
12:01the second green decoy bears the marks of a bird's beak
12:05most likely from a small songbird that thought it had found a tasty snack to bring back to its chicks
12:21it's just ordinary clay it's a surprisingly simple scientific method we make them using a
12:28meat grinder fitted with a pasta attachment when the clay is pushed through the grinder
12:34you get slender green caterpillars we then cut them to a standardized length and use them as imitation prey
12:45over many years we've consistently seen the same pattern greater plant diversity leads to higher
12:53predation rates from that we can conclude that natural pest control which is effectively what
12:58predation is increases when we have many different species in an ecosystem the more varied and numerous
13:07plants there are per square meter the more insect predators like lacewing larvae that feed on aphids
13:15or ladybugs high plant diversity therefore promotes natural pest control
13:21the plots with the greatest plant diversity also perform best when it comes to soil moisture and biomass production
13:32plant diversity had a huge positive effect on the vast majority of the processes we studied
13:39and the more plant species there are the more butterflies
13:44the more beetles
13:49and the more spiders making the meadow an especially productive ecosystem
13:56but even under ideal conditions the insects and other small creatures reveal a worrying trend
14:04we analyzed data from 2010 to 2020 and in that period alone some groups declined by as much as nine
14:12percent per year when we lose species we also lose the functions they perform that's crucial not only for
14:19people who enjoy walking through a meadow but for all of us if we no longer have pollinators then one
14:25day
14:25apple trees will no longer be pollinated yields will fall and so on a greenhouse near bad lauchstedt
14:36here marie lara bouffaut and her team study young oak trees at the german center for integrative
14:43biodiversity research somewhat older trees grow on the meadow outside the young saplings raised in
14:51these high-tech containers are monitored closely cameras and sensors collect data on their growth and
14:59metabolism around the clock the biggest difference between containers is how much water the trees are
15:06given we look at the response of the trees and all they react to several years of drought and this
15:15is
15:16something we experienced in the last years in germany so we want to mimic the dry seasons so we control
15:24the watering so the amount of water which is applied to the plants we also installed a net on the
15:31top
15:31of the trees to avoid that insects are coming inside humans work side by side with the machines to collect
15:40data so we have different sensors on the side so we have sensors that measure soil temperature and soil
15:47humidity we also measure different parameters on the trees themselves so all they grow or much they grow
15:54how many leaves are produced or biomass which is produced we also measure some photosynthesis and
16:01gas exchange so all the plants transpire and respire so what are the fluxes of nutrients in the trees
16:12the oak trees being monitored here are all exactly the same age even so there are major differences in
16:20growth too little water severely limits development
16:28and there's another factor that can have a major impact on the health of the trees
16:35and we also saw some from some experiments in the fields in the past that
16:41drought has really an impact also on the soil community so we have a lot of partners in the soil
16:47we have bacteria fungi nematodes a lot of arthropods that are living in the soil naturally and some
16:54are really helping the plants to cope with stress events like drought in return the plants release
17:02nutrients through their roots that feed the tiny soil dwellers in the lab the team studies how they
17:08are affected by the experiments adding water to soil samples to filter out the organisms they contain
17:14the researchers are particularly interested in tiny worms called nematodes we want to see what is the
17:23interaction between the microbiome and the nematode and how that affects the tree itself
17:33do samples from containers where saplings are particularly vigorous contain different nematodes
17:39in the containers where the young trees are scrawny and unhealthy a microscope can help provide clarity
17:45i usually look at first of all the head the mouth rather of the nematode and then here i see
17:53that there
17:53is a stylet it's kind of like a sword so it's characteristic of a plant feeder and they use this
18:01stylet to
18:03pierce into the root the plant root
18:10like much larger beetle larvae nematodes can cause considerable damage to roots
18:18fortunately plants have allies underground as well
18:22in general the soil biota is a good helper of of the plant and um the other free living nematodes
18:34they
18:34are also have a indirect positive effect on the plant and for example predator nematodes they can help
18:46regulate these plant parasites a rich diversity of life in the soil therefore plays a key role
18:54in keeping forests healthy
18:59an ongoing study at the german center for integrative biodiversity research in leipzig
19:05is focused on creepy crawly creatures roe van klink is trying to find out which species of beetle
19:11live in this unused field to do that he sets traps when the insects and other organisms fall into these
19:21jars buried in the soil they can't get back out
19:31what we have today for example is a ground beetle from the genus amara also a snail a small spider
19:39another
19:40ground beetle a wood louse not that much normally there would be a liquid inside and the animals
19:47would die then we take them back to the lab and identify them down to the species level
19:53we count all the individuals from each species and analyze how things have changed over the past three
20:00or four years identifying beetle species can be straightforward the difference between the
20:08asian ladybug on the left and the european one on the right is obvious even to non-experts
20:15with ladybugs it's often quite obvious but these ground beetles for example are four different
20:20species yet they all look exactly the same like ours many of them may look alike but beetles play very
20:29different roles in the ecosystem some are predators while others feed on carrion some are widespread and
20:36common others are rare and found only in specific regions that's why it's important to be able to
20:42distinguish reliably between species in identifying them the smallest details make all the difference
20:52i'm looking along the sides of the pronodum according to this identification guide they're an
20:59important feature for distinguishing between these two species of the genus nebria which is a group of
21:06ground beetles both species are common but one has a broad margin and the other a narrow one i think
21:15this
21:15one is nibria brevicollis another beetle correctly identified and roe van klink meticulously identifies
21:26all the other organisms from the traps as well species are important because they're the foundation of
21:35everything we do we need to know how many individuals belong to each species
21:42that's essential for our work as researchers because it allows us to assess the state of biodiversity
21:49but it's also important for conservation because conservation measures are often based on individual
21:55species some species are protected others are not so we have to know exactly which species we have
22:06one finding from this basic research is that insect populations are declining dramatically
22:13some species have already disappeared completely so what's causing it
22:22it turns out that identifying causes is difficult we have a list of perhaps 12
22:28to 20 different factors that could be contributing but there are very few studies that can really say
22:35this is what happened to these insect groups at this particular location
22:42one important factor is certainly land use fields like these may reliably produce grain for human
22:49consumption but insects are unable to thrive there
22:55it may well be that animals disappear out there and nobody notices but that doesn't make it okay
23:01for me it's an important ethical question it's simply not acceptable that we humans cause other
23:08species to go completely extinct
23:14and if things have reached the point where our actions are wiping out other species
23:20whether animal or plant then we have a moral responsibility to prevent it if we can
23:32climate change is driving some insects to extinction while helping others spread invasive species like the giant
23:38glandular ant the asian hornet or the tiger mosquito an aggressive daytime biter then there's the japanese beetle
23:52the grapes in the swiss wine growing region of ticino are especially sweet this year
23:57the pests seem to agree once again the japanese beetle has revealed its destructive potential
24:04matthia vossin has experienced the damage firsthand the japanese beetles ate practically everything
24:13the japanese beetles ate practically everything there were up to 20 of them on a single leaf
24:20i guess at least 200 beetles per vine
24:26in 2025 10 million beetles were collected more than twice as many as the year before
24:32the numbers expected to be even higher in 2026 originally the insects came from regions south
24:39of the alps but they made their way north hitching rides in cars trucks and trains
24:45there are very few effective control measures you have to combine them otherwise you have no chance of
24:52controlling these pests another challenge is that the beetle can dine on a very long list of host plants
25:00plants on football fields on roses in gardens on fruit trees it can feed on more than 400 plant species
25:09swiss fruit farmers are seriously worried we shouldn't take this lightly and think it'll sort itself out
25:17things can escalate very quickly ideally we should find the beetle's natural counterbalance species and
25:24introduce it there are many possible approaches but so far no solutions
25:30and by the time indigenous birds and spiders discover the japanese beetle as a possible food source
25:38it could be too little too late
25:45and that wraps things up this time on dw's science show
25:52thanks for joining us and hope to see you again soon on tomorrow today bye for now