 I'm going to use an example, basically, because the introduction was already made. So when we talk about clean energy, what are the constraints and what are the opportunities? Because nothing comes for free. And I'll use an example of the Nile. And I just call it a stressed, trans-boundary river basin with challenges and opportunities. And I'll use just this example so that we can discuss what the consequences of these things are. The African countries, of course, with the support of the developed countries have recognized that infrastructure development is the opportunity for Africa. And there is the so-called PIDA program, which is the program for infrastructure development in Africa, which deals with transport, with hydropower, with water supply, and so on. And this PIDA program is envisaging to achieve by 2040 an interconnected continent. And there are nine dams planned, big dams, and five smaller dams. But overall, when you see the potential of Africa, you have potentials of a capacity of about 54 gigawatts, which is a huge number. In order to achieve that, you have to build thousands of kilometers of transmission lines. And you have huge storage potentials that you have to use for that. This just as the macro scale of what you can do in Africa. But as I said, I'll show you that there are challenges with that. Most of the river basins, where you would build the hydropower plants, those river basins are trans-boundary. So anything you do upstream will have impacts downstream. You see here the bigger ones, like the Nile. You have the Niger in West Africa. You have the Zambezi in Southern Africa, which cover about minimum of nine countries, up to 13 countries that you need to handle in an integrated manner at the political level. So I will not talk about the political level. I'll talk about just the physical side of the issues that will have to inform our politicians and our economists to come to a sound information-based political decision. So there is this UN Water Courses Convention of 1997, which tries to handle these issues. And there are some articles, too, I've highlighted here, that need consideration. One is, I just call it, the right to development. Every country has the right to develop, and it is formulated, as you can see here. And there is the other issue of defending existing uses. You don't want to cause any significant harm to neighboring countries when you develop yourself. Basically, in the water sector, it's an upstream-downstream thing, but it mustn't necessarily be the case. These issues are also across sectors. Let's say you develop hydropower, you may damage irrigated agriculture, and vice-versa. So it is the transponder issue is one thing, and then the sectoral issue is the other. I'll come later to the issue of, of course, ecosystems as well, because they also need to be considered. So before I talk about the Nile Basin, this issue, this example that I'm going to give you, you have that on the Zambezi, you have that on the Niger, you have that in any river basin in Africa, where you have, as I said, some kind of a conflict of interests, not necessarily a win-win situation. You may have win-lose situations, and they need to be identified. And I'll show you an example where we have tried to identify these win-win and win-lose situations that will inform us to identify the corridor where we can, where we can understand what the implications of decisions are. So for those of you who don't, are not very familiar with Africa, basically United is the longest river in the world, but sometimes people say it's also the Amazon, but anyhow it's a very long river. It covers about 10% of the African continent. There are 11 countries in the Nile Basin with more than 400 million people. And within the basin we're talking about a magnitude of 200 million people. These are the countries, people think when you think about rivers it's basically the main river, but when you see the whole catchment countries like Burundi, Rwanda, highly densely populated regions, countries like the DRC, although it's a small part, they are also part of the Nile Basin. Everything you do there will affect the equilibrium of that river system. We are in the climate change discussion and irrespective of climate change, only due to population growth and other aspects, the Nile is a waterscast region. As you can see in this map, you have physical scarcity in a country like Egypt. In the other countries you have economic water scarcity because the water infrastructure is not developed. So we have, and this will change over time, it will be aggravated by climate change and also by population growth as well. So the challenges that we have on the Nile is we have droughts. We have this high variability of climate in the Nile Basin. It's basically simple, like Joseph's dream, seven wet years, seven dry years, these patterns we can see from those few time series that we have. We have floods, we have environmental degradation and as we are in, like in most African countries we have poor coverage of water supply and sanitation. And based on that, most of the economies, for example, like the economy of Ethiopia, there is a clear correlation between the GDP and the rainfall patterns. So there is a huge food insecurity if you have consecutive dry years, these countries don't have the resilience to secure food for the people and power shortage. Those of you who have lived in Africa or have visited African capitals, it is in every day's life you can see there's power shortage. The opportunities in the Nile Basin, like in also other basins like in the Zambezi, but also in the Congo Basin, is you have a huge untapped potential for energy. You have also untapped potential for food production. And I'm always optimistic to say there is the political will for cooperation, although sometimes the media tells us that there are conflicts and the conflicts are part of that will for cooperation. But I think gradually our politicians, our decision makers are understanding that we have to cooperate. Now I come a bit to the hydrology of the Nile. The total runoff is 85 cubic kilometers. It may sound a big number, but when you project it on the population that you supply, it's a very small number. Basically the Nile is a river which is, it's a dry river you can say. You have 85% of this comes from a very small area basically from the Ethiopian highlands. And compared to other big rivers, it's really a waterscass river because you have on one hand the high seasonality, meaning you have dry season wet seasons, and then you have the inter-annual variability also. I'll show you some charts about that. And as I said, 70% or as I mentioned, 70% of the flow occurs between August and November. For example, this shows you the pattern of the Nile over the year. So as you can see, most of the flow occurs in summer of the northern hemisphere, shifted by one month, and most of the water comes from the Ethiopian highlands. And as you can see in most of the year, the water flows very, very low. And I'll show you a similar picture later. You have here those times around the beginning of the 70s. There was a dry year, and then you have some consecutive dry years from 82 to 86. Some peaks high flows in the 80s, 90s. And this is the annual influence of high Aswan Dam. And as I told you, the water there is influenced by the rainfall pattern in the Ethiopian highlands. I'll come to these circles. You may please try to remember what happened in those years in that part of Africa. I'll tell you the answer to the quiz later. The major subsystems of the Nile, I'm telling you this story so that you understand, building a dam, you have to understand how a water system behaves. So basically you have four systems in the Nile. You have the White Nile, which is originally South Lake Victoria. You have the Blue Nile and its tributaries, which originates in the highlands of Ethiopia. You have the South Swamps in Southern Sudan and South Sudan, which is a huge swamp, one of the biggest swamps in the world that basically swallows all the water that comes from Uganda and from Lake Victoria and gives only half of it downstream and the other half evaporates. So the swamp grows and gets smaller. And then you have the Main Nile, basically where you don't have any water coming in, basically where the river just flows through the desert for, I don't know, how many thousand kilometers. And this on the left side, it shows you basically the thickness of the line shows you the magnitude of the water in the river system. So I'll go quickly through some key characteristics of the countries. We have the Nile in Egypt, where 99% of the water comes from outside of Egypt. We have the agricultural economy and the livelihoods of the people fully depend on the Nile. It is fully regulated by Hassan Dam. And you have in Egypt, of course, it's a middle income country. It is a highly developed water resources infrastructure. So the main challenges are you have a decline per water capital availability. So water quality is deteriorating, sea level rise, which leads to salinization of the soils in the Nile Delta, which is severe for the Egyptian farmers. And then when you come to Ethiopia to the Blue Nile, you have complete other characteristics which were, I told you, the highest seasonality. But you have land degradation is a huge issue. You have high sediment loads, high erosion. And on the other hand, the opportunity is you have huge potential for hydropower development and for flow regulation. When we go to the Sudwekt Lands, that was the yellow circle in the middle. You have, I think, the second largest swamp in the world. It has a very complex hydrology that we still don't understand. And half of the water evaporates. And it is home for endemic fish, birds, for animal movement and plants, very unique plant ecosystem. And it's also a major source for fishery in the region, for livestock, and for water for domestic water use. Its development is very low. So but still there are some ideas to develop infrastructure there. And I just mentioned one thing here at the bottom. There is a major interest to conserve water loss by evaporation, by building a canal around the swamp. That would secure for downstream, meaning Sudan and predominantly Egypt, would secure water supply. But on the other hand, it would dry the swamps and it would have most likely very severe ecological impacts, which is very difficult to investigate. We don't know all the consequences that this would cause. So it's about trading off what we would get something, but we may lose something else. Lake Victoria is more or less because it's cut apart from the Sud in southern Sudan. It is an own, it can be regarded as an own water river basin. And basically there you have issues that do not diffuse downstream. But anyhow, millions maybe are a magnitude of 100 million people or 80 million people depend on the water systems of the Lake Victoria region. So these are the development potentials. Basically you have hydropower development potential in the Blue Nile system. You have in the downstream in Egypt, you have the potential for irrigated agriculture to make it more efficient. And in the Lake Victoria region also you have a huge potential for irrigated agriculture. I have highlighted the Sud and the confluence of the Blue Nile with the White Nile also for irrigated agriculture. So basically you can say, apart from the highlands of Ethiopia, you have irrigated agriculture as one opportunity and in Ethiopian highlands hydropower. And this is not necessarily a win-win situation, but because we have a distinct system, in this case the developments in Lake Victoria region in Ethiopia don't have big influences to each other on one hand. And I'll show you that hydropower development on the Blue Nile does not have significant impacts downstream, which is of course subject for discussion later when we come to the discussions. The key issues in the Nile basin, basically I've mentioned that, so let me go over to the next slide. Storage. Storage is not only in the power world very important, it's also in the water world very important because storage makes you more resilient to the variabilities that you experience in rainfall. And it will buffer the droughts and so building dams makes you more robust in any ways. It's not only in the water, in the water world like that, it's in the power world and even in economics it's the case. The bigger the buffer is, the more robust and resilient you are. So I'll try to make this now in the last five minutes. An example of a development of a dam called the GERD, which is the Grand Ethiopian Renaissance Dam, which is being built not far from the Ethiopian side. Please see the magnitude of the storages. It has about 74 cubic kilometers of storage and then in that system downstream up to, until you get to Egypt, you have relatively small dams ranging from four to eight cubic kilometers. That cannot even buffer the flow that comes in the rainy season in Ethiopia for two weeks. They cannot even buffer that. So basically currently you only have the downstream, the highest one dam buffering a magnitude of two and a half years of water. And now in the Ethiopian highlands a dam is being built. And you may know from the media that Ethiopia, Sudan, and Egypt are discussing issues around that. It's a big dam with six gigawatts installed capacity and the average annual energy is estimated to be 15 terawatt hours. So I come to this chart again. We did some modeling and climate change. We, when we talk about climate change, we assume that the future is not like the past and you have lots of assumptions. So we did the modeling for what would happen if we have the GERD and the highest one dam in the Blue Nile system. And we used the time series from 1911 to 2003. So the question I asked at the beginning, 1972 was the first famine in Ethiopia that led to the revolution and the coup d'etat. Then we have from 84 to 87 where we had this huge famine again in Ethiopia. And then that one, 1988, was the catastrophic flood in Khartoum. And then just almost a decade later, another huge flood in Sudan. So you can see the inter-annual variability is very high. The water ranges from 20 billion meter cubes in the dry years up to 70, a factor of 3.5. So buffering is very important. So if we build one day when we start producing energy in the GERD, what would happen? Let me explain that to you with this slide only. The black line, the energy at the highest one dam without the GERD tells you that in average, currently in Egypt, you can produce about 6.2 terawatt hours per year. This is a duration curve telling you probabilities. And in 5% of the time, you can produce more than 6.2, up to 9 gigawatt, terawatt hours per year. And then in those dry years, 10% of the time, you produce less down to 2. something terawatt hours per year. If you build the GERD, because you have buffer upstream, you would have a lowered energy production in Egypt. In those years that are very wet, you would still produce a constant amount. And then in the dry years, you could produce more than in the dry years now. So you have to understand that when you build dams upstream, the consequence would be, without going to details now, is that downstream, you produce less energy. But you will produce upstream in a magnitude of about 15 terawatt hours per year at the GERD, where the variability is much higher. As you can see, it's between 8 and 22 terawatt hours per year. And when you sum them up, we are going to have about 20 terawatt hours per year, the two systems. So it's important to see that upstream developments with their adverse impacts that you produce less makes the system more smooth. This is a chart maybe that has impressed me most. Basically, I want to draw your attention to the black line and the red line, which compares the evaporation of the Lake Nasser without the GERD, which is in mean about 9.4 millimeter cubes per year, which is a huge number. And then you build a dam upstream, you increase evaporation upstream, which leads to the situation that downstream you get less evaporation. And system-wide, the evaporation is the same. And this discussion is still ongoing between the three countries, what the adverse impacts are. And basically, to make it simple for you to memorize, you buy with evaporation, you buy basically energy, you can say that. It's not fully correct, but it's like trading evaporation. But there is another adverse impact for Egypt as well. It's about water supply deficit. The black columns show you if the GERD is not built, what the water supply would look like. So you have high peaks, and then over decades nothing happening. When you build a dam upstream, what would happen is you would have less severe deficit, but more often. And when we modeled that, and I need to mention that here, we maximized energy production upstream. What would happen if we didn't maximize energy production? Let's say we would have put in a rule like release water, produce less energy if you have a dry year. Then maybe what would happen is in those years, in this case in the 40s, where you have water supply deficits, maybe you could reduce that. This is subject to investigations in the future, but this is even if you maximize energy upstream, which is the worst case for downstream existing infrastructure, you would have reduced peaks, but more often. And economists need to analyze what does it mean for a national economy. This is a summary of, maybe I have said that already, so let me tell you the key messages now. This example is an investigation of modeling work that we did. Just a simple shot for seeing the interest of one upstream country, how it affects the two downstream countries. And that has shown us that the effects are significant. However, they can be lowered if we incorporate, let's say, release rules that consider downstream activities. The three key messages that I have here are basically climate variability and uncertainty in the Nile Basin will increase due to climate change. And as you know, as you have seen, we already have in East Africa, and this is one of the most variable regions in the world where you have high seasonal and intranol variability, and climate change will enhance that. Interestingly, I'm not a climate scientist, but when I discuss with climate people, they tell me it's either wetter or drier. They tell me it's either hotter or warmer or colder. But we as hydrologists cannot do anything with that. We just produce ensembles and do the models with that. So East Africa is, from the climate point of view, not a trivial region. More reservoir storage capacity helps mitigate impacts. We just did this one small example. We're currently at the Nile Basin. We're investigating even building more dams to what would it lead, what would be the impacts on that. And it is for us already evident that when we do that, we have to see across the borders. People tell us, my predecessors talked about green energy, building hydro and so on. The moment you do that, this will lead to a transboundary cooperation. Like I just mentioned, when you operate a dam, you cannot only operate it for maximizing energy or maximizing yield from agriculture. You may have to trade it off against producing less energy in order to reduce the downstream adverse impacts. That's in a nutshell what's happening on the Nile and what that region is trying to do when it comes to green energy. Thank you.