OF WATER

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plus

WORLD

OF WATER

Germany’s researchers join forces

in Water Science Alliance

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Cover photo: J. Lösel for bdw

Water – surely not much of a problem in our little corner of the planet? After all, we can get as much clean water as we want straight out of the tap whenever we need it, so it can hardly be ranked as a scarce resource. Or can it? Delve a little deeper and all sorts of challenges start to become apparent. For example, torrential rain is becoming more frequent, and that means we’re seeing more overfl owing rivers and fl ash fl oods. At the same time, water experts are warning of an increase in average annual temperatures in areas such as the Mediter- ranean and changes in the distribution of precipitation across Europe.

And heavily populated regions are facing an additional problem: Their waste water is teeming with strains of bacteria that are resistant to antibiotics and that pose a risk to their drinking water supplies.

From a global perspective, our water problems have taken on even more worrying dimensions. Water use has quintupled over the past 50 years and this trend looks set to become even more dramatic as the global population continues to grow and living standards continue to improve. Many people are already predicting that the wars of the 21st century will be fought over water.

It is estimated that there are some 450 water science departments in approximately 150 research institutions in Germany alone, all of which are working on issues relating to water. That’s good to know – and yet it’s far from being good enough. The fact is that hydrological research in Germany is more of an old-fashioned patchwork of petty statelets than a dynamic, modern alliance. “Germany is not the only country recognizing that this can’t continue,” says Bill Cosgrove, Director of the World Water Scenarios Project, in an interview that begins on page 30 of this special “World of Water” issue of bild der wissenschaft.

Germany’s potential in the fi eld of hydrology is currently hard to discern on an international level. Improving its visibility is one of the aims of the new Water Science Alliance, which was established in 2009 by the Helmholtz Association, Germany’s largest scientifi c organization. The stated goal of this initiative is to facilitate communication and knowledge exchange between the various members of Germany’s water research community in key thematic clusters. This approach is long overdue, and many of the issues involved are highly sensitive.

I hope that you gain plenty of fascinating insights into water – the elixir of life – in this special issue of bdw. I know I did!

Forging a uniﬁ ed alliance from a patchwork mix of experts

“World of Water”:

A journey through the most compelling issues in water research today Wolfgang Hess,

editor-in-chief

wolfgang.hess@konradin.de

COMMENTARY CONTENTS CONTENTS CONTENTS

4 Extreme floods

Heavy rainfall is becoming more frequent worldwide – but why?

12 Future scenarios

Forecasting precipitation in Germany is a tricky task

18 What is water worth?

Factoring in the environmental costs 22 Everyone wants their share The era of water conflicts 25 A measured approach

The challenge of comprehensively mapping soil moisture

26 An unexpected surprise

It may seem harmless in the lab – but it could still damage the environment 29 Creeping threat

To what extent does groundwater clean itself?

30 Join in!

Interview with water expert and top manager Bill Cosgrove 34 In the urban jungle

What’s lurking in the sewers?

36 Editorial notes 37 A good start

Georg Teutsch discusses the Water Science Alliance initiative

38 Treasures of the deep

Researchers look for ways of tackling water shortages in Mediterranean countries 44 Water research in Germany

Facts and figures

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W. Scheible

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EXTREME

FLOODS

Far too much of a good thing: Torrential downpours are getting more frequent, say weather and climate researchers – and that makes more riverine and fl ash fl oods inevitable. So why is it happening? And what – if anything – can we do about it?

picture-alliance/AP/Calanni

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W E AT H E R A N D C L I M AT E

On November 4, 2011, raging floods washed hundreds of cars through the streets of Genoa.

The amount of rain that fell on the mountainous Ligurian coast on that one day was equivalent to the total precipitation that falls in some parts of Germany over the course of an entire year.

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W E AT H E R A N D C L I M AT E

Devastating debut on November 3, 2011: Tropical storms are a regular occurrence in the Caribbean, but the extratropical low “Rolf” was the first cyclone to hit the Mediterranean region. The spiral-shaped storm hit the Ligurian coast (at top of picture, North Africa at bottom) bringing torrential rain and winds of more than 120 km/h.

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THE TROPICAL STORMS that hit the Phil- ippines each year normally affect the north – but on December 14, 2011, Trop- ical Storm Washi took everyone by surprise when it slammed into the Philip- pine island of Mindanao in the far south of the country. The worst part was not the strong winds, but rather the torrential rain. Meteorologists recorded up to 239 millimeters of rainfall in just 24 hours, resulting in fl ash fl oods, mudslides and landslips. The water cut deep scars into the landscape and washed away everything in its path, including trees, houses and heavy vehicles. The island’s inhabitants were caught in their sleep, and more than 1,000 of them perished.

At around the same time, some 2,500 kilometers to the west, other areas were also under water. Unusually intense monsoon rains compounded by multiple tropical storms had caused rivers in Thailand to burst their banks. The capital Bangkok was hit by fl ooding that lasted several weeks, causing damage across the country estimated at over ten billion euros.

There was no escape for Europe, either:

Extraordinary images from Genoa in the fi rst week of November 2011 showed raging water washing cars through the streets like matchsticks. On that one day up to 465 millimeters of rain fell in Liguria – roughly equivalent to the amount of rain that typically falls in the German region of Magdeburg over an entire year. The disaster was caused by an area of low pressure nicknamed “Rolf” which many meteorologists classifi ed as a tropical system because of its spiral shape – even though tropical cyclones of this kind should simply not occur in temperate Europe.

Are these the fi rst effects of climate change? Can we expect to see increasingly severe weather-related disasters in the future? According to the reinsurer Munich Re, fl ood events have almost tri- pled around the world since 1980, while

BY KLAUS JACOB

EXTREME

FLOODS

damage from fl ooding has rocketed by a factor of fi ve. Yet care must be taken in interpreting these fi gures. Taken in isola- tion, they do not provide proof of climate change or its consequences because they can primarily be attributed to changing population distribution. The number of people on Earth has now risen to more than 7 billion. Generally speaking, people prefer to live close to water and are not afraid to settle on fl oodplains. In ad- dition, people are accumulating more valuable possessions, ranging from a freez- er in the cellar to robots in production facilities, and the damage water infl icts on the electronics contained in virtually all machines pushes the losses involved in weather disasters even higher.

In short, society has become more fragile, exhibiting what experts refer to as “increased vulnerability”. And of course human beings are affecting more than just the climate. We are covering ever larger areas with streets and houses while clearing forests and leaving hill- sides to erode. The result is that rainwater is no longer retained by the vegetation and soil, but instead fl ows straight into streams and rivers.

REDISTRIBUTION OF PRECIPITATION These factors aside, it also seems likely that climate change is playing its own part in this worrying course of events.

Yet scientists are struggling to draw clear conclusions, even when it comes to precipitation: “What we are witnessing is more of a redistribution than a global rise,” says Andreas Becker, who heads up the Global Precipitation Climatology Center (GPCC) which is operated by the German Meteorological Service DWD.

Precipitation is increasing in northern Europe, especially in winter. At the same time it is decreasing in southern regions along the Mediterranean coast. Mexico and West Africa are also getting drier,

NASA

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W E AT H E R A N D C L I M AT E

while Northern Australia is getting wetter.

The complexity of the situaton is evi- dent even in Germany, which appears as a patchwork of zones of increasing and decreasing precipitation. Generally speaking, more rain is falling in areas close to mountains, while less rainfall is being recorded in East Germany and in the Rhine-Main region.

Perhaps the biggest surprise is that global precipitation has not increased in line with global warming. The laws of physics would lead us to assume that these two factors would move in tandem, because air can hold more water in the form of vapor as temperatures rise. For example, at 10 degrees Celsius air can hold 9.4 grams of water per cubic meter when saturated, while at 30 degrees Celsius this fi gure jumps to 30.4 grams – more than three times the amount. Even an increase of just one degree means that the air can hold between six and seven percent more water vapor. And that means the global warning of 0.8 degrees Celsius recorded over the course of the 20th century should have had a notice- able effect on precipitation levels. As an expert in precipitation, Becker argues that it might well be raining more, but that the measuring devices we use are simply failing to highlight this trend.

He points out that precipitation is still measured using a method of calibrated containers that stretches back to the turn of the 20th century. Germany has more than 2,000 precipitation monitoring stations, but the network of stations in many other countries is far patchier. As a result, many localized downpours slip through the net and fail to appear in the fi gures –

even though experts suspect that it is precisely these kinds of localized rainstorms that we would expect to become more common as a result of climate change.

Alternative measuring methods are needed to fi ll the gaps. Precipitation monitoring from space would give us a more rounded picture, but satellite data is too unreliable. So scientists are pinning their hopes on radar equipment, though many countries have yet to in- stall these systems. The GPCC has been evaluating the data collected by radar devices in Germany for the past 11 years, but this period is still too short to offer any reliable indication of trends.

EVERY MILLIMETER COUNTS

Achieving accurate precipitation measurements is an important research goal because each additional millimeter of precipitation leads to an over-proportion- al increase in the risk of fl ooding. This is due to the “sponge effect” of subsurface drainage. More than 50 percent of rainwater never makes it to rivers. Instead, it is

retained by vegetation or absorbed by the soil. However, as soon as the sponge is full, water levels rise more quickly, so any increase can potentially have dramatic consequences: “In saturated drainage basins, a 20 percent rise in precipitation can lead to 50 percent more run-off,” says Axel Bronstert, who holds the Chair of Hydrology and Climatology at the Insti- tute of Earth and Environmental Science at the University of Potsdam.

That means we should certainly expect to see signs of climate change in water level or discharge data. However, statisticians are unable to produce this evidence because the available series of measurements are simply too short.

Determining with a reasonable level of certainty whether a fl ood that used to occur once every 50 years is now happening more frequently would require us to analyze data extending back over several centuries. Yet most data records do not even stretch back 100 years, and scientists have yet to establish an international database of fl ood events.

Nevertheless, there are a number of strong indications that things really are changing. For example, Zbigniew Kund- zewicz from the Potsdam Institute for Climate Impact Research has shown that the number of extreme fl ood events has increased. He reached this conclusion by analyzing data showing when rivers had reached their highest fl ood peak. Between 1961 and 1980, 24 of 70 European rivers reached their record fl ood peak. Over the subsequent two decades, 46 rivers reached their record fl ood peak – almost twice as Bangkok in late

October 2011:

Residents of the Thai capital wade through the streets of the Thonburi district during a flood caused by torrential monsoon rain.

Global precipitation forecasts provide useful insights into the risk of flooding only for large rivers such as the Amazon (pictured). Local factors play a key role in the case of smaller rivers.

intertopics/Photoshot mauritius images/J. Warburton-Lee

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many as in the preceding period. And the situation appears to be similar in other parts of the world.

Once-in-a-century events are occurring with increasing regularity: In 2011, thousands of people perished in fl oods in Pakistan. Meanwhile, Australia has been in the grip of a rollercoaster series of droughts and fl oods. As recently as March 2012, fl ooding in south-eastern Australia reached levels not seen for the past 200 years. The big rain-carrying monsoons are also becoming less predictable. In recent years the monsoon has arrived later than usual in Bangladesh, though its intensity has increased. Another good example of this trend is the Mekong in Southeast Asia, where mean high water levels have been falling slightly while major fl ooding events have become more severe. Upward and downward swings are becoming increasingly pronounced.

The situation may get even worse over coming decades, at least according to the Intergovernmental Panel on Climate Change (IPCC). That’s because emissions of greenhouse gases are rising at a level that experts 20 years ago classed as the worst-case scenario. In 2010, the most recent year for which fi gures are available, global emissions of carbon dioxide from fossil fuels increased by 5.9 percent over the previous year’s fi gure. This re- presents an increase of 49 percent relative to 1990, the reference year for the Kyoto

Protocol. As temperatures increase, so too does the risk of localized heavy precipitation events with 40 millimeters or more of rainfall in a single day. This correlation is now well established.

The IPCC has calculated how many of these severe rainstorms we should expect to see this century. Its recently released report on managing the risks of extreme weather shows that the frequency of intense rainstorms is increasing – from an average of once every 20 years at the present, to once approximately every 15 years in 40 years’ time, rising to at least once a decade by the turn of the 22nd century. The IPCC’s fi gures are averaged over all the world’s continents, so there are signifi cant regional differences. The IPCC is confi dent that we can expect signifi cantly higher precipitation in northern lati- tudes, including Canada, Siberia and northern Europe. It also predicts increased rainfall in Central America, the Amazon region and Australia, though it admits there is far greater uncertainty in this case.

SMALL RIVERS ARE UNPREDICTABLE However eye-catching these kinds of global forecasts may be, they can only indicate general trends. Taken in iso- lation, they provide little insight into the future fl ood patterns of individual rivers, with a few notable exceptions:

Major rivers such as the Amazon and the Mississippi have such enomous drainage

basins that they actually respond roughly in line with the average fi gures that un- derpin the global predictions. However, smaller rivers such as Germany’s Main and Neckar are infl uenced by local factors that may show considerable variation even from one valley to the next.

The problem for water scientists is that global climate models are built at a coarse resolution with grid cells that measure 200 kilometers along each side.

Individual mountains and valleys are simply ironed out on this scale, and the Alps are condensed into a compact strip with an average height of just 600 meters. It is easy to see how this coarse grid approach could be particularly problematic for regions that feature a wide range of different elevations, such as the low mountain ranges found in Germany and many other countries.

That’s why it is so important to scale down global models to incorporate local criteria. Gerd Schädler is one of many scientists engaged in this arduous task.

Based at the Institute of Meteorology and Climate Research at the Karlsruhe Institute of Technology (KIT), his group has conducted research on Central Eu- rope using a climate model with grid cells measuring just 7 x 7 kilometers – a record-beating scale. Because the jump from 200 to 7 kilometers would be too large, the scientists use a 50 kilometer model of Europe as an interim stage.

On December 2011, the Philippines was hit by Tropical Storm Washi. Using radar data from the TRMM satellite, scientists created this 3D depiction of the storm cells, some of which were up to 15 kilometers high (red).

Flooding caused by torrential rain swamped the southern Philippine island of Mindanao, triggering landslips and burying villages under mudslides. Washi killed more than 1,000 people and left thousands more homeless.

NASA/SSAI, Hal Pierce; picture-alliance/dpa

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W E AT H E R A N D C L I M AT E

Using the much fi ner grid to simulate Germany’s climate over the next three decades takes more than a month of processing time on a supercomputer. To obtain halfway decent results, the computer must crunch the data some 20 times using different scenarios and variants.

“We’re certainly keeping our computer resources busy!” says Schädler.

One of the results of this processing marathon is the prediction that the Rhine valley, the slopes of the Black Forest and the Swabian Jura will all experience more frequent heavy summer rainfall events. Yet fi ndings such as these are only the fi rst step toward predicting future fl ood patterns, because not all of the rainwater actually makes it as far as streams and rivers. The next step in- volves applying hydrologic models, which have already been drawn up for many of Germany’s surface water systems. These models describe how much of the surface is sealed, what type of vegetation grows in the area and how quickly the water drains into the subsoil.

ALL THE WAY TO THE SEA

Ultimately, this information enables scientists to determine the extent to which water levels will climb when a specifi ed amount of rain falls. To decide exactly what action to take, however, it is also necessary to apply hydrologic modeling to determine how a fl ood wave will prop- agate along a river to its mouth. This data can then be used to produce fl ood hazard maps that show which buildings are located in critical zones and require precau- tionary measures to be taken.

Obviously all models include assump- tions and uncertainties, and linking together a whole series of models as in this example creates the potential for multiple sources of error. That is why fl ood researchers have spent the last few years repeated- ly running through individual scenarios using a different model each time. These ensemble simulations help to refi ne predictions of what the future may bring.

Nevertheless, their results still cover a wide spectrum, and it is inevitable that these uncertainties will be propagated to subsequent decision-making processes.

That lack of reliable and precise fi gures can make life diffi cult for politicians and

planners. “We have to learn to live with quantifi ed uncertainty,” says Schädler.

This opinion is echoed by one of his Brandenburg-based colleagues: “Models can’t tell us the whole truth, but they can help us edge our way towards it,” says Gunnar Lischeid from the Leibniz Center for Agricultural Landscape and Land Use Research (ZALF) in Müncheberg. Even the best models can’t see into the future;

they can only show us the different ways in which things may develop in the future and the probability of each of these events occurring. Sabine Attinger, who heads up the Department of Computa- tional Hydrosystems at the Helmholtz Center for Environmental Research (UFZ) in Leipzig, is particularly interested in the crucial question of how we can best take into account the uncertainties inherent in hydrologic modeling.

Experts distinguish between large-scale riverine fl oods and localized fl ash fl oods.

When a fl ood strikes large rivers such as the Rhine or the Mississippi, it builds up over days or even weeks, leaving plenty of time to prepare. In contrast, fl ash fl oods happen with little or no warning.

A heavy downpour can be enough to turn a gentle stream into a raging torrent that devours cars and houses within a matter of hours, as the inhabitants of Genoa and Mindanao were unlucky enough to discover. And it is precisely these explosive events – the localized fl ash fl oods scientists say will become more and more prevalent – that are the most fuzzy in the scientists’ models. The biggest challenge for the hydrologists attempting to predict these events is

calculating the “peak fl ow”, in other words the maximum instantaneous discharge in a fl ood event that can cause hazards such as overfl owing dams.

So how will climate change affect the risk of river fl oods and fl ash fl oods? Over 20 global climate models are currently used as a basis for national and regional calculations, yet sometimes even the best models get it wrong. Floods, like volcanic eruptions, evoke a strange psychological response. If 20 years pass without incident, the level of fear gradually diminishes and there is less of an urge to take precautions.

But when a fl ood does fi nally strike, there is a strong feeling that everything should be done as quickly as possible.

TAKING PRECAUTIONS REQUIRES EXPERTISE The Philippines is a perfect example:

Following the devastation caused by Tropical Storm Washi, in which many victims were swept away without warning, the country’s president made a personal visit to the university to exert pressure and to allocate the necessary funding for an early warning system. The plan is to set up a fl ood forecasting center within a 12 month timeframe. Yet this goal seems almost completely unrealistic given that it cannot be achieved with a supercomputer and software alone, but rather requires a range of infrastructure including meteorological and hydrologic monitoring stations, reliable data on vegetation, soil types, ground sealing and numerous other aspects and, of course, properly trained experts who are capable of evaluating this data. Unfortunately these kinds of improvements are often Even Germany cannot escape major flooding unharmed. The Elbe flood in April 2006 temporarily transformed the historic town of Hitzacker in Lower Saxony into an island.

picture-alliance/dpa

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not introduced until disaster has already struck. The government’s purchase of rain radar systems is certainly a positive step forward, but only if staff are properly trained will they actually be able to calculate precipitation from the radar data and use this as a basis for predicting possible fl ood fl ows.

Flood forecasting is often also hampered by political confl icts. Since rivers do not tend to respect national borders, fl ood management typically requires

international cooperation. The example of the Rhine shows just how well neighboring countries can work together when they set their minds to it (see

“Everyone wants their share” starting on page 22) – but this doesn’t mean that things always run so smoothly.

The countries involved in these sit- uations are typically reluctant to fully disclose how water levels are evolving.

This secretiveness can have fatal consequences in the event of a fl ood because it is impossible to model a fl ood wave without accurate data from further up- stream. This is a problem that affects the Indus, which fl ows through the hostile neighboring countries of India and Paki- stan, as well as the Nile and the Euphra- tes. Even on a national level, research and risk management efforts can sometimes be hampered by the failure of scientists and local authorities to share the data they have collected.

POLITICIANS MUST ACT

At the end of the day, scientists can only give recommendations. Experts are certainly capable of calculating where fl oods are likely to occur and how climate change is affecting fl ood events, but Friedemann Wenzel from the Geophys- ical Institute at the Karlsruhe Institute of Technology (KIT) argues that “these efforts will only bear fruit if people appre- ciate how necessary they are”. Politicians need to act, for example by building or raising levees, creating fl oodwater re- tention areas, limiting development in fl ood-prone areas and ensuring crisis management teams have the necessary tools at their disposal.

All too often there is a failure to com- municate crucial information to the public. Bruno Merz, a fl ood expert from the German Research Center for Geosciences (GFZ) at the Helmholtz Center Potsdam, conducted a survey of 2,000 households that suffered damage in the Elbe fl ood in 2002. The results showed just how ineffective the warnings had been. Ac- cording to Merz’s fi ndings, there was no difference between the victims who had been warned and the victims who had been caught completely off guard. Most of them would have had no idea how to respond to the danger anyhow. n

REGIONAL CLIMATE SIMULATION FOR HEAVY RAINFALL EVENTS

A research group headed by Gerd Schädler at the Institute of Meteorology and Climate Research at the Karlsruhe Institute of Technology (KIT) has scaled global climate models down to a regional level. The researchers used their COSMO-CLM regional climate model to provide data on a portion of central Europe with a resolution of just 7 kilometers. The diagram above, which covers some two thirds of Germany, shows how likely it is that heavy summer precipitation events will change in the future. The two periods compared are 1971 to 2000 (“present”) and 2011 to 2040 (“near future”). Shades of dark blue indicate regions that face an increased likelihood of heavy precipitation in the future, such as the Eifel region at top left. Shades of brown – such as those in the Vogelsberg/Rhön mountains at the center of the map – indicate that heavy rainfall events will become less likely.

Accurate precipitation data: This 34 meter high weather radar tower is located on the

Sophienhöhe hill in Hambach and forms part of the Jülich Research Center.

Latitude in degrees north

Longitude in degrees east

Probability of change in percent

Jülich Research Center

Feldmann, H., Schädler, G., Panitz, H.-J., Kottmeier, Ch., 2012: Near future changes of extreme precipitation over complex terrain in Central Europe derived from high resolution RCM ensemble simulations. International Journal of Climatology (accepted)

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F O R E C A S T F O R G E R M A N Y

Future

scenarios

Climate change will affect precipitation patterns in Germany. Hydrologists are using complex system models to ﬁ nd out where droughts or fl oods might occur in the future.

BY UTE KEHSE AN EMPTY STRETCH OF SHORELINE, some

fi ve meters wide, surrounds the Rederns- walder See, a lake in the north-eastern part of Brandenburg. Satellite images clearly show that this empty strip at the edge of the lake, where blades of grass poke their way between the grains of sand, was completely covered by water up until just a few years ago. Since 1980, the water level has fallen by three meters and the volume of water in the lake has been halved. And this isn’t the only example: Many other lakes in this pro-

tected area, known as the Schorfheide- Chorin Biosphere Reserve, have also been shrinking over recent decades. Jetties end before they reach the water, new islands are appearing, and shallow bays are gradually morphing into raised bogs, all of which indicates one thing: The amount of groundwater feeding these lakes has dropped drastically.

So is this a consequence of climate change? After all, records show that the temperatures in Brandenburg have been increasing over the last few decades, and

summer precipitation has decreased slightly – two factors that lead to slower replenishment of groundwater reserves.

Yet the reality is more complex: A study conducted in 2010 by a group of researchers led by Gunnar Lischeid at the Leibniz Center for Agricultural Landscape Re- search (ZALF) in the Brandenburg town of Müncheberg yielded some surprising results, revealing that water is also being sucked out of the soil by the forest. “In the north-eastern part of Brandenburg we have lots of pine monocultures

J. Lösel for bdw

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Future

scenarios

Working in VISLab, the Visualization Center of the Helmholtz Center for Environmental Research (UFZ) in Leipzig – Luis Samaniego (left) is an expert in modeling hydrological systems.

Projectors project computer-generated images onto the back of the glass screen and use 3D effects to provide insights into deep-lying rock strata. Scientists use a flystick – the device held by Samaniego’s colleague in the background of the picture – to take a virtual “flight” through the aquifer.

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F O R E C A S T F O R G E R M A N Y

that were planted at the end of the Second World War,” says Lischeid, who heads up the Institute of Landscape Hydrology at ZALF. Coniferous forests are constantly thirsty, and pines need more water the older they get. They also drink more than deciduous trees because their needles release water into the atmosphere all year long.

Lischeid and his colleagues hit upon this unexpected fi nding using model calculations. The standard approach in hydrology is generally to depict each process in the water balance in a sepa- rate model. But Lischeid and his team decided to carry out their study by cou- pling together two different models:

A water balance model that calculates how much groundwater recharge is taking place while taking into account the behavior of the vegetation, and a groundwater model that can subsequently be used to calculate water levels in the lakes. The results of this coupled model approach confi rmed that the cause of the falling lake water levels can be attributed approximately 50/50 to vegetation and climate.

TWOFOLD BENEFIT OF DECIDUOUS FORESTS The researchers’ next step was to in- vestigate whether this trend could be halted if the pines were replaced by deciduous trees such as oak and beech. This led them to discover a further unexpected effect. “Converting forests is an even more effective solution than we initially anticipated,” says Lischeid. Their calculations showed that less grass grows between trees in deciduous forests than in the more open pine forests – which re- duces water consumption even further.

The researchers concluded that replac- ing coniferous forests with deciduous forests could at least partially balance out the effects of climate change.

Lischeid and his colleagues are part of a new trend in hydrology in which hydrologists are increasingly developing more holistic, integrated models that incorporate multiple sub-processes of the hydrologic cycle. For example, scientists studying the dispersion of pollutants need to know more than simply how fast substances seep into the soil. They also have to take into account how often and how heavily it rains, which cultures are growing in a fi eld, how fi rmly the soil is compacted and how much water runs off the surface. Just like climatologists, hydrologists want to make forecasts for the decades ahead – and for that they will need these kinds of integrated process models.

“Models are the only method we have of looking into the future,” says Olaf Kolditz, Head of the Department of Environmental Informatics at the Helm- holtz Center for Environmental Research (UFZ) and Professor of Applied Environ- mental Systems Analysis at Dresden University of Technology. Complex models spell the end of the simplifi cations that are still favored by many scientists.

Currently, many processes on the land surface and in the soil zone are incor- porated in climate models only in their most rudimentary form. At the same time, groundwater models pay relative- ly little attention to the atmosphere. “Of course in reality there is obviously interaction between all the various parts of the water cycle,” says Kolditz. “Using coupled hydrosystem models enables us to gain a better understanding of the systems involved, because we can break down their complexity.”

Models are simple computer programs that use mathematical equations to calculate how defi ned parameters change over closely spaced intervals of time at multiple points in space. To apply this method to the water cycle, researchers fi rst have to defi ne the points in their model area where they wish to determine physical parameters such as soil moisture, water levels, fl ow veloci- ties in surface waters and groundwater, pollutant concentrations, and temperatures. To do this, they defi ne what is known as a grid, a pattern consisting of multiple points on a two-dimensional

Future scenarios

Modeling soil moisture in Germany, 2003. A fall in the soil moisture index (SMI, scale at bottom) to 0.2 or lower indicates extremely arid conditions. The researchers’ goal is to make reliable predictions of droughts.

0.1

0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

June 2003

December 2003 February 2003

L. Samaniego/UFZ (3)

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Future scenarios

surface or in a three-dimensional space at which the readings will be taken.

To perform the actual calculations, researchers can choose between two different approaches, namely using physical formulas or employing empirical data. “The fi rst approach produces what we call process-based models, and the second approach conceptual models,”

Kolditz explains. Both methods have their advantages and disadvantages:

Conceptual models are well suited to depicting the multiple behaviors of a complex system and are easier to manage.

However, their predictive power is lim- ited by the fact that they are based on observations, which means that they can, as a rule, only reproduce patterns based on past experience.

In many cases, hydrological processes are represented by a single fi gure re- ferred to as a parameter. “The challenge is fi nding the best parameter for each process,” says Luis Samaniego from the UFZ. In contrast, process-based models are more precise but also more compli- cated because they require signifi cantly

more measurement data as input – data which in many cases is unavailable. In the fi eld of hydrology, surface runoff is generally depicted using conceptual models, while soil and groundwater are modeled using process-based models.

Over the last two years, Luis Samaniego and his colleague Rohini Kumar have developed a hydrologic model for the whole of Germany that they are hoping to use in the future to predict droughts and potential fl ooding.

SOIL MOISTURE IS THE KEY

One of the cornerstones of their model is soil moisture. This is a key issue for farmers because plants cannot grow unless there is enough water available at their roots. Previously, however, there was no model capable of forecasting which part of Germany might be hit by a drought in the near future; fi rst, because there is no comprehensive system in place to take measurements, and, second, because soil moisture depends on so many different factors. Determining how much precipitation will seep into the soil and how

much will evaporate requires knowledge not only of the weather, but also of soil characteristics, topography and vegetation. “When you get heavy summer rain falling on soil that has a high clay content, most of the water runs off the surface, further accelerating what- ever erosion has already taken place. In contrast, periods of lighter rain allow the water to soak deeper into the subsoil,”

says Samaniego.

The model developed by Samaniego and Kumar links up the processes in the atmosphere, the biosphere and the ‘pe- dosphere’ – the outermost skin of the Earth, just a few meters deep and largely composed of topsoil. A further factor taken into account in the calculations is the growth phase of the vegetation. The result yielded by the model is known as the soil moisture index, which indicates whether a specifi ed place is currently experiencing drought conditions or not.

To test their model, the researchers entered data for the period between 1950 and 2010. The periods of drought calculated by the model corresponded

VISLab journey through the substrate of the Thuringian Basin – the area shown on the screen measures approximately 150 by 75 kilometers. The various rock strata are shown in different colors.

J. Lösel for bdw

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F O R E C A S T F O R G E R M A N Y

balance of entire continents. Equally, some models are based on time scales measured in seconds, while others stretch to centuries.

Another of the researchers’ future goals is to incorporate more satellite data into their models, such as data on vegetation or, further into the future, on soil moisture (see box on “Monitoring water from space” on page 41). “The only downside to this wealth of data from space is that it makes our models so complex that we need tremendous computing power. But the upside is that our model forecasts should become far more accurate,” says Kolditz on a positive note.

THE IMPORTANCE OF PARALLEL PROCESSING In order to harness the full potential of modern supercomputers, hydrologists also need to rethink some of their methods. The fastest computers in the world today, such as the JUGENE supercomputer at the Jülich Research Center, contain several hundred thousand parallel processors. To make best use of them, the programs used in the hydrologic models must be designed to run multiple calculation steps in parallel, rather than consecutively as on normal computers.

“Unfortunately the programs we currently have are still not capable of running effi ciently on supercomputers,”

says Kolditz. The Helmholtz Association recently launched an initiative aimed at improving the development of scientifi c software. At the UFZ, the development of the OpenGeoSys software, which is used by a number of research groups worldwide, lies in the capable hands of the computer scientist Lars Bilke.

Often it is only with the development of new and more complex models that researchers can get to the bottom of seem- ingly inexplicable trends – for example the shrinking lakes of Brandenburg.

In this context, scientists use the term

“non-linear correlations” to describe how, under certain circumstances, minor changes can have a whole series of consequences that then have domino effects on each other. “You can’t assume that when you change one parameter everything else simply stays the same,” says Lischeid.

To achieve their near-term goal of producing more accurate forecasts for the future, hydrologists are particularly dependent on their collaboration with the climate researchers whose models yield the data required as input for hydrologic models. Yet even this approach is not clear-cut: “Climate models are good at forecasting temperatures but not so good at forecasting precipitation,” says Lischeid. “For areas measuring a few hundred square kilometers, which is the size we need for hydrological research, current climate models are not really capable of providing reliable forecasts.”

Clemens Simmer at the University of Bonn is working on ways of overcoming this problem. “Our goal is to fi nd ways of developing fully coupled model systems that are capable of physically modeling the hydrologic cycle from groundwater to the atmosphere and back again, starting at a regional scale of a few hundred kilometers,” says the meteorologist. The model system developed by the Trans- regional Collaborative Research Center TR32, which Simmer runs at the Ger- man Research Foundation (DFG), cou- ples together the COSMO regional climate and weather forecast model with the CLM Community Land Model and the ParFlow hydrologic model. A second, highly detailed model calculates the movement of water over areas of between 10 and 20 kilometers with grid points just meters apart.

Simmer and his colleagues are hoping to signifi cantly curb the use of empirical values to describe complex physical processes. This is a key step without which many observations cannot even be used for forecasts. “For example, I can only run a model with observed soil moistures if that model offers a real- istic representation of water fl ow,” says Simmer.

HOW THE SOIL AFFECTS THE WEATHER The Bonn-based scientists are particularly interested in creating more accurate models of the interaction between the land and the atmosphere in order to better understand precipitation. In many cases, of course, the soil – the outermost layer of the Earth’s skin – has no impact closely to the actual recorded drought

conditions. The most intense periods of drought occurred in the summer of 2003 and the winter of 1952/53, while the longest recorded dry spell occurred in the early 1970s, spanning a period from August 1971 to July 1974 and affecting virtually the whole country. Kumar and Samaniego now intend to feed current climate data into their model and hope to produce drought forecasts for the months ahead.

Plans are also underway to couple the soil moisture model with the Open- GeoSys program developed by Kolditz and his team, which simulates thermal, hydrological, chemical and mechanical processes in soil and groundwater. Yet linking together different models throws up some signifi cant challenges. The least of these is the fact that the models may have been written in different programming languages – but an even bigger challenge is puzzling out how to effect seamless transfers between models without data going astray. Some models calculate the fl ow of water in tiny vol- umes of just a few cubic millimeters, while other models simulate the water

Future scenarios

Many of the lakes in Brandenburg have shrunk, leaving a dry strip of shoreline like this one on lake Knochensee. But the climate only shoulders half the blame – see the picture at bottom right.

H. Mauersberger, Schorfheide-Chorin Biosphere Reserve

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HYDROLOGIC MODELS IN 3 D

Next-generation coupled hydrologic models provide all sorts of data – not just graphs and simple diagrams, but also three-dimensional datasets that can even show changes over time. The wide-ranging results can be displayed in VISLab, the UFZ’s Visualization Center in Leipzig (see photos on pages 12/13 and 15). VISLab uses 13 projectors to project graphical data onto the back of a large glass screen. With the aid of special glasses, viewers are presented with different images for their right and left eyes that change at rapid intervals, tricking their brains into believing that they are seeing in three dimensions. This creates a kind of virtual reality in which the three-dimensional images of rock strata, water flows and wind parks change perspective as the viewer changes position.

“This 3D visualization process makes complex data and processes visible and simpler to grasp. That makes it easier to incorporate large, multifaceted datasets and discuss them with other scientists,” says Lars Bilke from the UFZ, who runs VISLab.

on the current weather, for example if new areas of low pressure are moving across Germany every day. “In these situa- tions the atmosphere doesn’t register the composition and small-scale features of the Earth’s surface,” says Simmer. But things look very different when it comes to localized summer storms, which are often fed by the local soil moisture.

“That’s when the soil can have a really significant impact. Even groundwater depth can play a role in these events,”

explains the meteorologist.

In order to model these effects, researchers first need data – for example on precipitation – of the highest possible quality and accuracy. Yet, astonishingly, this kind of data is currently not recorded on a comprehensive basis. Although con-

ventional radar measurements can detect where it is raining, they can provide very little information on how much precipitation reaches the soil and whether it has fallen as drizzle, torrential rain, hail or snow. “In terms of quantities, some of the data has error rates of 100 percent,”

says Simmer. Equally, weather stations are spread too thinly to provide the kind of accurate measurements that hydrologists would like to see.

This is why Simmer is collaborating with the Helmholtz Research Initiative TERENO (TERrestrial ENvironmental Ob- servatories, see page 25) and the Hans Ertel Center for Weather Research (HErZ) program initiated by the German Meteo- rological Service (DWD) to work on new methods of measuring precipitation

more accurately. For example, rainfall radars could use polarized signals to provide information on the size of rain- drops and the type of precipitation. The models developed by the researchers in Bonn are currently still at the test phase.

“We’re hoping to achieve better climate forecasts as well as improved weather forecasts,” says the meteorologist.

They have already produced their first rough forecasts of precipitation for Brandenburg, the driest of Germany’s federal states. “Our figures suggest that the developments we’ve seen over the last 20 to 30 years will continue,” says Lischeid. Precipitation will continue to decrease in the summer and increase in the winter. Heavy downpours will become more frequent than they are today, as will longer periods of drought.

“The effects on agriculture won’t actually be that dramatic, because the CO₂ content of the air is increasing at the same time, and that will make plants grow better,” he says reassuringly.

Lischeid refuses to be pinned down to exact predictions of future precipitation levels. “It’s hard to say whether we’re talking about 50 millimeters more or less – making predictions of that kind would be a bit like reading tea leaves,” says the researcher. And that’s not the only lesson he’s learned from his past work: “On a local scale, climate change certainly plays a role, but other effects may be more significant.” n

Model calculations have revealed that Brandenburg’s typi- cal pine forests – and the grass growing between the trees – consume significant quantities of water, which makes them a key cause of lakes drying out.

How will climate change affect the soil?

Hydrologists cover a test zone with panels at the Schorfheide-Chorin Biosphere Reserve.

Caro/Teschner; ddp images/dapd/T. Heimann

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E N V I R O N M E N TA L C O S T S

Scientists use many different approaches to assess the value of water, such as determining appropriate pricing models, optimizing water management, and analyzing the importance of water for ecosystems.

worth?

BY FRANK FRICK 1,000 LITERS OF DRINKING WATER – is

worth...how much? If you live in Bonn or Düsseldorf, the answer is approximately 3 euros – that’s how much households in North Rhine-Westphalia were charged for 1,000 liters in 2010 according to the German Federal Statistical Offi ce.

In contrast, a Bavarian household paid just 1.86 euros for the same quantity.

“There’s a concern that the prices in some places are infl ated by inescapable regional monopolies,” says Erik Gawel, an economist at the Helmholtz Center for Environmental Research (UFZ). He adds:

“In economic terms, the only sensible pricing policy is one that is free from monopolistic interference.” And that’s not all: Gawel also fundamentally be- lieves that the price should compensate drinking water producers fairly for their work, and that it should acknowledge the true environmental cost by refl ecting the fact that human water consumption affects the natural water cycle.

In fact the European Water Frame- work Directive already obliges EU mem- ber states to take environmental costs into account when setting the price of

water services. Countries in the EU are also required to set reasonable price in- centives to ensure that water resources are used effi ciently. In other words, the price should be high enough to ensure that consumers learn to use water reasonably sparingly.

Yet not everyone agrees with this ob- jective: For example, the German water utility RWW, which is headquartered in Mülheim an der Ruhr, argues that “there’s no reason to use water sparingly – it makes no environmental or economic sense.” Gawel disagrees: “It’s true that we currently only use what seems like a small proportion of our fresh water sup plies – just 17 percent of the 188 billion cubic meters available in Germany each year – but that still has an environmental impact on our water-carrying systems.

That’s why we talk about water stress as soon as that fi gure climbs above 20 percent.” In some regions of Germany, this 20 percent limit is already being exceeded.

And regardless of the fact that there is essentially enough water available on a global scale, it wouldn’t take much for

The Wupper has many uses: The river defines the route of the Wuppertal Sus- pension Railway (above) and offers a perfect setting for kayakers as well as being a drinking water reservoir and important biosphere.

Wupperverband (5)

worth?

What is water

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water to become a scarce resource in certain regions at certain times – especially if we consider the potential consequences of climate change. Gawel goes on to make the point that water can still be a scarce resource in economic terms, even in the absence of immediate water shortages:

“It’s like bread or cell phones: Neither of those things are in short supply in Germany, yet there are still certain limits on their availability, and that’s why they have a price that reasonably refl ects the scarcity of the resources used to produce them.”

A further point of contention is the extent to which the prices in Germany actually refl ect the environmental costs involved. Most of Germany’s federal states charge a water extraction fee for this purpose, and the central government The idyllic building known as the Wipper- kotten used to be a grinding shop which used water from the Wupper to power its water wheels.

A prime example of successful river basin management – from the source (on the right edge) to where the Wupper flows into the Rhine (far left).

One of eleven: The Buchenhofen sewage treatment plant (left) treats Wuppertal’s wastewater. Operating the treatment plants is one of the jobs of the Wupperverband association – but it is equally concerned with ecological issues and the joys of fishing.

also charges a wastewater levy. Yet at 4.5 cents per 1,000 liters, the water extraction fee charged in North Rhine-Westphalia only plays a minimal part in the price difference between North Rhine-West- phalia and Bavaria.

Additional taxes and higher water prices have never been popular with consumers.

“Both private individuals and companies

tend to measure the value of water in just one dimension, i.e. money, while neglect- ing to consider indirect cost factors,” says Janos Bogardi, who heads up the Interna- tional Project Offi ce of the Global Water Systems Project in Bonn. He argues that the consequences of this attitude are clear: “In practice, it prevents us from using water in a sustainable way.”

The Wupperverband: a model

Drinking water dam nine process water dams Municipal dams

Operated by Wupperverband Headquarters

Depots

Marienheide Hückeswagen Radevormwald Schwelm Buchenhofen

Kohlfurt Burg Leverkusen Odenthal Wermelskirchen Dhünn

11 10 2

3 4 5

6 7 8 9 1

blickwinkel/H. Pieper Wupperverband

Wastewater treatment plants

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WA S S E R R E S S O U R C E N

are better at breaking down contami- nants and nutrients, which means they have superior self-cleaning properties compared to systems with reduced biodiversity,” says Haase. Bank fi ltrate is pumped from wells in close proximity to rivers and lakes. The greater the natural cleanliness of the water from the river or lake when it reaches the well, the lower the costs of treating it.

Bernd Wille, the Chairman of the Wup- perverband, an association that manages water resources in the Wupper river basin, expresses this in even more general terms:

“Water systems only retain their value and usefulness in our lives if they are ecologically intact.” The members of the Wup- perverband include municipal and district authorities, water supply and wastewater disposal utilities, businesses and indus- trial concerns in the Wupper’s catchment basin, which totals 813 square kilometers.

The association, which is a public corporation thanks to special legislation passed in North Rhine-Westphalia, manages 12 dams and 11 wastewater treatment plants. “But we’re much more than just a plant operator,” Wille empha- sizes. “We see ourselves as a river basin management team that takes a holistic, integrated view of water, people and the environment.” Many experts agree that the association is setting a laudable example, for three key reasons:

• Instead of carrying out its activities within narrow political borders, in this case municipalities, the Wupperverband acts throughout the Wupper basin.

• It has long favored a system of round- tables where representatives of all the key players in the river basin come together to participate in the decision-making process.

• “The key responsibilities are spread among multiple authorities and companies, plus the representatives they send change on a frequent basis, so you need an effi cient knowledge management system,” says Wille. The Wupperverband utilizes a number of solutions including what it calls a river basin geoinformation system (FluGGS in its German abbrevia- tion), which makes location-dependent environmental information rapidly available over the internet.

Wille is convinced that the Wupper- verband sets “a great example for the rest of the world”, and he stresses the importance of research. “Modern water management is entirely dependent on good

E N V I R O N M E N TA L C O S T S

As an economist, Gawel takes a clear stance on this issue: “Water use charges offer a unique value-added benefi t as part of water pollution control policies in a market economy. They should be main- tained – or even expanded,” he says, ar- guing that taxing farmers who introduce fertilizers and pesticides into the water system would offer a particularly effective way of preventing water pollution.

DECLINE IN BIODIVERSITY

Considering that 70 percent of surface waters in Germany are currently in poor ecological health, his argument is sound, and entirely pragmatic. “Human activities are causing a greater loss of biodiversity in our lakes and rivers than on land or at sea,” notes Peter Haase, who heads up the Department of River Ecology and Conservation at the Senckenberg Research Institute and Natural History Museum in Frankfurt. This is particularly worrying in light of the remarkably important role that lakes, rivers and swamps play in global biodiversity.

Although they hold less than one ten-thousandth of the volume of water on Earth, scientists estimate that they provide a home to some 12 percent of all known species. One place where this has been particularly well studied is the river Breitenbach near the Hessian town of Schlitz. Scientists from the Limnological River Station run by the Max Planck Institute for Limnology have identifi ed more than 1,000 animal species during their decades of research there, more than half of which are aquatic insects.

Keeping surface waters ecologically intact is important, especially for the millions of Germans who get their drinking water from bank fi ltrate. “Surface waters with high levels of biodiversity

Hydrologist Christine Engelhardt collects a sample of water from the Elbe. In the process she records all the animal life that is visible to the naked eye.

A sexually mature adult mayfly (Rhithrogena picteti).

It only lives for a few days – just long enough to mate and lay its eggs. Its presence is a clear bioindicator that this stream is in good ecological health!

Senckenberg (5)

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research,” he says, citing as an example certain sections of the Wupper in which the water stagnates behind dams while being heated to unnatural levels by power plants and polluted by contami- nants from urban areas. “Only research work can help us determine what measures are worth taking to improve the ecological health of these sections of water and enhance their value.”

MIXED RESULTS

These kinds of issues form the crux of the work carried out by Peter Haase and his team of scientists at the Senckenberg Research In- stitute. In one recent project they surveyed the success rate of 24 projects conducted over the last 12 years to restore sections of German rivers to their natural state. The results were sobering: On average, the initiatives resulted in only slight improvements to the biodiversity and number of organisms in the restored areas.

However, in cases where valuable in- vertebrates had settled within a radius of less than fi ve kilometers prior to the restoration project, this subsequently had a positive effect on the ecosystem in the restored section of the river. “It seems likely that many organisms only migrate back to a restored river or lake if it is close at hand,” says Haase, out- lining their conclusions.

The complex interplay between biotic communities, water quality, external factors and the value of water is constantly giving rise to new research topics. For example, over the last 15 years scientists

have noted that the concentration of organic carbon is increasing in many bodies of water all around the world, presumably as a consequence of global climate change. This poses a problem for drinking water treatment plants which

use chlorine to disinfect the water, because the organic carbon leads to the formation of problematic by-products.

This is just one of the resons why the UFZ is installing complex measuring equipment at the Rapbode Dam in Saxony-Anhalt. “Our aim is to monitor the entire ecosystem of this major drinking water reservoir – Germany’s largest –

over a period of years,” says Karsten Rinke, who heads up the Department of Lake Research at the UFZ. The scientists hope this will enable them to produce reliable forecasts of how carbon concentrations will develop in the future, as well as helping them to develop strat- egies to reverse this trend.

Organic carbon is also on the agenda for researchers at the Leibniz Institute of Freshwater Ecology and Inland Fish- eries (IGB). “Our Terralac experiment

aims to show what effect organic carbon has on the ecosystem and the food

web in shallow lakes and how it im- pacts water quality,” says project

manager Sabine Hilt. To conduct the experiment, she selected two lakes in Brandenburg, both 3 hec- tares in size but exhibiting important differences: One of the lakes is dominated by algae growth which makes it appear murky, while the other lake has clear water and is mostly populated by higher aquatic plants.

In 2010, the scientists split each lake into two halves using tarpaulins. In one half of each lake they then simulated an increased input of organic carbon by adding corn leaves. The team still hasn’t fi nished evaluating all the data from the experiment, says Hilt, “but our fi ndings indicate that the organic carbon is better utilized in the food web of the clear lake than in the algae- dominated lake.” This is an interesting fundamental insight, she argues, and perhaps that’s not all – it could also serve to remind us just how careful we should be to maintain our valuable clear water lakes in the future. n For a long time the Nidda flowed through Hesse as a straightened canal (left). Since being restored to a more natural state, its banks have regained some of their original character. Yet researchers caution that biodiversity does not always benefit from these.

Pretty as a picture:

the larvae of the stonefly (Perla marginata). More than 500

species of aquatic insects live in intact river ecosystems.

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WAT E R C O N F L I C T S

Everyone Everyone

wants their share

THE KIDRON VALLEY, known in Arabic as Wadi Nar, begins in the center of Jerusa- lem and continues some 25 kilometers eastward through a gorge in the middle of the Judean Desert all the way to the Dead Sea. “When I came to Israel for the fi rst time in 1993 I was tempted to hike along it – before the First Intifada in 1987 it was very popular with Israelis as a hiking trail,” recalls Ines Dombrowsky from the German Development Institute in Bonn.

Most of the Kidron Basin belongs to the West Bank. Nowadays it passes through three zones designated as A, B and C in which the Palestinian Authority and the Israeli military each have various powers of authority. Yet it is not only the security situation that discourages people from hiking through the Kidron Valley. An open rivulet of untreated sewage fl ows along its course, carrying some 9 million cubic meters through the valley each year. Most of this wastewater comes from

the eastern side of Jerusalem which is home to some 165,000 Israelis and Pal- estinians.

“The wastewater smells terrible and obviously poses a major risk to health and the environment. It pollutes the groundwater and the Dead Sea,” says Eyal Hareuveni from B’teselem, an Israeli human rights organization. In the view of Abdelrahman Tamimi, an expert from the Palestinian Hydrology Group for Water and Environ- mental Resources Development, the smell is far from being the worst of it: “The fact that there is no wastewater treatment plant means that water is simply being wasted that could otherwise be put to good use in this very arid region.”

The Palestinians could certainly do with the treated water, especially for crop

Social scientists can help when countries are at loggerheads over transboundary rivers or when domestic disputes fl are up over the equitable use of water resources.

BY FRANK FRICK

in Bonn. year. Most of this wastewater comes from with the treated water, especially for crop

0 to 500 501 to 1000 1001 to 1700 1701 to 5000 5001 to 10 000 10 001 to 50 000 50 001 to 100 000 100 001 to 1 000 000 1 000 001 to 5 000 000

> 5 000 001

Quantity of water available in cubic meters per capita and year

Product of the Transboundary Freshwater Dispute Database, Department of Geosciences, Oregon State University