’We have to make the urban water cycle close to nature again’

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For modelling future groundwater levels, Daniela Fuchs-Hanusch would like to see
For modelling future groundwater levels, Daniela Fuchs-Hanusch would like to see detailed data on water consumption, especially in agriculture. At present, researchers still have to rely on estimates. Image source: Lunghammer - TU Graz

By Philipp Jarke und Falko Schoklitsch

How can we deal with droughts and floods? To what extent are we ourselves to blame? An interview with Daniela Fuchs-Hanusch from the Institute of Urban Water Management and Landscape Water Engineering at TU Graz.

News + Stories: We seem to move back and forth between extreme states: either we have far too much water or far too little. Are we ourselves to blame for this situation?

Daniela Fuchs-Hanusch: By intervening in the water cycle, we become jointly responsible. Take the heat island effect in cities - rising heat increases the intensity of thunderstorms and the intensity of precipitation. Or surface sealing - much of the urban precipitation flows relatively quickly into the sewage system; in heavy rain too fast. The sewage system cannot be dimensioned to such extreme events, and this is not even a requirement of the design standards. A residual risk is therefore always to be expected. So we are also influencing the type and intensity of heavy rainfall events, and particularly their impact. And sealing also reduces groundwater recharge, at least regionally.

That means, sealing and a lack of green space are factors that create so much heat in cities?

Fuchs-Hanusch: Exactly, heat islands in cities are the result of sealing. Recent studies also show that parked cars still emit a lot of heat at night, therefore the necessary cooling does not take place. We don’t even need to talk about the traffic itself.

Does the type of materials used in buildings and roads also play a role in heat accumulation?

Fuchs-Hanusch: The design of surfaces certainly plays a role, whether the colour, the material or the structure. Surfaces that absorb precipitation, release it through evaporation and thus cool the environment are ideal. Therefore, green urban areas are enormously important. Their evaporation capacity stabilises the local water balance and reduces the heat island effect. However, many cities are now planting drought-resistant trees. The problem with this is that their evaporation and cooling effect are very low. To sum up, keeping water in the city and making the urban water cycle more natural again is crucial.

Is there a necessary awareness of the water cycle in urban planning and architecture?

Fuchs-Hanusch: It could be bigger. With the UniNEtZ project, which among other things deals with sustainable neighbourhood development, we were in the Sonnwendviertel, Vienna’s showcase neighbourhood. I was shocked to discover that the natural urban water cycle hardly plays a role at all. Although the neighbourhood has a large park, it is otherwise heavily sealed, only very small trees have been planted, there are no green facades and no biotopes, although there would be enough space.

What conflicts of interest lead to water hardly being taken into account?

Fuchs-Hanusch: We are looking into this right now. A co-initiator of a building group in the Sonnwendviertel told me that there is affordable housing, traffic calming, rental and cargo bikes for everyone, and small shops - but not everything is possible. At least there is a showcase project with green roofs, photovoltaics and a small garden on the roof. But concepts of the sponge city - e.g. the storage of precipitation water in the extensive untravelled areas - were not taken into account. In existing parts of the city this is difficult anyway, but in the development of new neighbourhoods it is a real pity if this is not implemented as well.

Buildings can be designed in such a way that they do not disturb the natural water balance.

Is there also a connection between housing type and water consumption?

Fuchs-Hanusch: Yes, there is. We are currently working together with BOKU (University of Natural Resources and Life Sciences, Vienna) and the Ministry of Agriculture on a study on water demand and consumption peaks depending on the type of housing. The single-family detached house with a pool is, of course, at the top, both in terms of average consumption and the peaks that occur when the pool is filled. Water consumption is lower in appartments. It does make a difference whether people realise their dream of a single-family home or whether urban space is densified and buildings are equipped with green roofs and fašades and public recreational space, including water areas, is made available to people. Buildings can also be designed in such a way that they do not disturb the natural water balance.

What is your research focus at the moment?

Fuchs-Hanusch: My current focus is, among other things, on sustainable neighbourhood development, and here of course on the topic of near-natural urban water balance. This is a big challenge for me as an engineer. The groups I am active in are transdisciplinary, with sometimes very different approaches to the topic. A colleague from architecture is trying to develop sustainability indicators, others from sociology are analysing at meta-levels. I find such a diverse team very enriching.

What would be a water-related measure to make urban neighbourhoods more sustainable?

Fuchs-Hanusch: The use of grey water, i.e. previously used water from households - excluding black water (toilet waste water). Grey water use is not exactly popular in Austria. People always say that two water circuits are too expensive. Moreover, water must currently be of drinking quality in the entire household, even in the toilet - after all someone might get the idea to drink from it. In my opinion, we should definitely think about using grey water when greening facades in cities. This works very well. For example, one of my PhD students used machine learning methods to investigate the irrigation needs of a green wall. According to initial estimates, the amount of grey water from dwellings is sufficient to cover the calculated irrigation needs of the plants, depending on household sizes and housing types.

Watering green facades with rainwater is difficult due to the irregularity of precipitation and the storage volumes required as a result. Grey water can also be made usable in existing buildings in the course of renovation work on the plumbing; this would mean that drinking water could be dispensed with as irrigation water. Of course, these concepts must take into account the energy required to recycle the grey water and the amount of water required for the functioning of existing alluvial sewers.

How has drinking water consumption in Austria developed in recent decades?

Fuchs-Hanusch: Average per capita consumption in Austria fell from the 1970s to the end of the 1990s because a lot was invested in efficient appliances. There are therefore hardly any more savings to be made in household water consumption. But with the increasing heat and the long dry periods, water consumption and especially irrigation consumption in households with gardens is rising. Here, too, it is worth considering the use of grey water.

Water supply companies often don’t like it when people call for saving drinking water...

Fuchs-Hanusch: That’s right, because the high fixed costs for the pipeline network and technical infrastructure are largely financed through consumption fees, and the fixed costs do not change when people use less water. When I wrote my doctoral thesis, the utilities’ message was that saving water is quite counterproductive. These voices have now become quieter because falling groundwater levels can be observed - especially in the east of Austria. Some utilities want to develop new water resources. For sustainability reasons, I ask myself what urban development, changed forms of housing and alternative ways of dealing with water can contribute to ensuring that we do not have to tap additional resources?

This article is part of the current TU Graz dossier " Flooded and dried out " on the topic of electromobility. At www.tugraz.at/go/dossiers you will regularly find news, interviews, basic information, contacts to experts, videos, podcasts and expert opinions on a new focus topic.

What are the causes of the increasingly frequent floods, apart from climate change and the soil sealing you describe? Is it also due to incorrect soil management in agriculture?

Fuchs-Hanusch: Some types of cultivation and crops are indeed runoff-promoting, maize for example. That is why the hype surrounding biogas has quickly fallen into disrepute. Not only does maize cultivation require a lot of fertilisers, some of which end up in groundwater and streams, it also promotes run-off and soil loss, one of our biggest problems worldwide. As far as passive flood protection is concerned, forest is an important factor. A natural forest has very little surface run-off. A colleague of mine therefore says: "The water cycle of a city should be brought back to that of a forest again." There are architects who deal with this, but it is not technically that easy.

Are there engineering options to reduce flooding?

Fuchs-Hanusch: They definitely exist, flood retention basins and the like. But that’s not really my thing. If I plan underground storage, it must be large enough for extreme events. But there are limits. My message is something else: restore the urban water cycle to its natural state. Heat island reduction through urban greening with sponge-city concept where possible. Technically, however, there are still challenges. Urban greenery needs relatively loose substrate, which is unfavourable for streets with heavy traffic. So the space for sponge city elements is limited to areas such as pavements and cycle paths. We also have to ask how we are going to irrigate urban green areas. This is a huge issue. Do we plant a lot of trees, all of which are irrigated with drinking water?

Your approach would be to use grey water for this?

Fuchs-Hanusch: For the fašade, definitely. A BOKU project took a look at this. The grey water was completely unpurified, but the plants tolerated it well. There was even a cleansing effect.

Such innovative concepts should not be completely thwarted by strict guidelines.

As a layman, one would think that grey water contains a number of pollutants. Is this a problem?

Fuchs-Hanusch: We have a lot of research to do in this context. This particularly affects the sponge city concepts, since here surface pollution comes from the street. Investigations into this are underway. I personally think that such innovative concepts should not be completely thwarted by strict guidelines. We should at least look at what degree of cleaning is possible in the area of tree roots and substrates and what additional technical measures are necessary. Critics say it is all very high-maintenance and expensive. But what are the long-term and economic costs if we do nothing about heat in cities? Many talk about climate change adaptation. I can’t hear this any more. I don’t want my research to be just about adaptation any more, nor always being one step behind. For me, it is time for a step forward, in other words to do something about the climate crisis in a regional context.

We mentioned the low groundwater levels earlier - to what extent is our use partly to blame here?

Fuchs-Hanusch: It’s quite clear worldwide that the low groundwater levels are the result of massive overexploitation. Parts of Spain and the USA can no longer use groundwater, there simply isn’t any left. It will not come to that in our country, because in most of Austria we have a very positive climatic water balance (precipitation vs. evaporation) and thus enough groundwater recharge takes place. In eastern Austria, on the other hand, the climatic water balance is already negative. In southern and south-eastern Styria we have had a change in the climatic water balance towards a deficit in the last 20 years. In this context, greater monitoring of all uses, especially agriculture and industry, should also be considered in the near future.

Climate change is an important factor, but are we also extracting too much groundwater?

Fuchs-Hanusch: We can’t say for sure at the moment. There is the Austrian Water Resources Study of the BML (Ministry of Agriculture, Forestry, Regions and Water Management), which does not show that we have overuse. The estimated share of agriculture in Austria is surprisingly low. Unfortunately, we do not know the exact groundwater use because it is not measured except in the drinking water supply. It is currently not state of the art and also not legally required to measure the use and report it to any authority. This is only done for the water supply companies in order to calculate balances from production and consumption, to be able to recognise water losses or to be able to determine the daily water consumption.

So farmers can set up their sprinklers as they please?

Fuchs-Hanusch: They have to apply for a permit under water law. The notices issued usually state how much they can withdraw each day and usually have very long terms. The groundwater is then extracted as needed; in drought years more than in wet years. Surveys have been done, but it is not known exactly how much water is actually used. Industrial use in Austria is the largest factor, accounting for 70 per cent of water consumption. Four per cent is for agriculture, the rest for drinking water supply. The share for agriculture will increase, but it is an important question how this can really continue. We need groundwater modelling with simulations of a wide range of use scenarios.

But this would require real, reliable usage data to first determine the status quo.

Fuchs-Hanusch: Absolutely. That would really be necessary so that we can set up groundwater models and find out how strongly the groundwater is already influenced by uses. That also appeals to me from a scientific point of view. In a conversation with representatives of the Ministry of Agriculture, I was able to learn that there is also a desire to increasingly measure water consumption in agriculture. But it’s not just the high-resolution data in agriculture that is missing. Even in the cities we’re lacking really good data up to a point, especially smart meters - meters which allow us to at least measure daily use. Unfortunately, smart meters are still rarely used in drinking water supply in Austria. For the sector, the advantage of smart meters is still not apparent.

So it’s not the consumers who are against smart meters because they don’t want to be transparent?

Fuchs-Hanusch: There will always be a few. But I would say that the water supply companies themselves are putting the brakes on. In the electricity sector, it is mandatory to at least offer smart meters. It would be desirable if this also existed in the water supply.

I hope that digitalisation will arrive in the world of water.

Would a more precise data basis help to organise cities in a more water-saving way?

Fuchs-Hanusch: Yes, definitely. If we had this data, we could analyse much better in what kinds of housing consumption is increasing very strongly in the context of climate change and in what kinds it is not. In the context of water efficiency, this is essential. Of course, it would also go a long way towards ensuring that water supply utilities themselves consume as little water as possible, for example in the form of leaks and losses.

Are there possibilities to artificially replenish groundwater? For instance, by feeding in surpluses during periods of high rainfall, or on a small scale during heavy rainfall events and floods? Or is that unrealistic?

Fuchs-Hanusch: That is not at all unrealistic. In urban areas, if you try to hold water through temporary storage - but not in concrete basins - it will also be added to the groundwater. This also plays a role in passive flood protection, e.g. in forest management. In Bavaria, people are trying to retain water in the forest by digging small pits and leaving trees on the ground. This benefits the trees, but also helps water to percolate locally. In the city, we should consider the use of intensive green roofs. Roofs that have a higher structure, where water is held and where even trees can grow. Then there is no heavy run-off at all. All these small measures in near-natural rainwater management promote local storage and slow down and reduce run-off.

And by the way, the artificial recharging of groundwater that you mentioned has been going on for a long time, in Graz for example in Andritz and in Friesach. There, however, retention serves to change the flow direction of the groundwater. The intention was to protect the drinking water wells from the very dirty water of the Mur of the time. In other regions of the world, surpluses from rainy periods are actually added to the groundwater in order to be able to use the water in later dry periods. In India, for example, there are many small dams that hold rainwater during the monsoon and allow it to seep away locally so that it can be used later for irrigation.

Regarding the topic of water: what would you like to see in the coming years?

Fuchs-Hanusch: I hope that digitalisation will arrive in the world of water and that measurement data will increase. I would like to see continuous time series with data on water demand and use so that we can build accurate models for dealing with the climate crisis and work through different scenarios. In this way, alternatives in urban development or irrigated agriculture could be compared with each other. We have excellent climate models, including regional ones, but we do not have the necessary baseline data to calibrate our water demand models. For this purpose, a time series of water consumption over the last 20 to 30 years would be ideal. We could link these data to regional climate data and thus calibrate the models of the hydrological cycle. So, more measurements!

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