[00:00:00] Bridget Scanlon: Welcome to the Water Resources Podcast. I am Bridget Scanlon. In this podcast, we discuss water challenges with leading experts, including topics on extreme climate events, overexploitation, and potential solutions towards more sustainable management. Today, our guest in the Water Resources Podcast is Günter Blöschl, who is a professor at the Vienna University of Technology in Austria and is a globally renowned hydrologist and has worked a lot on flooding issues. He has received numerous awards during his career and was elected to the U. S. National Academy of Engineering in 2020 for international leadership in prediction and management of extreme hydrological events.
Thank you so much, Günter, for joining me today.
[00:00:56] Günter Blöschl: Thank you very much for the invitation. It's a pleasure to be with you.
[00:01:00] Bridget Scanlon: So Günter, I think it would be nice to begin the conversation. We will cover a lot of things today in this podcast but covering both the causes of flooding at regional to global scales, and you have done a lot of work in Europe, but also globally, and then looking at, with a deeper understanding of the causes of flooding, then we can develop better solutions considering both nature based solutions and engineering solutions. I like your work also on social hydrologic aspects, so looking forward to covering those different issues. But maybe we can just first start with recent flooding in Bologna in Italy in May this year and also flooding in Germany in the summer of 2021 with almost 200 fatalities in Germany. Maybe you can describe a little bit about those floods and your understanding of them.
[00:01:56] Günter Blöschl: Yeah, there have been a number of major floods in Europe in the last years. One of the outstanding ones is the flood in Germany two years ago, which more than 200 people killed, as you said. This event was very unexpected. It was not so unexpected in hindsight, but at the time the event started, there were forecasts, but then for a number of reasons, the flood was not managed in an ideal way. And as a consequence, there were so many fatalities. The event in Bologna was similar in that even though there were fewer fatalities, it was unexpected because there was an event only half a year before. It was a very similar event in September, October 2022 in Emilia Romagna. And now only a month ago, and almost similarly, a huge amount of damage. So these are events that appear to be quite unusual, but they seem to happen all the time.
[00:03:02] Bridget Scanlon: Right. And of course, we're no stranger to floods in the U S either in this year, atmospheric rivers in California, resulted in widespread flooding in that region. beginning in December 22 and then extending into January 23. And at first it was because it ended a major drought that had lasted for a few years, it was welcomed. But then as we had a sequence of atmospheric rivers coming, a family of them, then it ended up causing some flooding issues and concerns about that. So, with the atmospheric rivers, you mentioned, the unexpected nature of the floods in Germany and in Bologna, in Italy, with the atmospheric rivers, they can see them coming across the Pacific. And so they really have a good forecast a week out. And so in mid-December, then they were tweeting and reporting on projected issues in around Christmas time. So that gives them a good, at least a seven day lead time, but it's difficult to manage without that. I guess maybe we saw similar issues in Australia in 2011 after the long term, the millennium drought in Brisbane, Toowoomba, with about 20 fatalities flooding in that region, and they had been going through a drought for more than 10 years, and then the flooding. So, that, that psychology is difficult to manage also, right, for water managers.
[00:04:32] Günter Blöschl: Yeah, these situations all put flood management in a difficult situation for different reasons. As for the flood in Germany two years ago, it was a flood that was much bigger than they expected. And also there were issues with the communication and there were issues with the flood hazard maps that in hindsight were not perfect.
In Bologna, the unexpected thing was the quick reoccurrence. Also the case of the Brisbane flood in early 2011 was unusual, a flood immediately following a drought and there was this additional complication that flood managers really were keeping the reservoirs full because they were concerned about strengthening droughts in the future. But this was a reservoir with multiple purposes. On the one hand, a reservoir to take up the flood waters. So you want the reservoir to be empty at the beginning of the flood. On the other hand, another purpose of this same reservoir was water supply in cases of water scarcity. And then, because they kept the reservoir full, they were in the worst possible situation at the beginning of the flood, triggered by the psychology of the concern for a drought. So, they're all difficult situations for flood managers to deal with. Right,
[00:06:05] Bridget Scanlon: The last thing you want to do after going through a 10 year drought...is to release water and then people say, Oh my, why didn't you keep that water? Because we're still in the drought, but that ended the drought. And I think the U. S. Army Corps of Engineers is becoming more aware of these issues and trying to look at forecast informed reservoir operations in the U. S. And so they can consider what the projected climate is and then manage, try to manage the, optimally manage the reservoirs.
[00:06:38] Günter Blöschl: Forecasting systems exist. These forecasts are more accurate for larger river basins and for shorter lead times. The smaller the reservoirs, the smaller the catchments, the harder it is, and the longer the lead times, the harder it is.
[00:06:53] Bridget Scanlon: Right, right. So, Günter, we hear a lot these days about climate change, increasing temperatures, and the increasing water vapor holding capacity of the atmosphere, and causing rising precipitation intensity and increasing flood risk. Can you describe, because that's just considered gospel now, and maybe that's not equally applicable everywhere, and maybe you can describe more detail on that.
[00:07:25] Günter Blöschl: Yeah, when we talk about flood estimation, for flood forecasting, there are really two main types of forecasts or predictions that are done in hydrology as needed for flood management.
- The first one is the one we referred to in the case of the Brisbane flood or the atmospheric rivers. It is flood forecasts with a lead time of a couple of days or weeks, where we know for a particular time and date, a probable flood discharge water level. This is one basic application of engineering hydrology in flood management.
- The other application is a little different. It's flood risk estimation or flood hazard estimation, where we are not interested in the exact time. The flood occurs, we are only interested in the probability of a given flood discharge or a given flood water level. And this is not used for emergency management evacuation as the first type, but that's what used for planning for design of infrastructure and for flood risk planning for insurances.
So these are the two main tasks in engineering hydrology regarding flood estimation. Now for the second type, the flood probability estimation, concern is - given climate change - that floods of a given probabilities will increase and what are the possible reasons? Of course, rainfall is the main driver for extreme floods. And there is a physical law called Clausius Clapeyron relationship, which states that as the atmosphere warms up, the water holding capacity of the atmosphere increases. Precisely one degree of warming will translate into an extra water holding capacity of 7%.
On average in the northern hemisphere, now the air temperature is 1.5 degrees higher than it was 40 years ago. And so you could say higher water holding capacity and therefore the potential for large rainstorms should be increased by 7%, 10% and even more. Now this is true, but this is only one of the effects of a changed climate. It's the thermodynamic effect, but there is also another effect which has to do with the changed atmospheric circulation, and the change to atmospheric circulation means their flow patterns. The storm tracks have changed because of differential heating. The North Pole region is heating more than the equator, and therefore the storm tracks are shifting, perhaps moving more slowly.
This is the more dynamic effect. Now we know that both effects are relevant when we actually look at changes of floods. On the basis of flood observations, discharge observations on the ground, we see that in many parts of the world, the floods do not increase. And why is that? Even though the temperature may increase everywhere, the floods will not increase everywhere.
And the reason for that is that the atmosphere is not always saturated. So it is true the Clausius Clapeyron relationship applies. But it is not always relevant because the atmosphere is not always saturated. And also this is only the rainfall side and floods are not equal to rainfall. Look, the rainfall translates into runoff modulated by soil moisture, evaporation, snow and lots of other processes.
So the summary of this is that yes, warmer temperatures translate into larger water holding capacity, but this is not always relevant, only in some regions of the world.
[00:11:34] Bridget Scanlon: So some of your work, Günter, you talk about that Europe is currently in a flood rich period, and you looked at these periods over the past 500 years, that was a very interesting analysis. And, considering when in the past we've had these flood rich periods and how the current flood rich periods compares with those.
[00:11:54] Günter Blöschl:. Yeah, we did an analysis on the basis of historic archival data for many places across Europe in the past 500 years. The analysis of written records or text records, where we get information about the magnitude of floods. The analysis was published in Nature, two years ago. What we find, as you said, the last 10, 20 years were flood rich as compared to the context of the last 500 years. But this is not the only flood rich period in Europe. There were lots of other flood rich periods, the most prominent one was in the little ice age around the 17th, 18th century.
It was a period where floods were even bigger and even longer and more widespread than they are now. And the interesting thing, which also relates to the question of Clausius Clapeyron, is that in the past there was quite a clear correlation between the air temperature during a given period and the propensity for flooding. The flood rich periods in the past in Europe were significantly cooler than the flood poor periods. Which means, yes, the Clausius Clapeyron relationship applies, but there are other processes that come in, and in the past, the colder periods were the periods with more rainstorms and with bigger flooding. The last 20 years are an exception because they were much warmer than essentially all the periods in the past 500 years because of climate warming.
And so the mechanisms have changed. We have a warmer climate and a trend that deviates from the past and more floods because other mechanisms kick in, such as change to storm tracks, which we can observe.
[00:13:54] Bridget Scanlon: I really commend you on pulling together such a long record and trying to put the current issues within a long-term context, because that's often what we lack.
And it's really important, I think, to contextualize the current situation. You have done some excellent work on looking at causes of flooding and I really enjoyed your paper in HESS where you examined three different hypotheses related to flood generation mechanisms, land use change, hydraulic structures, and climate change.
Maybe you would describe that work for us a little bit, Günter. I thought it was excellent.
[00:14:35] Günter Blöschl: Yes, thank you. When we look at flood changes, that is, how the probabilities of a given flood or a discharge of a given probability changes, there's not just climate change, there are also two other factors for changing river floods. The first is land use change, that would be urbanization, for example, or more heavy agricultural machinery, or it could be deforestation.
So these are the three main land use land cover changes that would affect flooding and potentially increase the flooding. It is to say that deforestation mainly affects the small floods. The big floods are not so much affected because the storage capacity through which vegetation mainly operates in attenuating floods is quickly exhausted with large rainfall amounts.
When you plot the change in flooding against the flood magnitude, you will see for small floods, there's a big effect of afforestation, deforestation, and this effect essentially diminishes as the flood becomes huge. And the corollary of that is that afforestation, planting trees, maybe a very good strategy for ecological reasons, certainly biodiversity has many positive effects, but it will not help in reducing the flood risk of rivers because it mainly operates on the small floods and mainly in small catchments. Similarly urbanization, and heavier agricultural machinery is particularly relevant for small catchments, a couple of hectares and square kilometers. As we go up in catchment scale, we can see from the data that their effects diminish. This has to do with the way runoff is produced, whether the saturation of the soil profile starts from the surface or is a result of a rising ground water table. So that's the first aspect of land use change.
Then, the second other factor that may change floods or flood hazard are hydraulic structures, river regulation, river training, and here the situation really depends on the local conditions. River training, of course, has a high potential of increasing floods because of the loss of floodplains. So as levees are constructed along the rivers, the river is constrained to its main bed. And the attenuation of the flood wave by storing water in the floodplains is lost, which can increase the magnitude of the floods. But this again, does not relate to the largest of the largest floods, because the largest floods overtop the levees anyway. These effects are for intermediate and moderate floods. So this is hydraulic structures.
And then the third factor, the third process affecting floods, is of course climate change, as mentioned previously for the 500-year study.
We did a similar study and analysis of climate change effects on floods for the last 60 years in Europe, based on the thousands and thousands of stream flow observations in a big project funded by the European Research Council. In this project, we found that they're very clear patterns of flood changes in Europe. Based on observations, not based on modeling. We see that in northwestern Europe, floods are increasing whichh has to do with more frequent and intense storms related to shifts in the storm tracks. So, generally speaking, northwestern Europe is becoming wetter, soil moisture is higher. Rainstorms tend to increase and that's why there's a quite a clear tendency of increasing floods.
Then in Eastern Europe, we see a trend of decreasing floods very clearly, very strong decreases. This has to do with a completely different process in this region of the world. Floods are mainly snowmelt floods. Because of warmer temperatures, snowpacks are shallower, so snowmelt is less, and therefore the potential of flooding goes down. We also see a shift of processes: fewer snowmelt floods and more rain floods.
On the other hand, in Southern Europe, in the Mediterranean, we see two effects.
In medium sized and large catchments floods actually go down, they decrease, and this has to do with the increased evaporation. Evaporation is changing big time in Europe with the warmer temperatures. For example, in Austria, evaporation in the past 40 years has increased by 17%! Again, based on measurements, not based on modeling. What I tell my students is that the amount of water that Austria loses because of the extra evaporation is equivalent to the entire drinking water consumption of the world. That's a huge amount of water that's lost to the atmosphere because of the enhanced evaporation. And one of the effects of that is that soil moisture is lower, which reduces the flooding. In southern Europe for medium sized and large catchments.
The second effect applies to flash floods. That is floods that are produced by thunderstorms, short duration, small spatial extent, and you have convective processes. We see increases in these convective events. The interpretation is because of more energy in the atmosphere, there's more potential for these very intensive storms. And we see the fingerprint of these enhanced thunderstorms also in flood damages, in particular in small catchments and in the south of Europe, also enhancement of landslides that are triggered by these very intense, short duration storms.
[00:21:12] Bridget Scanlon: Well, I mean, it's really important to understand these processes and the flood generation mechanisms, but oftentimes we simply just say heavy rainfall flooding, ergo flooding, but it's much more complicated than that. And I think your recent paper in Communications, Earth and the Environment that review in 2023, you talk about the shifts in the flood generation processes exacerbate European flooding rather than the changes in extreme rainfall. That was a very nice analysis looking at rain, dry rain, wet rain, snow and snow melt and increases and decreases in flood frequency. And I think that's some of what you were referring to in just the previous response.
[00:21:57] Günter Blöschl: Yes. So there's shifts in the flood mechanisms, for example, in Eastern Europe, more rain floods, fewer snow floods; in Southern Europe shift towards more flash floods. The mechanisms matter because the change in flooding differs depending on what type of flood we are looking at.
[00:22:25] Bridget Scanlon: And I really like that you emphasize the impacts on different catchment sizes and different flood sizes. Not that one size fits all. These generation mechanisms vary with the size of the catchment and the type of flood.
So it's very important to distinguish that those things, small local floods, convective storms that climate change may be impacting, but then larger floods, larger catchments, more storage impacted. And so this understanding is critical if we're going to develop solutions for flooding issues. I think your 2017 Science paper was very nice in looking at climate change impacts on the timing of floods using that 50 year record of data from 1960 to 2010.
Maybe you can describe that a little bit with the temperature increases and the changing in timing of flooding.
[00:23:19] Günter Blöschl: Yes, the timing of flooding is an interesting concept. The idea is the following. We look at the largest discharge in any one year and note the date or the day of that peak discharge within the year, and we do this for every year.
And then we calculate the average date over all of these years of the series of flood occurrences. And what we see when we plot the map, quite interesting map for Europe, for example, we see the regions where we have winter flooding, such as the British Islands or the Mediterranean, we can see regions of summer flooding, Central Europe, and then regions of spring flooding in Eastern Europe because of snowmelt, and this timing index gives us a first insight of the causes of the floods, that is, the processes that drive the floods, such as snowmelt, short intensive rainstorm, long duration rainstorms, rain on snow and so forth.
And then we looked at how this timing indicator, how this has changed over the last decades. This change gives us a fingerprint of climate change effects on flooding that is directly read from the data, just very direct data analysis with no modeling, no predictions, but we just look at the data through the lens of this process indicator. We see that in the northwestern parts of Europe indeed the floods are changing because of higher rainfall which translates into earlier floods. So on the British Islands, floods are occurring now a couple of weeks earlier than they used to a few decades ago, and also earlier floods in Eastern Europe because snow melt occurs earlier because of warmer temperatures.
We also see shifts in flood timing in Southern Europe that have to do with the enhanced evaporation. So it's a different way of looking at the flood problem, not just at the flood discharges and associated probabilities, but a different indicator to shed more light on the generating processes of the floods, because these are very important if you want to predict future climate driven floods, changes driven by climate or other mechanisms, such as land use change and hydraulic structures. Without this process understanding we are really groping in the dark, we need to see what are the reasons for these floods, which then allows us to predict the reasons for the flood changes and then the magnitude of the flood changes.
[00:26:10] Bridget Scanlon: Well, I really appreciate your data driven approach, and I think it's a necessary first step before we can go forward with the modeling and other things, and so it's really nice that you put a lot of emphasis on analyzing the data and long term historical records to look at trends and put the current situation in the context of the long term.
So, I know it's a career to collect all these data and to analyze it, but... But it's really nice at the end to be able to document, and as you say, fingerprint and the timing helps you understand the processes. So, so that's great. So this improved understanding of flood generation mechanisms and the variations across catchment size and flood size and stuff, that helps us then, I guess, develop appropriate solutions to managing floods, and traditionally we've relied heavily on engineering approaches, then more recently it seems like there's a lot of emphasis on nature based solutions like wetlands and other things. But I think your work emphasizes that we need all of the above and a portfolio of solutions to address flooding issues.
Maybe you can describe some of that and what is appropriate for different size floods or different catchments or some of those aspects.
[00:27:35] Günter Blöschl:. Yes, one could say there are horses for courses to use a horse racing expression. Depending on the local situation, some of the solutions may be more efficient than others.
For example, starting with engineering solutions. If we talk about flood risk management in small catchments, that is for small creeks with small catchment areas, building a retention basin to hold the floodwaters back is often a very efficient solution because the volume of the flood waves are small, so it's easier for a given reservoir size to take up a large chunk of the flood waters.
As we go up in scale to large rivers, the flood volumes become immense. For example, for the Danube flood in 2013, the volume of the flood hydrograph was four billion cubic meters of water. And in other river basins, the flood volumes are even bigger.
We're talking about billions of cubic meters of water. It is still possible to build retention basins, but for a given basin capacity, the reduction in the water levels that are possible become very small for simple mass balance reasons, and then these structures are no longer cost effective.
Even for large catchments, building retention areas or basins is still a good thing, but we need to be aware that the actual flood reductions that can be achieved become smaller and smaller.
And this is the main reason that levees are built as an alternative, because they do not depend on the flood volume. Their efficiency only depends on the water level, but not on how long the flood wave takes. While the retention basins have to do with the timescale of the flood hydrograph, the levees are not related to the timescale. They are equally efficient for short and long floods.
So this is the basic difference between retention basins and levees. But then of course, there's a multitude of other possibilities, both structural and non structural solutions, insurances, evacuation, and flood warnings.
There are also, as you mentioned, green solutions. And these green solutions, they have become very popular in the last years, in particular in Europe, where we have now the policy of the Green Deal, trillions of Euro go into a green and carbon free economy.
In Europe green management solutions of floods are part of the overall Green Deal. So what could be a green solution, a green infrastructure for the case of flood management? There are a couple of them. Of course, one could be afforestation, so planting trees, but as I have already said, this is not an efficient measure for reducing big floods.
An alternative are wetlands. Wetlands have the extra advantage that they're also very good for other reasons, for ecological reasons, for biodiversity, and there's no doubt about that. The problem with wetlands is that their effectiveness depends on the amount of water they can store during the flood, and the amount of water is usually very small.
So the way of assessing the efficiency of these kinds of measures in the first instance is: what's the volume of water that can be retained relative to the volume of the flood wave? And then if we say, okay, the Danube flood has a volume of 4 billion cubic meters of water, a wetland can retain 4 million cubic meters of water, then we see immediately this wetland has no effect whatsoever on the water level.
So again, wetlands can be very useful for other purposes, but for flood retention, they are usually not so useful. They may make a contribution to other solutions, but are rarely a solution by themselves.
Another possibility of green infrastructure would be micro ponds. These are small retention basins in the landscape where water can infiltrate. These solutions can help, but we need to look at the total volume of water they can actually store. And there are also issues with sedimentation that can result in siltation of these ponds. They can fill with sediments, and then it may be expensive to maintain them. So, yes, there is green infrastructure, but green infrastructure is certainly not the silver bullet for solving all the flood management problems. They can contribute. But other more traditional flood management measures, including infrastructure, engineering measures, structural measures, financial measures and emergency measures, they still will play a very important role in the future.
[00:33:17] Bridget Scanlon: Right. So it's really important to consider the volumetrics apparently, and sometimes we lose sight of that. You mentioned 4 billion cubic meters of water flooding in the Danube. And so that's equivalent to 4 cubic kilometers. And for the American listeners, that's approximately 4 million acre feet to translate to units that they may be more familiar with, but that's a lot of water.
And so trying to retain that. Then you mentioned retention ponds and I presume, you are including reservoirs when you dams and reservoirs. When you mentioned the retention ponds, that's another aspect, that you are considering and the micro ponds, I know when Australia was going through the millennium drought and they had rainfall events and they were wondering why they weren't seeing the impact of those rainfall events in the reservoirs downstream. And some of them were saying, well, maybe it's all these, small farm ponds or micro ponds that is collecting. So during a drought, that may not be the best thing to have, So it's a very difficult to consider managing these various extremes.
[00:34:28] Günter Blöschl: Yes. Yes. For each of these measures there are pros and cons. So as I said, for microponds, sediments can be a big issue. In the drought case, microponds have the disadvantage that evaporation is huge relative to the water volume stored because they are shallow. So tens of thousands of microponds may have a regional effect on water availability because of the water loss from extra evaporation.
[00:34:59] Bridget Scanlon: Right, right. And I think more and more, we're not just dealing with floods, we're dealing with droughts and floods, as we mentioned earlier, so trying to manage these extremes for water management is a difficult issue, challenging, very challenging.
[00:35:15] Günter Blöschl: We actually conducted a recent study in South America together with colleagues from Florianopolis. We have looked at the joint occurrence of flood changes and low flow changes because generally it is said, well: floods are increasing everywhere. Droughts are increasing everywhere. While the reality is, as I said before, floods are increasing not everywhere.
If we look at the global map of flood changes based on observations, we will see that in about two thirds of the catchments, so 60% of the catchments worldwide, floods are increasing, and in the rest, floods are decreasing. So there is a tendency for more catchments with increasing floods, but certainly not 100%.
And the same applies with droughts. There's a tendency for more droughts to occur, but this is certainly not the case everywhere. Some parts of the world are wetting up and the number of droughts is decreasing. And South America is an interesting case where we looked at trends in both floods and low flows.
It's a joint analysis of two things. In one third, 30%, 40% of South America, we see increasing floods and decreasing low flows, which means stronger droughts, suggesting that the regional water cycle is accelerating. But in other parts of South America, both low flows and flood flows are increasing, and everything is getting wetter. In still other parts, for example on the East Coast, which is an agriculturally heavily used area with lots of water withdrawals for irrigation purposes, both floods and low flows are going down. Everything is getting drier. So it is not necessarily the case that both floods and droughts get worse. There are also other cases, very relevant cases, where this is not so.
[00:37:20] Bridget Scanlon: Well, I think it's extremely valuable that you actually look at the data. That's so important. We had Esteban Jobbagy on the podcast earlier, and he was talking about flooding increasing in Argentina because of expansion of agriculture, water table, groundwater tables rising and resulting in floods driven by shallow water tables and stuff.
So that was very interesting. So you've looked at a lot of aspects of flooding and I know you've done a lot of detailed work in Austria. I found one paper, but I think it was written in German, which I couldn't, I could read the abstract, but not any further, where you talk about flood risk management in Austria. And I think I have heard of HORA or is that maybe you can describe that a little bit, what you are doing in Austria to deal with these things.
[00:38:14] Günter Blöschl: Yes, the study you are referring to is a project I concluded a couple of months ago for the Austrian Ministry of Agriculture and Water Management.In this project, we conducted a flood hazard mapping for the entire country. This was quite an interesting study from a hydrological perspective because we did a hydrological flood frequency analysis for the entire country. Like a spatially consistent analysis of all the flood observations we had for estimating five hundred year floods for the entire nation.
And that was used as an input into hydrodynamic modeling. You could say hyper resolution modeling for the entire country, where we, together with partners from industry, we applied hydrodynamic models, non-stationary models, with a spatial resolution of two meters. For a country of almost 100,000 square kilometers, you can imagine lots of cells, a time resolution of a couple of seconds, and then we simulated flooding scenarios from which we derived dynamic flood hazard zones. These zones are used for risk management. They're used for the insurance industry, but also for decisions regarding urban developments. And there are also used by the general public.
It's interesting to say that the flood hazard, the flood risk, is a key thing for many ways of managing floods or improving the living conditions of people. But it's also relevant to take a broader view of going beyond a scenario of say, a 100 year flood and its effect on inundation levels, the extent, and the water depth, and the flow velocity, which these models give us. The broader view, I think, will become even more important in the future. Looking at it from a broader perspective, from the perspective of the interactions between society and water. And this is the argument which gets us into sociohydrology.
[00:40:40] Bridget Scanlon: Oh yeah, I was definitely thinking of that, the social hydrologic aspects, the linkage between human behavior and the flooding and engineering aspects.
I mean, talk about the levee effect, you build a levee, people think it's more secure then they start to build. Maybe you can describe that a little bit.
[00:41:01] Günter Blöschl: Sociohydrology is the discipline that deals with the dynamic interactions between people and water. So it goes beyond what we've been doing traditionally, just looking at scenarios where we have like an increase in rainfall of 10%, we run this rainfall increase through a runoff model, and then look at its effect on society. Or we look at the effect of society on water quality.
In contrast, in sociohydrology, we look at the two way coupling of people and water. Two way coupling means that water affects people, and people affect the water. The hydrological cycle may change which, in the long term, motivates people to do something to change the hydrological cycle again.
So it's a coupling. You mentioned the levee effect and that's quite interesting and not at all intuitive what's happening there. If levees are built along the river to protect the flood plain, a natural response of the local community is to move into this flood plain, because the construction of the levee conveys to the population a sense of security.
People feel secure. The value of the land goes up, the area is developed. And then the counterintuitive effect is that, even though the levee is built in order to reduce the flood risk because the probability of an inundation goes down, the increased assets on the flood plain because of the development increases. A smaller probability of flooding, but a much bigger value of assets that is at stake.
And then as a consequence of the bigger value of assets due to the construction of the levees, the flood risk goes up in the long term. This is an unintended consequence. This is a consequence the engineers who do the design usually are not aware of. I believe strongly that we need to shift our thinking to go beyond one individual engineering measure and to look at the longer-term perspective, in interdisciplinary collaboration with the social sciences. Different disciplines need to look at this coupling and the potential consequences of the engineering measures.
The levee effect is only one of many examples where we can see this coupling in water management, where the traditional scenario approach is no longer valid because the scenario approach does not look at the coupling. We need to look at the dynamic effects of the coupling for floods, but the same applies for droughts. We have very similar effects in the interaction between droughts and people. For example, an effect that's known as the rebound effect, meaning that if you increase the efficiency of irrigation, you hope to save water because you need less water for growing an amount of crop, but then in reality, what's happening often is that the more efficient irrigation increases water consumption, because it conveys a sense of water availability. So farmers will use more land or plant crops that use more water, and as a result, you thought you were saving water, but as an unintended consequence, actually water consumption goes up because of these feedbacks.
I think we need to consider these very carefully in the future for strategic development of long-term water development measures.
[00:44:56] Bridget Scanlon: Right. And I totally agree with you. And we had an earlier person, Quentin Grafton in Australia, talking about the Murray Darling Basin Plan and a lot of emphasis, 7 billion on precision agriculture, and not only maybe they expanded the irrigated area and the rebound effect, but they also didn't take into account that they were losing the inefficient recharge they were getting of the aquifers from inefficient surface water irrigation. And so it's really important, and I think we are recognizing where we need to work more with social scientists.
These are not just technical problems, physical data requirements. We need to understand human behavior and the impacts of different aspects in the hydrologic cycle. So I really appreciate the work that you and your colleagues have been doing in social hydrology and bring highlighting those interconnections.
So with all of your work on flooding aspects and trying to understand the causes and optimal solutions and providing deep insights and the data driven approach, and the long term records, it's really fantastic. How do you see the future? Are you, do you think positively about the future that we will be able to adapt and manage these things and learn from these experiences and improve the situation or what are your thoughts?
[00:46:21] Günter Blöschl: This question is not a technical question. It's more a philosophical question. And personally, I'm very positive. So I think positive about the future. To use a simple example: the glass is half full, not half empty, the way I look at it. Of course, the future will not be easy, but also the past has not been easy for humankind.
In the past, people have managed to come to grips with their new challenges. And each century has had, has had heaps of new challenges, social challenges, technical challenges, environmental challenges, political challenges. And I'm confident that humankind will also very much be able to come to grips with the future challenges, economic, environmental, but also very much social.
And one of them is, for example, equity. We have not talked too much about equity in flood management, but this is to my mind, a very important issue because there's a systemic tendency for the weaker parts of society to lose out, and I think we really need to have this on the radar.
That equity is a very important goal to achieve in water management, in flood management, in drought management. There are many examples where this goal of equity is achieved to a larger or to a lesser degree. So equity, I think, should be high on the priority list if we think about future water management policies.
Right.
[00:48:08] Bridget Scanlon: I think, the U. S. is grappling with that right now and the overlay social vulnerability on flood mapping and flood exposure and stuff. And they have a 50 billion infrastructure funding for water. And so some of that will go to try to address some of those aspects. Well, I really appreciate your time today, Günter, and thoroughly enjoyed reading your papers and trying to understand there was so much to absorb, and I think you have synthesized some of the key aspects very well today. So, thank you so much for your time, and looking forward to talking to you again in the future.
[00:48:43] Günter Blöschl: Thank you, Bridget, for the interview. Thank you so much. Bye bye.
