 Welcome, ladies and gentlemen, to this first masterclass in the online masterclass series, Urbanizing Deltas of the World. My name is Jaap Evers and I'm a senior lecturer in Water and Environmental Policy at IHE Delft, and I will be facilitating today's masterclass series. The speakers in our masterclass series all participated as PhD or postdoc research fellows in one of the research projects supported by the Urbanizing Deltas of the World Program of the Netherlands Research Organization, NWO. And via this masterclass series, they will be presenting their work and insights to you. And you will have the opportunity to ask questions on the topic today. In every masterclass, we will have two main speakers. And let me take the opportunity to explain the setup of this masterclass. So there we are, that looks better. So first today, we start with the presentation of Dr. Philip Mindenhout. And that takes about 30 minutes. And as we are broadcasting on YouTube, you have the availability to write down your questions and comments in the comment box below the video. Please share your comments as soon as possible and do not wait until the end of the second speaker as there is a little bit of a delay of a minute or two between our recordings and the broadcasting to this live channel. And while Philip will give his presentation, me and my colleagues, Leon Hermans and Shanor Hassan, will collect your questions and we will merge and put them forward to our speakers. After Philip's presentation, we continue with the second presentation of Zeper Aslami. And again, his presentation will take about 30 minutes. So then please write down your questions and comments in the comment box. And maybe in order to prevent some confusion, please mention in the comment box when you have specifically a question to either Philip or Zeper. When Zeper has finished this presentation, we continue with a question and answer session and Philip and Zeper will give answers to those questions. If we do not have sufficient time to collect and give answers to all of your questions, we will answer them later also in the comment box directly to you. When it's about 10.55 local time, we will close this master class and we are going to thank you for your participation. I hope this is all clear. So let me now introduce you to our first speaker. Our first speaker is Dr. Philip Minderhout. Dr. Philip Minderhout was a PhD researcher in the NWO UDW project Rise and Fall. And this project aimed to develop sustainable strategies for groundwater extraction and management and to understand and quantify land subsidence and saltwater inflow and rapidly urbanized Mekong Delta in Vietnam. Philip is currently an assistant professor at the Wageningen University in the Netherlands and a Marie Curie research fellow at the University of Badova in Italy. He is also connected as an advisor to Del Dages. He is specialized on subsidence and relative sea level rise of coastal deltaic areas, affecting the fields of geology, hydro-geology, geotechnical engineering and remote sensing. His research focuses on increasing the fundamental understanding of processes and drives of deltaic subsidence and developing the numerical capacities to provide better spatial temporal assessments of current and projections of future deltaic subsidence. He is currently active in research on coastal areas around the world, still in the Mekong but also the Irawari, the Po, the Mississippi deltas and Manila Bay, north Java coastline and the Lagoon of Venice. Beside fundamental research, he focuses on impact-oriented research aiming to create awareness and collaborative research uptake and is actively engaging with policymakers and NGOs to develop strategies to cope with ongoing land subsidence and accelerated sea level rise. Let me now take the opportunity to thank you Philip for being with us here today and to share your knowledge and insights that you have developed over the past years with our audience. That being said, I give the floor to you. Thanks a lot Jaap for this very kind and extensive introduction and also thanks to you and the others of the organizing committee of these urbanizing deltas of the World Masterclass series. So I'm looking forward to this to give this masterclass the number one together with my colleague Sper. So hello to everyone and welcome to this masterclass getting grip on sinking, shrinking and saltier deltas. This masterclass is derived from the Rise and Fall project that we carried out starting from 2014 with a lot of different parties involved. You see some logos already here and I'll come back to that in a while. So it's been it's been worked by a large group of people. Some of them are mentioned on this slide and they also are part of the publications that followed from this. So here a short, let's say outline of this Rise and Fall program within the urbanizing deltas of the World Project program. It was a project that consisted of Dutch partners led by Utrecht University in the Netherlands together with Deltares, TNO, the Dutch Geological Survey and then several institutes and Canto University from Vietnam. So we really had Vietnam and the Netherlands as an entangled group of researchers and institutes. Here you see the prime suspects that worked on it. So we had two guys from Vietnam, Hung and Chi, then we had Saper working on the water dynamics and myself working on land subspecies. And it's quite nice to see our young pretty faces at the start of this project, which is already seven years ago now. So the outline of this masterclass is as followed. I will start talking about primarily land subspecies in deltas and then Saper will take over, talk more about dynamics of saltwater intrusion followed by this Q&A session afterwards. So I'd like to start with the following, to get everyone on the same page. So what is a delta and why do they matter? So a delta is a landform that forms when a river enters a body of water and it deposits sediments, mud, sand, clay to actually create new land, as you can see in this image on the right hand side. And these deltas are very valuable to us, they are densely populated, more than 500 million people worldwide live in these places and they have abundant resources, the land is very fertile, there's a lot of agricultural practices going on. And hence they're also very important for global food production and food security. So these deltas are places that play a very important role in actually humans living on planet Earth. Well these deltas have seen a lot of changes in the past centuries and decades. And here I'm going to show you how these changes, some of these changes. So here we see a natural cross-section of a delta before actually humans intervened in these landscapes. And then when we started to occupy these places, we started to change the land. So create land use changes, start agricultural practices. We started to settle in larger settlements and build cities. Then we started to use the natural resources, such as for example groundwater. Also in the upstream domain we started to develop a lot of infrastructural infrastructures, for example like dams for hydropower production. And these dams they block the flow of sediment and water to these deltas. And we take sand for example from the channels of the river. Well as you all know we are now living in an age with acceleration of climate change and that is causing a lot of stresses and changes in environments all around the world. So as a result we see an increase in the amount of floodings happening in these deltas. There's more and more saline intrusion in the surface channels. We see more coastal floodings occurring and events like gradual coastal erosion happening all over the world in these places. Also linked to the fact that we built these upstream dams blocking additional sediments to the coastlines. Also in the groundwater, saltwater is intruding and if we over extract for example groundwater there's more and more saltwater replacing the freshwater that was there before. And as you all know the sea levels rise because of global warming and depending on where you are on the globe this range is from 3 to 10 millimeters per year. But these deltas themselves are not stable they also experience land subsidence so they can sink and they can actually lose elevation and these rates can be quite high as you will see in this presentation. Well together these two effects the land going down and the sea going up is actually what we call relative sea level rise and this is what you experience when you are standing at the coastline and you just watch the water levels going up. So it is really the relative sea level rise that matters if you talk about these coastal places. So let's go to some of the major deltas on the world. So we see here some large systems the Amazon, Genghis Bama Putra for example the yellow right here is the Mekong and in colors you can see elevation and the warmer the color so the more red it means the lower the elevation of these deltas. So as you can see a lot of these deltas they are in this red zone meaning they are very low elevated above local sea level. So this makes them very sensitive to changes for example like climate change or changes by humans and this elevation is key because a low elevation to sea means that small changes can have already large impacts and actually the sinking of these deltas is something that is happening all around the world. Here are some studies from different deltas around the world that show measurements from space and the rate at which these deltas are currently sinking and you can see some of the rates they go up very high to several even decimeters per year. So this is one or two magnitudes larger than sea levels are rising and a recent study showed the following. So today the majority of the global relative sea level rise 50 to 70 percent experienced by humans is caused by land subsidence rather than the global warming induced sea level rise. So they looked at where are people actually living along the coastline and what is causing the relative sea level rise and they found that on a global scale land subsidence at the moment is more impactful than sea level rise. So what is causing land subsidence in these deltas? So here we have a cross section of a delta and a subsurface of sediments lying on top of bedrock. Well first of all land subsidence is a natural process. These sediments that are deposited by a river they are soft and they can compress over time and also when new sediment is added on top of them. So this is what we call loading. So the natural loading effect of other sediments biomass but also water during floods is causing pressure on the sediments in the subsurface and causes them to compact. Then there's also the component which is caused by let's say deeper rooted effects like tectonics and other earth cross dynamics. So land subsidence can be accelerated by human activities. As you can imagine the loading factor can be enhanced when we as humans build infrastructure on top of these deltas such as roads or buildings and they cause additional pressure on the soft sediments and cause compaction. But also when let's say when water is drained from these delta surfaces actually the water creates some sort of a buoyancy effect so it keeps it's actually lifting up the sediment. So when you drain the water there's actually a loading effect happening in the shallow subsurface and this is for example a main factor in the Netherlands which is causing a lot of compaction but also oxidation if you have organics in the shallow subsurface. And then there's the extraction of fluids from the subsurface. This can be water, this can be hydrocarbons, oil, gas and as you can imagine when you remove these types of resources from the subsurface the pressure is dropping and that causes land subsidence. So in general we see that land subsidence arranging from human induced processes tends to be much larger and faster than the natural induced processes. And also it can be very highly variable in time and space so depending on where you are in the delta other factors are more important in driving land subsidence. So let's go to the Mekong delta where we did our research. It is the third largest delta in the world and it's created by the river the Mekong that flows all the way from the Himalayas through Southeast Asia and then enters in the sea in the south of Vietnam. It is very densely populated 18 million people in the delta and almost 9 million people in Ho Chi Minh City which is in an adjacent delta very close to the Mekong delta and an experienced rapid development and it's dealing with all the challenges that we see in these modern urbanizing deltas. So when we started in 2014 what was already known in terms of land subsidence? Well recently just a couple of months before we started this study came out by Stanford University and they showed by satellite measurements the estimate of how much land subsidence was occurring in this delta and this was actually the first time that land subsidence was mapped or was being written about on this delta prior to that there was no reports on any land subsidence. So this study showed that something was going on and rates in the delta are sometimes in places going to 2-3 cm per year and then Ho Chi Minh City as an extremity with higher rates. And also when you are in the delta itself you can see the evidence of land subsidence. For example when you drive around and you look at the bridges you often see these kind of cracks or you see these kind of let's say newly constructed ramps in order to be able to drive onto these bridges because the bridge is founded at a deeper level and the road that leads to the bridge is unfounded so there's a differential compaction going on. So these are signs that there's shallow subsidence going on. And then when you find groundwater wells that can be going down to 200, 300, 400 meters and actually are in that way fixed at that depth they can show you a signal that subsidence may also happen at a much deeper level. So you can see these groundwater wells sticking out of the land for example here. This used to be the original surface when they created this one and now the present surface is much lower. So clearly there's subsidence happening in the Mekong Delta but the question is what is it actually causing it and also what does it hold for the future. So that's what we started to study in the end of 2014. And I'm going to take you through the journey that we made and I'm going to highlight three things that we actually discovered things on with our research. So the first was how much natural loading, natural compaction is actually happening in this delta. So what is the natural component? Then we looked into what is the impact of humans on land subsidence and we zoomed into the effect of the extraction of groundwater because we know that can be a very notorious factor for high rates of land subsidence. So let's go to the evolution of the Mekong Delta in the Holocene. It is very important to realize that landforms like deltas are actually very young landforms. They were only created between 7 and 6,000 years ago and this is because before that the sea level was much lower than it is today. So when we go back 7,000 years ago, the coastline would be somewhere about present day Cambodia. So when the Egyptians were building pyramids, the Mekong Delta as we see it on the map right here was actually not there yet. It was just an open sea. And since that time, this new delta was formed by a massive amount of sediments brought down by the Mekong Delta, creating this new and very flat landform. So there's a very rapid, what we call transgression, so growth of land that happened during the late Holocene in the last thousands of years. And all these deposits that are deposited in a shallow sea, which was about 20 meters deep, are very, let's say, new and young deposits. So it means they can actually compact quite a lot. So there are several, some sparse measurements available that actually measure really high rates of compaction in these top 20 meters. So some places you can go up to 5 centimeters, which is really a lot when you talk about natural compaction. And actually with modeling together with the University of Badawa, we were able to confirm that it's actually possible if you have such a young delta that progressed into the sea at such a high speed as the Mekong, you can actually create these unprecedented high compaction rates as a natural signal from this rapid delta evolution. And this is quite important to know because this factor, this natural compaction factor, is not something you can stop. So the only way is adaptation. So you have to bring in new sediments in order to compensate for the continuous elevation loss, which is also the natural mechanism that these deltas in a normal situation would sustain their coastlines. And we tried to make a first estimate of natural compaction. We see that here. And you can see that especially along the coastlines, there is this high signal of natural compaction occurring. So then we started to look at what can we see in terms of human impact and human control driving land subsets. So we compared this section of the Stanford measured rates from satellite with a series of land use maps that we created. And we analyzed correlations between these. So when we put them together, we found the following relation. So these are different land use classes up here. And these are the average rates of land subsets experienced by these different land use classes. And here are the drivers of land subsets. So the more classes you see, the stronger these drivers are related to these types of land use. And I'll walk you through it. So from the left to the right, we see an increase of human drivers with an increase of land subsets rates. But these two classes, marshland and wetland forest, are the natural classes. So they experience the lowest subsets rates. Then we have agricultural classes, which have a diverse range of the amount of land subsets they experience. And we see the highest rates occurring in urban environments. But we also expect most impact by human activities. But you see this outlier, let's say that the weird duck in the pond, it's the mangrove forest. But we can actually explain that. So this is a natural land use class, but they are situated along the coastline. And as you remember from the previous slides, this is the place where we have very high natural compaction. So that's actually what's explaining this relation here. So we see higher subsets rates with more human activities. OK. Then we focused, we decided to zoom in more on the extraction of groundwater. So let's have a look at what's happening in the Mekong Delta. It is a very fertile delta, and it creates a lot of rise, making Vietnam the second largest exporter of rise in the world. We also see vegetables, for example, these onion farms, more on the elevated reaches towards the coastline. There's fruit farming going on, especially in islands close to the river channels. In the upstream domain, in the freshwater domain, there's a lot of fish farms situated. And there's an increasing amount of shrimp farms in the coastal zone. Also, as a result of increased salinization, there's a conversion towards shrimp farming. And on top of that, the development in the delta also increased the amount of water used by industries and domestic use. So let's have a look at the groundwater use as we know it from the data in the delta. So at the start of the, in the 90s, there was not so much extraction going on. But then there was this really massive increase since this new millennium. And we see this really steep increase of extraction. Well, this water is coming from the subsurface in the Mekong delta. And it can be in places up to more than 500 meter thick. So this is 500 meter of unconsolidated sediments that contains water. And what we see from the measurements, if we look at the measurements that are situated in the different layers in the subsurface, we see a very interesting pattern. So we have measurements here from 1995. And this top one that you see here is actually the one that's connected with the surface bottom. So we see a seasonal trend of wet and dry season every year. But we don't really see a gradual decline over time. This is because the surface of the delta is still experiencing flooding. So there's a lot of recharge in this top aquifer that is openly connected. But then when we go to the aquifers that are located more in the subsurface and are actually closed off by clay layers from this top system, we see this gradual and steady consistent decrease in water pressure actually at all the depths. So this goes up to 400 meters in depth in this place. So we can see this disconnect between the surface system that is wet and that has a lot of water and the decrease of in pressure in this subsurface here. Well, and we know this can cause compaction in this thick pack of unconsolidated sediments. So how is this working? Well, it goes as follows. So the water is extracted from the sand layers that are in the subsurface. So these are sand and gravel. But in between the sand and gravel, there's also layers of clays and sills, small particles. And when we look into the skeleton of these sediments, it looks like this. So it's a sort of plates and that's quite a lot of space between them in which there's water. Well, what happens when you extract water and water has been pushed out of these, between these clays. So in a way, these clay particles, they behave the same as dirty plates in a sink. So this would be the natural sedimentation of dishes in a sink. There's a lot of pore space. There's a lot of room for in this case air but in also water in the subsurface. And then when you do the dishes, actually you remove a lot of the space and the same amount of dishes actually fit. They reorientate and they fit in a much smaller volume. And this is the same process that happens in the subsurface when water pressure is dropping and water is actually being pushed out of these clays and sills. So we see this realignment of these particles and the thinning of these layers. And that results in gradual lowering of the land surface. And I'd like to show you now a video abstract to give you some more insights on the work that we did on groundwater extraction. I hope Laura can help and put in on this movie. I heard something. I'm not seeing the movie appearing. I have to do it. I cannot press play. Okay, I cannot see the video. Sorry for that. Here we go. The Mekong Delta is one of the largest deltas in the world and it is inhabited by about 20 million people and it's producing food for almost 200 million people. The Mekong Delta is subsiding, but the amount of subsidence and the exact causes of subsidence are still unknown. What we see that there is a very high increase in groundwater use and we know that excessive groundwater use can cause land subsidence. The question is how much land subsidence is actually caused by the increase of groundwater use over the past 25 years. We build a large 3D hydrogeological model of the Mekong Delta in which we can simulate the groundwater use and extraction of the past 25 years and we use that simulation to calculate the amount of land subsidence caused by this groundwater extraction. On the left side we see the hydraulic head of one of the aquifers in the model and on the right side we see cumulative subsidence as a result of ongoing groundwater extraction. And then when we go through the model we see that there's a gradual increase in hydraulic head drop and then we see an increase of the cumulative subsidence. This is a nice example of what happens when you are extracting groundwater. So this used to be the old surface when the well was built here and now we see that the surface level is at least 30 centimeters lower. At the start of the muddling period the hydrogeological situation of the Delta was actually in a rather undisturbed state and if you talk about land subsidence caused by groundwater extraction there wasn't hardly any of that 20, 25 years ago. With the high subsidence rates that we see at present the Delta will get more vulnerable to flooding and there will be salinization in the surface water and in the groundwater. And this is putting pressure on the agricultural system in the Delta but also of course on the livelihood of the people living there. Okay, I'll stop it right here. We can go back to the PowerPoint. Great. So what you see, what you saw in this video was actually in the video abstract that was with the modeling that we created. So we created this 3D model as you've seen here from a lot of measurements in there and calibration. And when we run it we see this consistent drop in water pressure almost throughout this entire aquifer system. And here we see again this simulation from the movie. So on the left side this is water pressure going down and this is cumulative subsidence. So how much land subsidence this would cause. And what we saw and what we found was really this acceleration of land subsidence following this increasing trend of groundwater extraction. And the rates that we found were that actually extraction-induced subsidence is up to a magnitude higher than absolute sea level rise for this Delta. And interestingly, this was later confirmed also by more recent estimates of land subsidence by satellites. So here we have the Stanford study 2006, 2010 about two to three centimeters in places in the Delta. But this newer INSAR study that looks to much, let's say 10 years later, recent period, we see rates that go up five to six centimeters in quite some places in the Delta. So this acceleration that we first modeled we now also see in measurements. And we also see that the groundwater over-exploitation almost impacts the entire Delta. So it's really a widespread issue. So how can we use this model that we built actually to look into the future? Well, what we did is we created several different pathways of potential extractions for the future. So we have what we call non-mitigation scenarios in which groundwater extraction continues to grow into the future. And then mitigation scenarios in which different degrees of reduction of groundwater extraction. So this is what you could do if you would put policy on the extraction of groundwater. Well, we put that into the model and we could calculate the effects towards the end of the century. So with the higher extractions there's more and more depletion while if we reduce extractions there's actually an increase again in the water levels. When we look to land subsidence rates of course with higher depletions we see massive amounts of land subsidence in the future. But interestingly also when we go to the scenario in which we completely stop groundwater extraction there are still land subsidence happening. And this is because it's a delayed process of the dewatering of these clays. So it's an important realization to know that even if you stop today with extraction the process that is already let's say in place will still continue towards the future but at a much lower rate than if you continue to extract it. So then how do we know how much impact this has on the land? Well, for that you need to know the elevation of the delta. And I'm going to quickly skip these slides. These are let's say old elevation maps from satellite that were used. And they were used in a lot of reports but they gave quite a wrong impression of the delta as we can see here. So the average elevation from the widely used SCTM dam as it was used in these studies was about two and a half meters above sea level. But it looked really weird with all these striping. So we created our own elevation map using local points from Vietnamese data. And we actually arrived to an elevation that was much, that was even lower than one meter above sea level on average. Well, there's several two technical reasons for that. I will skip that in detail but what's most important to realize here is that the previous studies on the impact of sea level rise actually were using an elevation that was almost one and a half meters higher, almost two meters higher than the actual situation. So this is more than let's say a century of sea level rise. Well, as you can imagine, this caused a lot of impact in the media because people realized that this is quite a big thing. And also, for example, the MECOM River Committee, they released, let's say, they commented on this and they said, if the findings by Utrecht University are accurate, then the scientific community and government agencies need to update all their modeling works. And also the adaptation strategy and action plan needs to be carried out faster than we had planned. So it really shows that people were, let's say, motivated by this and that they realized that something had to be done. So if we combine this elevation together with these extraction pathways, we arrive to the following. So what happens if we would strongly reduce the amount of groundwater extraction? So the DM3 scenarios. So we only allow 25% of the current extractions. Then this would be the projection of the future elevation. And in blue is the area of the land that is currently at or below sea level at these moments in time. It doesn't mean flooded because it can be protected by dyke systems, but it means below sea level and that really increases the cost of living. We look to the M1 scenario, we see that quite a bit more of the delta is below sea level. And if we look to the moderate business as usual, gradual increase of groundwater extraction, by the end of the century, large parts of this delta will be situated below sea level. So there's a clear message here that the extraction of groundwater is not a free resource because you actually pay with it by elevation and elevation loss and also a certainization, as Seper will tell you about in the second part. I'll skip this one and maybe it comes back in the discussion. Quickly can reverse sedimentation compensate elevation loss only for a small part if you look to the massive rates. I'll go with that. So how to move forward in an econ delta? Well, at the moment, there's still not a measuring system of land subsidence. So the advice is to really install this system to make observations in situ of land subsidence. Mitigation is very important. So the reduction of groundwater extraction, that's a big thing. Do not extract more than is recharged, but there's also other options to do. So what are saving techniques or circular water management solutions? And for all the land subsidence that cannot be avoided, such as the natural compaction really reallowing natural sedimentation onto the delta plane is the only way to actually compensate the elevation loss. And it's important also to realize that trying to protect the entire delta with a dark system will be impossible. So it will create an irreversible situation, but also if you look purely to the size of this delta, it's not a feasible option. So some conclusions, I will quickly lay out and then we go to spare. So substance is caused by natural processes, but the majority by human activities, such as the extraction of groundwater. We see an acceleration of this land subsidence towards the presence. The delta is much lower elevated than previously thought. And if groundwater extraction is not restricted, it could drown large parts of the delta already within decades. So what we see is that only adaptation is no longer a viable strategy. So mitigation strategies to slow down subsidence are originally needed and especially focused on the extraction of groundwater. But we also see that the time or elevation to mitigate is rapidly running out. And I'll just give you this as the last one. It's a land subsidence is really a 4D problem. There's a strong link with anthropogenic land use. And we see that human use rates are much higher than men than natural rates. I'll skip this. I thank you for your attention. I mean, I'll go to part two with Saban. Thank you, Philip, for this very interesting presentation. I have absolutely learned a lot more about soil subsidence in the Mekong Delta than I knew before. So thank you for that. Very inspiring. I also saw that there are quite some interesting comments either in our live Facebook broadcasting and on our YouTube comments box, but please, participants, continue to submit your questions if you have some, do not wait with it because otherwise you might forget about it and that's what we wouldn't like. So thank you, Philip, for your very interesting presentation. And then we move on to our second speaker of today, who is Dr. Saper Eslami, a colleague of Philip in the NWO, Urbanizing Deltas of the World Project, Rise and Fall, in which he was also a PhD researcher. And of course, for the participants, if you have interest in the outcomes and the scientific outputs and the articles that has been produced in this project, please visit also their website if you go to your favorite research engine and you would type Rise and Fall, Urbanizing Deltas of the World Project NWO, you'll definitely find it. So let's continue to our second speaker. Saper is a fluvial coastal scientist and he's specialized in linking environmental change in deltas to climatic and anthropogenic drivers. And during his PhD research at Utrecht University, he's been studying the issue of salt intrusion in the Mekong Delta and disentangling the drivers of exposure and vulnerability. Saper is currently a senior advisor at Deltares and he's currently based in Singapore and he's also joining us from Singapore. And in this capacity is focused mainly on climate change adaptation studies and climate policy development in Singapore, as well as that he's actively working on developing mitigation and adaptation strategies for the Asian deltas. His presentation will be about the dynamics of salt intrusion in the Mekong Delta and with this having been said. Saper, thank you for being with us today and to share your knowledge with our audience and the floor is yours. Pleasure to be here, Jaap. Thanks for the introduction and I would say good morning, afternoon, and maybe evening. I see that there are participants from around the world. So I'm presenting this work that has been mainly done under the umbrella of urbanizing deltas of the world and within the Rise and Fall project that Philip gave a good introduction about that. I'm presenting the work but there has been significant contributions from a large number of people affiliated with different institutes throughout the six years, more or less lifetime of the project. So I would, I mentioned them and it's important that this, to know that this work wouldn't be possible without their contributions. I briefly touch upon the Mekong River Basin in this talk, talk about salinity and tides in the Mekong Delta and discuss the historical trends and talk about the outlook towards the end of the century and what we can expect for the Mekong Delta and close this presentation with some conclusions and lessons learned through the Rise and Fall project. Mekong River Basin in Southeast Asia. It runs through six countries, China, Laos, Thailand, Myanmar, Cambodia and Vietnam. It carries half a trillion cubic meter of water per year, more or less and plus minus 100 million tons of sediment every year. It's subject to extreme seasonality driven by the monsoon. For instance, in this picture, we see the northwestern monsoon with predominantly, sorry, northeastern monsoon with predominantly eastern wind. Here is the Mekong Delta. This is the Southeast Asia map. Here you can see India. Here is the Vietnam Mekong Delta. And this changes in the northern hemisphere summer to the southwestern monsoon with predominantly western wind. The northeastern monsoon coincides with brings about the dry season of the Mekong Delta when the river discharge is down to two, three, four, two, three thousand cubic meter per second. And the southwestern monsoon brings the wet season which can river discharge can reach 40,000 cubic meter per second. So there's a huge difference. Apart from that, the delta is existential to the lives of millions of people across Southeast Asia. And that has resulted also significant anthropogenic impact on the deltas. We see, for instance, there are already 13 completed hydropower dams along the main stream of the Mekong River. And there are something north of 300 operational hydropower and irrigation dams along the tributaries of the delta. Sand resources of the delta are very much wanted in the region for development and construction. And that has resulted in significant sand mining volumes across the river basin along the Mekong River. And if we look at the Mekong Delta at the end of this Mekong River basin, it's sometimes referred to as the rice bowl of Southeast Asia because of intense agriculture and agriculture that is going on in this delta. Delta, it provides 50% of the national food and it's home to more than 22 million people. It's no fun without some pictures. Philip gave an impression of the delta. Here I have a little bit more on, for instance, the rice plantations in the delta. The delta has thousands of canals over the entire system. Called navigation and irrigation canals. These canals are used for navigation and transfer of goods as well as extraction of water for agricultural and agricultural purposes. And this is an image of sand mining in the Mekong River. So if you fly over the Mekong Delta or if you sit by the river, it's inevitable that you would notice a large number of ships that are, barges that are moving some sort of construction material. So with that in mind, this shows a little bit the magnitude of the system. So this is an aerial picture of one of the, one of the distributor channels in the Asturian system of the Mekong Delta's main channels. See a small bar, actually a big barge that we're talking about two, three kilometer width of these channels, Asturian channels. If you look at the historical event, so this project of Rise and Fall started in 2015 and already in 2016 we faced reality with a huge drought event in the Mekong Delta. The UN situation report in 2016 reported during the event in the order of $250 million, the other loss of agricultural products. In 2015, at the same time, there were publications showing the effect of sea level rise and climate change, all the Mekong Delta projecting salt intrusion for the year 2050. That's in the year 2015. But in 2016, this drought event actually exceeded the projections of the year 2015. So that triggered a lot of questions for us. So where did suddenly that come from? How did science go so wrong within one year? So at the inception of the project, once we were expecting the drought event, we went to the Delta for measurements of the extreme event. This is our little, let's say, workshop in one of the villages in the Mekong Delta, in a parking lot of a motel room. This was our boat where we were going around with a fishing boat that we were doing measurements across the river, and of course, mangroves and palm trees are everywhere in the Mekong Delta. It didn't take so long that in 2020, again, another historical drought and salinity intrusion event happened that actually even surpassed by some measures surpassed the 2016 event. So it's like for instance, if you see this picture, one of these navigation irrigation canals that I showed the picture is fully dry. So the drought was significant and it's resulting salt intrusion has been devastating to the delta. That resulted, that was basically motivating a dive into the historical trends in the Delta and to understand what is actually happening because salt intrusion in the Mekong Delta is key to land use, basically the fact that what you can plant in these agricultural fields driven by do you have access to fresh water or not? That's why it's one of the main motivators of land use in the Mekong Delta. And there were more and more reports of increased salt intrusion in the Delta, not only the extreme events, but also complaints and complaints in the areas where they did not expect, they did not have faced salt intrusion historically. So what is salt intrusion if we cross an estuary and look at the river, the estuary, but this is more or less where the Delta is located and the ocean, we see that this salinity is a maximum at the ocean at the estuary mouth and then it decreases upstream towards the river and it's basically the competition between ocean forces being mainly tides, water level and wind for instance and river forces, which is basically just discharged that is pushing salt back and all these two are competing in a geometry and bathymetry, which is the geological condition that the estuary is located in. So any of these three that starts changing, you can expect that this salt balance between fresh and saline water is going to change. So to make it a little bit more vivid on the journey we had the last couple of years, that time, 2019, there was a BBC documentary that mentioned climate change, Vietnam destroying family life. I put it here and I come back to this in a few slides. So let's look at what happened historically in the Delta in terms of salt intrusion. So if we look at, for instance, this station, if we just look at the red lines, it's showing the higher 5% salinity measurements, stationary salinity measurements from the year 1997 to 2018. And if I associate one number per season, like the top 5%, I do see an increasing trend over the past 20 years. So there is definitely a trend, no question about that. Where is that? Well, we mentioned ocean forces and river forces against each other in a given bathymetry and geometry. So if you look at the freshwater inflow to the Delta, this is Quartier, so we're talking about 500 kilometers from the sea upstream in Cambodia, where we have the total dresses and discharge in black and the minimum dresses and discharge in gray from 1986 to 2018. And we also see that there is an increasing trend of freshwater over the last 35 years. And this is curious because that means that with, despite increasing freshwater discharge, we have increasing salt intrusion. So it's a bit counterintuitive. So that's not going to answer our questions. What about ocean forces? We look at ocean sea levels. Even without starting too much, we do see an increasing trend in the water level. So this is a tidal signal at this station at one of the mouth of one of the estuaries. And what we see is that, and if we, from the water level variation, if we extract the tidal amplitude, now we see that the tidal amplitude also follows a slightly increasing trend at the estuary mouth. So there's a question mark whether this is a relevant trend. But if you look at the tidal signal within the Delta, so at this station, this is 80 kilometers from the sea, 80 kilometer inlet, you see that there's still a strong tidal signal, very strong tidal signal in the Delta. In fact, the flow is going back and forth all the time in the Delta. If we look at that, even without calculation, we do see an increasing trend of tidal difference. And if we look at the tidal amplitudes, we see a huge variation in tidal amplitude. In fact, if we look at the actual trends until, let's say 2006, 2007, it more or less followed the same trend as the sea. But from this time on, the trend has been significantly increasing and almost total deviating from the sea level rise trend or the trend that can be associated to sea level rise. So this definitely can explain a lot and then we have to dig deeper into it. So if I go back to this documentary, BBC documentary, at some point it mentions about seven or eight years ago the weather changed drastically. This is a family that had to relocate from the villages of the Macomb Delta to Ho Chi Minh City to find a job because they lost their land to erosion. And they talk about seven or eight years ago that the weather changed drastically and associated that to climate change. In fact, if we go back seven, eight years back to when they talk about, they actually arrive at exact location when the tidal signal started deviating from the sea level rise trend. So we suddenly see this increase in tidal range that in our opinion is key to understanding what drives salt intrusion and higher water levels and the city flooding and river bed and bank erosion. So if we look further a little bit into data and look at the measurements, if you have a little bit of a background in coastal engineering, you might understand this and if not take it from me and then we can discuss this later. So for instance, we look at all these measurement stations in the Cong Delta. They are all water level measurement stations. What we do is that we calculate how long it takes for the tide to travel from one station to the next station. So from here to here or from this station to this station. So the distance it takes for the tide to travel to between these stations. And if I take this one, for instance, here we see the year on the X axis from 2000 to 2015. Actually it starts before, but 2000 to 2015. And this is minutes on the Y axis showing that it used to take something in the order of 200 minutes for the tide to travel from this station to this station. But that number started dropping from the year 2004, 2005 onwards. And we see that these downward trends are reducing the time that the tide travels between those stations, which basically means the tide is traveling faster. It's actually happening in all exterior channels. And if with a bit of a coastal engineering background that you know that the tide on travel speed is very simple as square root of gravitational acceleration type steps. So with depth increasing tide on travel speed increase that without measuring any river battle of all time we could conclude that on average the river battle was have been two to three meter deeper. And this was validated further in 2000 actually already this year. So without measurements of a direct measurement of river beds we could actually conclude that at that time from the tide of dynamics. And at that time there was already some measurements like for a cross section measurements that we also published it with our colleagues in Tokyo University between 2014 and 2017. There was each significant drop in river battle was at multiple cross sections. So this is not the entire but in the two of all the Delta all the Australian system but the some cross sections and we could already see for instance this one massive drop in depth of about 10 meters. And a note that these specific cross sections were known to be close to sand mines. So we did expect larger than two, three meter difference in these stations. But the average it's something in that order of three meters. So that brought us to this question what is the settlement budget of the Delta? So the pristine system used to carry 660 million ton per year. More recent estimates were 20 to 80 million ton per year. And with all these dams the expected efficiency of sediment trapping by all these dams it's actually up to 95%. So expected that in the order of 95% of sediment can be stuck behind the dams. And we have a sand mining of 30 to 50 million ton per year in the Delta itself which is the estimated we made ourselves based on all the sand mining licenses which was four times before four times more than the previous estimates. And we mapped those sand mining that sand mining estimates all over. And this is all legal estimates. So you can also expect some illegal sand mining in the Delta. That basically means that the sediment budget of the Delta is below zero. So from that we could immediately conclude that climate change is real. There's no question about that but what we face in the Macongu's environmental change and that if we look at increased salt intrusion as an indicator of that it's of course sea level rises three millimeter per year does have some contribution there. But we, Philip just explained that land substance is an order of magnitude larger than that which is mainly driven by anthropogenic processes. But also we have sediment trapping by upstream dams and excessive sand mining that results in river bed and bank erosion. And that also results in increased tidal range of 20 millimeter per year over the last two decades, 15 years more or less and two to three meter or 10 to 15 centimeter of river bed level erosion that also contribute to salt intrusion in the Delta. And this element is nearly five to 10% of the total salt intrusion increase that we've seen in the Delta. More than 90% of that is driven by upstream processes and processes within the Delta. So salt intrusion, higher tide, city flooding, bank erosion can all be associated to sediment starvation and which can be sand mining. It's driven by sand mining and sediment trapping. Here I would like to show you a little movie of... That we designed as an abstract video abstract of a movie that we just published, a paper that we just published. Let me see. So I hope you can see this all. Over the past few years, Ocean Saltwater has been reaching further into the riverine freshwater regions to make them Delta. I think there is a problem here with the streaming. Maybe I do it again. I refresh the page one second. Yes, now it's good. Over the past few years, Ocean Saltwater has been reaching further into the riverine freshwater regions to make them Delta. So what I choose to do is one of the major issues of the make-up that I've been up. Interest and freshwater supply to our agricultural land and the whole Delta ecosystem. In the Delta's many processes influence saline water intrusion. Among them, most importantly, ocean tides and two wheel discharge. And also other natural forces such as winds, waves, ocean search, precipitation and evaporation also influence saline water intrusion. On top of that, human significant distraints and natural resources of Delta's by agricultural water demand, sediment starvation, upstream dams and sand mining, groundwater extraction that leads to southern subsidence and climate change that could lead to sea level rise and upstream discharge anomalies. To implement measures against salinization and to predict the future, it is important to understand why we observe increased salinity intrusion. We did the field campaign to measure the salinity intrusion during the extreme event of 2016. We went out to measure the strong result intrusion in the Mekong ever recorded. The 2016 event damaged about 139,000 hectares and this cost about 215 million Vietnam. During spring and heat tides, we traveled upstream at 30 kilometers per hour at the speed of tidal propagation and measured vertical salinity profiles every three kilometers using connectivity sensors. A strong stratification difference was observed between neat and spring tide. We discovered that increased stratification during neat tide results in upstream salt transport while reduced stratification during spring tide stimulates salt flushing. In addition to the fieldwork, we developed the first Delta Y 3D model of the Mekong Delta and Delta 3D flexible mesh that integrates riverine, estuarine and coastal dynamics within one numerical domain. One of the primary findings of the modeling work was that ocean surge can increase salt intrusion by as much as 10 kilometer during the dry season and its effect can last twice as long as the surge duration itself. But perhaps the most consequential finding was that the Delta is extremely vulnerable to drought because of erosion, which is driven by sediment starvation. Erosion can be seen in the riverbanks or riverbeds. Incision of the riverbeds has increased stratification in some of the estuarine channels of the Mekong Delta. This activates 3D sub-processes that amplify inland salt intrusion. We have shown that if the riverbeds did not change over the past two to three decades, salt intrusion during the 2016 extreme drought would be significantly lower in some places as much as 20 kilometers. This is substantial evidence that suggests riverbed levels are existential assets to the livelihood and the way of life within the world's largest and most vulnerable deltas. So I stop, that one is finished and go back to the slide. Okay, so where do we go from here? So now that we have identified the drivers of change, we've seen that salinity is increasing. We more or less understand what is exactly happening in the system. Sea level rise of three millimeter per year, tides are rising 20 millimeter per year, river erosion of 10 to 15 centimeter per year. We know that fluvial discharge is changing, fluvial sediment supply is changing. We basically have an understanding of how salinity is driving inside. And we know that how subsidence has developed spatially varying over the entire Mekong Delta. We know that how it's going to develop in the future. How can we integrate all of this to understand what is happening, what is going to happen in the next century? So we could using the existing numerical models, we could integrate coastal and inland processes. We can basically integrate upstream and downstream processes. We have integrated climate change in anthropogenic drivers and climate change mainly in upstream discharge and downstream sea level rise and anthropogenic drivers mainly in subsidence and erosion, combining them all, basically integrating surface water and groundwater dynamics, which we used the first 3D hydrogeological model of Delta that Philippo already explained, as well as the first 3D numerical model of the entire Mekong Delta, surface water of the entire Mekong Delta, which for instance in this figure you see a little bit of a simulation along the seven main estuarine channels. For instance, you see that how salinity is changing with the rising and falling tide. So every lap is one hour, so these are one hour snapshots and how you see that salinity is an extremely dynamic process in a Delta X system. So with all this, we could actually integrate all of these processes to see how salinity would change, let's say in the next three decades, until the year 2050. And we have disintegrated for instance, what is the exact effect of climate change? So if it's only climate change, we can expect up to 67% increase in areas affected by salt intrusion. If we add land subsidence and different scenarios, we looked at two different scenarios. This percentage can increase up to 11%. And then we add river bed-level changes, then we see certainly a much more grave image that can lead to additional 36% increase in areas affected by salt intrusion in the scale of the Delta to make it a little bit more visual. So if we just look at climate change, we actually see that by the year 2050, most probably salt intrusion is going to be stable in Delta. There will be increase, but it will be stable. If we only look at climate change, if we add subsidence, two different scenarios of subsidence, subsidence can lift this further up at another 5% to 6%. But perhaps the biggest threat to the Delta in terms of salt intrusion is in the river bed-level changes. And if we add extreme sea-level rise, so we know that sea-level rise is accelerating faster than it was previously estimated. So if we also add extreme sea-level rise, it's a 60 centimeter by 2050, all these lines will be lifted much further higher. So it's a very complicated system and we had to do a lot of more sensitivity analysis to show how many of these environmental pathways can be expected for the Delta. So this brings me to my conclusions that basically in the short term within the policy scope of two to three decades, anthropogenic drivers determine the fate of the Delta. Beyond 2050, perhaps climate change and relative sea-level rise, depending on the policy development would perhaps take over the issue of salt intrusion in the Delta. There are challenges and opportunities. The challenge is that many of these processes can be irreversible. And the opportunity is that a lot of them are man-made. So we can, by effective policy-making, we can influence some of these trends before there's no point of return. The rise and fall project as a whole had significant policy implications in Vietnam. It basically shifted the narrative on the Macomb Delta from the discussion on the climate change towards anthropogenic drivers. We managed to show that anthropogenic drivers overtake the existing unwanted trends in the Delta and this has shifted the narrative over the last five years. The mitigating groundwater extraction and sand mining and drain-stating flooding as a mean of sedimentation has been taken up by the government as a policy. There are various initiatives and, let's say, spin-offs from the project to, for instance, support transforming farming practices in Delta, like going towards mixed rice and ecocultures. So it's more of an adaptation rather than medication. We have to adapt. There will be change that's going to happen. So how can we adapt to the situation and we're discussing, for instance, what mixed systems of rice and ecoculture? And perhaps the main implication, in my opinion, was that we have to look at integrated solutions through a systems approach because if we look at incremental change or if we look at individual problems, we probably cause another problem somewhere else. As an example, if we look at, we know that there is riverbank erosion in the Delta and if, let's assume that we come up with it without understanding the entire system, we look at one single solution for stopping riverbank erosion at a certain area, like in a local level, we perhaps not doing anything but spending money and basically migrating the problem to another part of the Delta. So understanding this integrated image is extremely crucial and it's not only the Delta, but it's the entire system, the river basin. We have some lessons learned for ourselves within the project. We know that technological advances be it numerical models, computation, capacity, instruments and all that, they can help significantly and what we have done, for instance, in the last five years, it would be impossible 20 years ago. Data and local network are fundamental. Without actual data, we would not be able to carry out any useful scientific research, honestly. And the local network and the local support we have was extremely crucial in whatever we did. Complexity of the Deltaic system requires critical science and that means that the system is so complex and it has so many drivers that simplification of the problems does not necessarily help solving the problems. And it needs really critical look into all different aspects of the system because it's so much vulnerable to any change. And by overlooking this complexity, we might overlook, we might miss a lot of insight into that. And the last thing, research update, of the Rise and Fall project require critical science and local presence and proactivity over the lifetime of the project and beyond, because we are still both really active in the policy implications, policy development of the Delta. And that brings me to the last lessons learned that looking at this picture from the first Urbanizing Delta of the World Workshop in Ho Chi Minh City, that we have to enjoy life as much as possible before there is a global pandemic. I'm hoping that we can all meet again anytime soon. Thank you very much for your attention and we can move on to the questions. Thank you, Sper. I really enjoyed your presentation, very insightful. Also in relation to the presentation of Philip and how this relation is between soil subsidence and soil intrusion, but also some of the other aspects that have an influence on that, have an influence on soil intrusion and soil subsidence. I would like to thank all the participants as well for submitting your comments already in the chat box. And I saw with one of my eyes that there was already a lively discussion going on. So thank you, Philip, also for already answering some of these comments in the comment box. But I would like to continue and we have only a few, not so many minutes left, but I think the title of this master class is Getting Grip on Sinking, Shrinking and Saltier Deltas. And then there have been several comments or questions either on the Facebook comment box or the YouTube comment box on policies, on what can we do, adaptation versus mitigation measures, and also what can other deltas in the world maybe learn from the lessons that you have seen here. And so maybe in relation to Getting Grip, can you maybe give some insights already on what you already see now? Is there an urgency felt among local policymakers in the Mekong Delta? So are they trying already to get grip? Are there maybe already some good examples? And also what do you think for the future? There is, for example, the Mekong Delta plan that also proposes a certain kind of agrobusiness development. There are of course other development plans also in the area. So maybe first, Philip, maybe you could share some of your insights on this. So I think the, let's say the end conclusions that Saper presented for this master class, they are echoing in this a lot. So there's really this shift in the last couple of years with the, let's say prime focus on climate change and the problems induced from that. And now also seeing there's actually environmental change which is partly driven by humans. And that should also be taken into account because it's actually creating more changes at present. And this is, there's really a rapid shift in terms of realization happening in Vietnam. And there's now, there's a number of this, national policies even recognizing this, for example, there's now all the provinces in the Delta are now working on the plans to create groundwater protection zones with actually the focus to limit land subsidence and sanitization of the groundwater. And this is something that really was a couple of years ago was not happening because it was not simply not on the radar. So there's, I would say there's a lot of effort going on and the changes in realization are really going fast. So that gives myself at least a lot of hope. And what we see, for example, this Mekong Delta plan which the first version was from 2013, that in that plan, you also see this, let's say, the issues of land subsidence, for example, was mentioned but it was also mentioned we don't have a lot of data on it, so we don't know what we should do about it. But now, I mean, in the new plans, this is at least from the Vietnamese government that this is really getting a more and more prominent position. But we saw that certain agricultural developments have a stronger impact on soil subsidence. And I think some of these proposed agro-business developments might actually induce more soil subsidence with my limited look on it. So how would that really? It's basically a question, let's say, where is the water coming from? And in the last decades, let's say the whole development of the Delta is in a way fueled by two basic things, which is one is fresh groundwater and the second is sent from the river channels as Saper talked about. So these two basic, let's say commodities, natural resources are being overexploited and that is causing a lot of the issues that we talked about. So basically you have to search towards development of your agro-business system or any other system that is not causing overexploitation in either one of these two resources. And that may mean that you actually have to maybe downscale your productivity or find technical solutions that are actually allowing you to keep up, let's say, high productions, but not exhaust these resources. Yeah, and if I may add on the agro-models, the agricultural models that are being proposed are now being informed by all these trends and especially understanding the spatial variability of the trends. And that feeds to how you're going to develop your agriculture model. How do you develop your cycle? How to maximize, for instance, sediment intake? How to not use groundwater? Basically groundwater used for agriculture even right now is forbidden and it's mainly used for agriculture because the volumes of water for agriculture is just 40, 50 times larger than what is being used in the groundwater system, but the groundwater has a significant sensitivity, its extraction on land subsets. So that's one of the impacts and one of the important conclusions that it's not about that agriculture, you have to stop agriculture, but you should just do it smarter. Perhaps use the technology that is available but also understanding the system, develop your system in a way that is not consuming your natural resources and even maybe recovering part of your trends. On another point you mentioned YAP and the implications for other deltas, these trends that we see in the Mekong Delta it's not only the Mekong Delta. At least in Southeast Asia, we see a lot of these trends. In Ganges, Brahmaputra, in Erawadi, in Chowpraya, in Pearl River, in Red River, similar trends have been seen, maybe in one of them more subsidence, more or less salt intrusion or sand mining, but it's like there is a proportion of the problem driven in all of these deltas, a large proportion of problems driven in all of these deltas with the same processes, dams, sand mining and groundwater extraction. These three are driving the main changes in the Mekong, in the deltas, in the region and around the world, which basically means you need similar in-depth studies for each of these deltas to be able to develop effective policies. Yes, thank you. And I was indeed also very surprised to see also indeed the differences that you found in your studies in comparison to earlier studies on the land elevation from the river at that depth. So that also was very insightful, I think. What I think is also an interesting point you mentioned and it relates, of course, to the sediment trapping in dams, which is of course a very urgent issue also in the Mekong with all the proposed dam developments. And I think that is also something that we see in other basins around the world, especially also with the revival of hydropower. And how would you see the international cooperation here in the Mekong river community? So there is an ongoing strong debate between the basin countries. So the Mekong river commission is, let's say, the coordinating body between the lower basin countries. And China is not part of that. China has its own policies, but all of these conversations are ongoing. For instance, while there was a peak in increasing dam development, hydropower development, especially along the mainstream, the impact of that is already seen in the hydrological cycle of the river. And its impact has been actually part of what's happened with salt intrusion in the delta over the last couple of years. Having seen these, for instance, Cambodia has stopped its hydropower plants if I'm not mistaken, 2019. And they also had their plants in hydropower development. Laos is under a lot of pressure by the lower basin countries to stop their hydropower plant development. But it's an ongoing debate. The interesting thing that our research shows because the discussion of upstream riparian countries and cross-boundary issues with these rivers is quite old. And in a way, in the past, it's been either looking downstream, let's say, sea level rise, climate change, or upstream dams in the basin. But not really looking into your own background. And I think what our research really showed is that a lot of the changes that are happening are actually caused by activities that are happening at the local scale. Not all of them. Of course, there's especially when you go to salt water intrusion and sediment dynamics, there's a big upstream component. But there's also a big component actually happening inside your own geo restriction. So, yes, it's important to talk as a basin, right? But it's also important to realize that you have actually some control and quite some control just by managing your own, what is inside your own geo restriction. And what is very important is this integrated systems approach that Saper also mentioned. So, not looking at the individual aspects as it's been done, let's say, classically, but really crossing borders of disciplines and not just, let's say, guys like us who studied the physical system talking to other guys who studied the physical system, but actually creating this really integrated approach where we connect and combine also, let's say, all the human aspects and dimensions into this, let's say, the road toward solutions because this is the only way that we can create, let's say, we can sustain a liveable system in these deltas. Yes, thank you, Philip. I think that proper message been shared with all the audience and I think also the general message in relation to climate change mitigation and adaptation. It's easy to look also at others, but also look at yourself first. We are at the end of this master class. I already hear the church bells ringing in the back, so it means that it's 11 o'clock local times, which is time to end this session. So I would like to thank you, Saperre and Philip, for your very interesting presentations. I really think also our audience have enjoyed it and appreciated it very much and it shows that there is also already a lively debate. I'm inviting you to have another look at the comment box and give individual replies to these participants. I think that would be appreciated very much. So thank you. Then I would like to invite also, of course, all the participants to join us again next week, because next week we start at the same time. So on Wednesday 22 September 21, we start again at 7.30 GMT, that's 9.30 in the Netherlands, with Dr. Sanjayan Nat and Badrul Hassan and the topic of our master class will then be thinking about complex urbanizing delta systems. So thank you, Philip. Thank you, Saperre. Thank you, all participants. Also, thank you, Leon, Shanur and Laura, who supported us on the back of this master class. Your help was much appreciated and I'm looking forward to seeing you online again next week. Thank you very much. Thank you. Thank you. Bye.