Climate Change in Southern GermanyExtent – Impact – Adaptation

CONSEQUENCES FOR WATER

RESOURCES MANAGEMENT

Bayerisches Staatsministerium fürUmwelt und Gesundheit

LUBW Landesanstalt für Umwelt,

Messungen und Naturschutz

Baden-Württemberg

[Baden-Württemberg State Institute for the

Environment, Measurement and Nature

Conservation]

Griesbachstraße 1, 76185 Karlsruhe

Bayerisches Landesamt für Umwelt

[Bavarian State Agency for the Environment]

Bürgermeister-Ulrich-Str. 160

86179 Augsburg

Landesamt für Umwelt, Wasserwirtschaft

und Gewerbeaufsicht Rheinland-Pfalz

[Rhineland-Palatinate State Department of the

Environment, Water Management and Trade

Supervision]

Kaiser-Friedrich-Straße 7, 55116 Mainz

Deutscher Wetterdienst

[German Weather Service]

Frankfurter Straße 135, 63067 Offenbach

Further information may be found at:

www.kliwa.de

www.um.baden-wuerttemberg.de

www.stmug.bayern.de

www.mulewf.rlp.de

www.lubw.baden-wuerttemberg.de

www.lfu.bayern.de

www.dwd.de

www.luwg.rlp.de

1 THE EARTH’S CLIMATE 4

2 REGIONAL CLIMATE CHANGE 6

3 INSTRUMENTS OF CLIMATE RESEARCH 8

4 TOMORROW’S CLIMATE 10

5 WATER BALANCE MODELS 12

6 GROUNDWATER 14

7 LOW WATER 16

8 FLOODING 18

9 HEAVY RAINFALL 20

10 AQUATIC ECOSYSTEMS/OUTLOOK 22/23

KLIWA (KLIMAVERÄNDERUNG / WASSERWIRTSCHAFT) STANDS FOR CLIMATE CHANGE AND ITS IMPACT ON

WATER RESOURCES MANAGEMENT.

KLIWA IS A COOPERATIVE PROJECT INVOLVING THE FEDERAL STATES OF BADEN-WÜRTTEMBERG, BAVARIA

AND RHINELAND-PALATINATE AND DEUTSCHER WETTERDIENST [GERMAN WEATHER SERVICE].

commissioned by

Ministeriums für Umwelt, Klima und

Energiewirtschaft Baden-Württemberg

[Baden-Württemberg Ministry of the Environ-

ment, Climate Protection and the Energy Sector]

commissioned by

Bayerischen Staatsministeriums

für Umwelt und Gesundheit

[Bavarian State Ministry of the Environment and

Public Health]

commissioned by

Ministeriums für Umwelt, Landwirtschaft,

Ernährung, Weinbau und Forsten

Rheinland-Pfalz

[Rhineland-Palatinate State Ministry of the

Environment, Agriculture, Food, Viticulture and

Forestry]

Planning and realisation

ÖkoMedia GmbH, Stuttgart

Frontpage Satellite Pictograph:

Deutscher Wetterdienst/EUMETSAT

Status: November 2012

this publication was printed using a carbon-

neutral process

CONTENTS

3

FOREWORD

Water is one of the most valuable gifts of nature. We all live by water and withwater. Water management carries a heavy load of responsibility. On the onehand it must ensure that water functions as the indispensable foundation of life,on the other it must protect people against the potential threat that it represents.Standards of water management in Germany are high. We are protecting ourwaters and improving them wherever necessary. We have sufficient good qualitydrinking water, and we are investing millions in flood protection.

But the water cycle is in a state of flux. With climate change, our water resour-ces are changing as well. We know today that temperatures are rising all overthe world as a result of the greenhouse effect, and this process is set to contin -ue. We will no longer be able to halt these developments, but we must try tokeep the effects of the changes under control with the help of a consistent andeffective climate protection strategy.

As a consequence of climate change, we must anticipate an increase in the inci-dence of extreme weather events. In all probability the future will see more fre-quent heavy rainstorms, but there are also likely to be more heatwaves and peri-ods of drought. Water management must adapt accordingly, and try to find newways of coping with these developments.

Thanks to KLIWA we are now in a position to estimate approximately how cli -mate change will affect flooding, low water and our groundwater reserves. Ofcourse there continue to be some grey areas. We must evaluate these accurate-ly while setting the points correctly for the future, and this is a major challenge.But even in terms of fundamentals there is a need for action. How will climatechange affect the water quality of our streams and rivers? What adjustmentsmay turn out to be necessary?

A consistent climate protection strategy, at global, national and regional levels,will enable us to keep the consequences of climate change within calculablelimits. The emission of greenhouse gases must be checked as far as possible.Where the effects can no longer be reversed, we must respond by making thenecessary adjustments. This means preparing climate-sensitive systems for thechanges in the best possible way. To ensure that this happens, the adaptability of our ecosystems must be increased and their vulnerability reduced, and wemust go on consistently extending our current pool of expert knowledge on climate change and its consequences. The KLIWA cooperative project is makingan important contribution in this connection.

Bayerisches Staatsministerium fürUmwelt und Gesundheit

Increasing incidence of weather extremesThe Earth’s climateThere was a marked increase in the number of extreme weather events in the early 1990s. In 2003, Europe groaned

for weeks under temperatures as high as 40°C. Two years later, in August 2005, the Alpine Foothills were completely

submerged following extreme and persistent rain. The occasionally spring-like temperatures of winter 2007/2008

were followed by snowy winter months and severe frosts in December 2010. There was literally no precipitation at all

in November 2011. Is the increasing frequency of unusual weather events simply a coincidence?

... OR IS CLIMATE CHANGE ALREA-

DY A REALITY?

The Earth’s climate has varied naturally overthe course of millennia. At times Europeenjoyed a tropical climate, at others it wascovered by massive ice sheets. Sedimentdrill samples and pollen analyses yield in -sights about climate fluctuations in early phases of the Earth’s history. Weather datahave been recorded on a regular basis since1860. Evaluations of these data reveal thatthe mean global temperature has risen byaround 1°C over the last 150 years. Althoughthis may not appear to be a very dramaticincrease, it should give us pause for thoughtbearing in mind that the mean difference intemperature between the climate in sou-thern Germany and the Mediterranean isaround 2 to 3°C.

GREENHOUSE EARTH

We have the natural greenhouse effect tothank for the pleasant global average tempe-rature of +15°C. Trace gases that occur inthe earth’s atmosphere, such as water va -pour, carbon dioxide and methane, have thesame effect as the glass panes of a conser-vatory: they allow short-wave solar radiationto penetrate and to some extent restrict thereverse emission of long-wave heat radia-tion. This is why they are called greenhousegases. Without the natural greenhouse ef -fect, average temperatures would be an in -hospitable -18°C. The carbon dioxide contentof the atmosphere, which had remained rela-tively constant at 280 ppm (parts per million)for centuries, has been rising since the dawnof the industrial era. The current concentra-tion is 390 ppm. This anthropogenic green-house effect influences both global andregional hydrological cycles.

THE KLIWA PROJECT

Are the extreme weather conditions andfloods of the last two decades harbingers ofclimate change? How will the climate andour water resources change – and how canwe respond?

The federal states of Baden-Württemberg,Bavaria and Rhineland-Palatinate are studyingthese issues in association with DeutscherWetterdienst [German Weather Service] inthe framework of the long-term cooperativeproject ‘Klimaveränderung und Konsequen -zen für die Wasserwirtschaft’ [‘ClimateChange and its Impact on Water ResourcesManagement’]. These investigations first gotunderway in early 1999.

The aim of this cross-regional interdisciplina-ry partnership project is to determine thepotential impact of climate change on thehydrology of river basins in the south ofGermany, to highlight probable consequen-ces and to propose recommendations foraction.

The first step was to analyse meteorologicaland hydrological records that cover long peri-ods of time in order to detect and evaluatetrends. This data also provided the contextfor the estimation of possible climatic condi-tions in the near future (2021-2050) based onselected regional climate projections. Theresulting climate data represents the basisfor finely meshed hydrological, or waterbalance, modelling for individual river basins.The following water management issueshave so far been studied: flooding, lowwater, groundwater, soil erosion and waterquality. The aim is to propose specific adap-tation measures in these areas.

4

KLIWA ON THE WEB

More information about theKLIWA project can be found atthe project website atwww.kliwa.de. Detailed reportsand publications about projectoutcomes and working methodsare available in the downloadarea.

Extreme weather in the summerof 2003: heatwave in CentralEurope (especially in the redareas)

5

THE EARTH`S CLIMATE 1

GLOBAL TEMPERATURES

FROM 1850 TO 2010

The diagram shows the deviationof the annual mean temperaturefrom the average temperaturebased on the long-term mean forthe period 1961 to 1990.Significant global warming becameapparent in the early years of the20th century and has speeded upconsiderably in recent decades.

Source: Met Office Hadley Centre,UK, and Climatic Research Unit,University of East Anglia, UK

THE WATER CYCLE

Two thirds of the earth’s surface iscovered with water. Part of thiswater circulates around the globein a massive cycle, in the form ofvapour, liquid or ice. Water thatevaporates from the earth’s surfa-ce rises into the atmosphere aswater vapour, condenses intoclouds and falls back to earth asrain or snow. This precipitationflows off down the earth’s streamsand rivers or infiltrates into the soiland so contributes to the forma-tion of groundwater. Most water,however, evaporates again. Thiscycle is affected by climate change.

Jahr

Tem

pera

tura

no

malie i

n °

C

The focus of KLIWA’s research: Regional climate change

Climate change is not a futuristic fantasy. Man-made climate change is already a reality – including here in our country.

Past climate trends are evaluated by studying data from the past. The range of natural variability in weather data can be

determined and trends recognised by studying time series measured over a period of several years. Data from around

400 temperature and precipitation stations in southern Germany have been evaluated as part of KLIWA with the aim of

producing a consistent database regarding future climate evolution.

IT HAS BECOME HOTTER

The mean annual temperature in southernGermany rose by between 0.9 and 1.2°C inthe period 1931-2010. The steepest rise intemperatures occurred in the 1990s. On ave-rage temperatures have increased more inthe winter months (November to April) thanin the summer months (May to October).

DREAMING OF A WHITE CHRISTMAS –

CHILDHOOD MEMORIES

Milder winters generally mean less snow.Here too a clearly distinguishable trendemerges from time series measured over anumber of years. Particularly in lower-lyingareas (up to 300 metres above sea level) andin western parts of the country, the yearsfrom 1951/52 saw a reduction of snow coverby 30 to 40 per cent, with a 10 to 20 percent reduction at intermediate altitudes. Onlyon higher ground was there actually an in -crease in snowfall in some areas. Above all,there have been fewer snow cover dayssince the beginning of the 21st century.Snow coverage is an important factor for thewater cycle and has an effect on the re -plenishment of water bodies as well as theformation of new groundwater.

DRY SUMMERS,

RAINY WINTERS

In most areas of southern Germany annualprecipitation rates remained more or lessconstant over the period under investigation.However, the seasonal distribution of pre -cipitation has changed. The winter monthshave become wetter. Precipitation in someregions has increased by up to about 30 percent. The Black Forest and areas to the northeast of Baden-Württemberg are particularly

strongly affected as is Franconia and parts ofthe Bavarian Forest as well as the Eifel andWesterwald regions of Rhineland-Palatinate.Although the summer months continue tovary over the long term, they have becomemuch drier on the whole, particularly in themonths June to August.

CYCLONIC WESTERLY: THE WEAT-

HER THAT BRINGS THE RAIN

Higher precipitation rates in winter are dueto the increase in certain large-scale weatherpatterns over Central Europe. Time seriesanalyses dating from 1881 show that therehas been an accumulation of zonal circulationpatterns in the months from December toFebruary in particular. One large-scale weat-her pattern which is especially significant forthe water management is the ‘cyclonic west-erly’, which is driven by high pressure in theAzores coupled with low pressure overIceland. This current of air extends from theAtlantic to western Europe and often bringscopious precipitation which – in combinationwith milder sea air – usually falls as rain inlowland areas. However, zonal weather pat-terns can also be responsible for violent winter storms. Sad examples are the stormLothar, which wrought devastation throug-hout western Europe in December 1999, andmore recently Kyrill and Xynthia in January2007 and February 2010, respectively.

MONITORING IN KLIWA

One major aim of KLIWA is to record variabi-lity and changes in climatological parametersand water budget components. This provi-des the data needed for further comparativeobservations. In this context a monitoringreport is published every 5 years (last upda-ted 2011) at www.kliwa.de.

6

At the top of the Zugspitze, theretreat of the glacier resultingfrom global warming is clearlyvisible.

REGIONAL

CLIMATE CHANGE 2

CHANGE IN AREAL PRECIPITA-

TION FROM 1931 TO 2010.

The diagram shows the change inareal precipitation in hydrologicalsix-monthly periods. The figuresshow clear seasonal differences: inthe summer half of the year there isno clear tendency, in contrast, therehave been general and substantialincreases in the winter months of+17 to +27% in the period 1931 to2010.

7

RISE IN AIR TEMPERATURE

FROM 1931 TO 2010

The diagram shows the change inareal mean air temperature inhydrological six-monthly periods.The rises in temperature were greater – from +1.1 to +1.4°C – inwinter than in summer – +0.6 to+1.0°C – in the period 1931 to2010.

WEATHER AND CLIMATE

WEATHER is the momentarystatus of the atmosphere,but it is also influenced bythe characteristics of theland surface.

CLIMATE, in contrast, descri-bes the weather conditionswhich prevail over mediumto large areas over longerperiods of time, usually 30years or more.

Two examples:

Thanks to the Gulf Stream, a warm ocean current, Europe has a relatively mild climate for its latitude.

Areas of snow and ice make the climate cooler, because they reflect sunlight.

Global and regional climate modelsInstruments of climate research

GLOBAL CLIMATE MODELS

Weather forecasts are often difficult. It’shappened to all of us: the weather forecastis for sun, but when the day comes for aplanned trip, you find yourself in pouring rain.With today’s resources, a reliable weatherforecast is only possible for a period of 5 to7 days at most. Producing long-term projec-tions of the way the Earth’s climate is likelyto change is an incommensurably more com-plex task, as many parameters and magnitu-des mutually influence each other and haveto be taken into account in computermodels. How all these interacting effectswork is not fully understood. Global climatemodels are based on an atmospheric modelwhich is supplemented by ocean, snow, iceand vegetation models. This means that thehuge number of calculations which arenecessary can only be made with the help ofhigh-performance computing resources.Anthropogenic influences (the ‘human fac-tor’), are taken into account in the form ofassumptions about greenhouse gas emis-sions (IPCC scenarios).

For the purposes of global climate modelling,the earth is mapped onto a grid. The compu-tational capacities of today’s computers cur-rently allow for a grid width of around 150kilometres. Given the uncertainties concer-ning the world population, economic growth,energy consumption, etc. as well as impreci-sion in the models themselves, temperatu-res and precipitation are calculated within acertain range of possible values (diagram topright). This also explains the latest figuresreleased by the Intergovernmental Panel onClimate Change that global temperaturescould rise by between 1.1 and 6.4°C by2100.

REGIONAL CLIMATE MODELS

Global climate models are far too impreciseto be used to estimate changes in regionalclimates. Regional features such as moun-tain ranges and river valleys would not betaken into account by such models. Thereare various methods available, each withtheir strengths and weaknesses, which canbe used to derive regional climate projec-tions from global climate models with thedetailed resolution that is needed.

RANGE OF REGIONAL CLIMATE

PROJECTIONS

There are several different methods availa-ble, which can be applied within a modelchain (see figure bottom right). Consideringof a number of robust climate projections(ensemble approach) produces a range ofpossible future climates, the variability anduncertainties of which can then be betterassessed. The selection of statistical regionalprojections initially used in KLIWA (WETT-REG) has recently been extended to includedynamic projections (COSMO-CLM). New climate projections which are based onenhanced climate models should also soonbe available. The extent to which the climateis changing can be determined by comparingactually recorded climate figures (for theperiod 1971-2000) with those projected forthe future. KLIWA uses the near future(2021-2050) for hydrological modelling. Atpresent the distant future (2071-2100) is con-sidered solely on the basis of changes in cli-mate figures.

8

There can no longer be any doubt that climate change is happening. One visible sign of global warming is the retreat

of many glaciers in the Alps. Not even immediate and effective climate change mitigation action will now be able to

prevent the further climate changes which are now becoming apparent: the carbon dioxide which has already been

released into the atmosphere will continue to have an effect there for several decades and so continue to exacerbate

global warming. Even if emissions of greenhouse gases could be reduced to zero – a utopian prospect in view of the

world’s insatiable energy demands – climate change would inevitably advance further. For this reason more adapta-

tion measures need to be developed.

3

9

INSTRUMENTS OF

CLIMATE RESEARCH

GLOBAL WARMING ON THE

EARTH’S SURFACE

Modelling results based on emis-sion scenarios developed in 2007by the International Panel forClimate Change (IPCC) show thepossible consequences of globalwarming for our planet.

To date the A1B (green line) emis-sion scenario has been used fordefining the possible climatic futu-re for the purpose of regionalsimulation. Scenario A1B assumesa balanced use of fossil and non-fossil energy sources in technolo-gies of the future.

(Abbildung geändert)

MODEL CHAIN FOR REGIO-

NAL CLIMATE CHANGE

STUDIES

The necessary links between themodels used to produce regionalclimate projections and simulatefuture discharge conditions areshown schematically as a modelchain.

Emission-szenario

GlobalesKlima-modell(GCM)

RegionalesKlima-modell(RCM) Dynamisch

Wasserhaus-haltsmodell

(WHM)Bias-Korrektur

Statistisch

Regionale Klimaprojektion

Abflussprojektion

10

Future simulations for our climateTomorrow’s climate

Various climatic models are available for the simulation of future conditions. The climate projections produced by such

models show a range of potentially possible temperature and precipitation values. Although the results of climate simu-

lations for different regions for 2021-2050 differ in detail, the general trend is clear: generally hotter and wetter during

the winter and drier during the summer.

RATHER HOT, AND WITH LESS ICE

The regional climate simulations for southernGermany performed in the framework of theKLIWA project show that by 2050 tempera-tures may have increased by 0.8 to 1.7°C.The annual mean increases do, however, dif-fer somewhat. Considerably warmer winterswill be accompanied by more rain and lesssnow. The results of the most recent climateprojections using a dynamic regional climatemodel are illustrated on the right. Thesesimulation results are within the range ofprevious KLIWA studies.

By comparison with today, the number ofsummer days (days over 25 °C) will increasesignificantly. The number of hot days (over30 °C) will double in almost all areas. On theother hand there will be fewer freezing days(temperature lows of 0 °C or less) and icydays (where the temperature remains belowfreezing point). For the most part resultsshow that there will be only half as many icydays. The ‘Ice Saints days’ (cold snap in earlyspring) and the last late frost will occur ear-lier – in some regions apple trees may blos-som up to two weeks earlier than at present.

WESTERLY WEATHER PATTERNS

Westerly weather patterns (especially the‘cyclonic westerlies’) are responsible for highlevels of precipitation today, and they will bean increasingly important factor in determi-ning our winter weather in the future. Thismeans an increased likelihood of floods.

INCREASING AMOUNT OF HEAVY

PRECIPITATION IN WINTER

The higher the air temperature, the higherthe evaporation rate. This in turn significantlyinfluences the hydrological cycle.

The climate simulations included in the ana-lysis show that the trend seen hitherto, withwetter winters and drier summers, will conti-nue. While in comparison with today theremay be up to 10 per cent less rain in sum-mer, in winter there will be a considerableincrease in precipitation – in some regionsup to 30 per cent. The largest amount of pre-cipitation will occur on the orographic bar-riers to the west of the regions under inve-stigation. There will also be considerablymore winter days with heavy precipitation(25 mm or more); in some regions the num-ber of such days will double. At the sametime, there will be more days on which itdoes not rain at all and dry periods will lastlonger in summer. In the distant future (up tothe year 2100) most climate projectionsshow a fall in mean annual precipitation.

TO SUM UP: THE TREND IS SET TO

CONTINUE:

It will become generally hotter, both in summer and winter.Summers will be somewhat drier, wintersa good deal wetter.Westerly weather patterns will increase, with a tendency to higher levels of pre-cipitation. Dry weather will become more prevalent in summer.

As a result of climate change,apple trees will blossom up totwo weeks earlier in someregions.

11

TOMORROW’S

CLIMATE 4

RISE IN AIR TEMPERATURE

UP TO 2050

The diagram shows the change inareal mean air temperature in theperiod 2021-2050 compared with1971-2000. The figures are exam-ples of results from the CCLMVersion 4.8 regional climate projec-tion for the hydrological six-monthperiods. Temperatures continue torise, whereby the change in tem-perature in winter is, at approxima-tely +0.9°C, somewhat smallerthan the change in summer tem-perature (approximately +1.2°C).

CHANGE IN AREAL PRECIPI-

TATION UP TO 2050

The diagram shows the change inareal precipitation in the period2021-2050 compared with 1971-2000. The figures are examples ofresults from the regional climateprojection CCLM Version 4.8 forthe hydrological six-month periods.The scale of the changes differsaccording to the season. The figu-res show substantial increases inwinter of up to +15% and modera-te reductions in summer of up to -6%.

ON A FINE SCALE – THE WATER

BALANCE MODEL TOOLBOX

Water budgeting models are currently thefavoured means of quantifying the impact ofclimate change on runoff. Quantification ofthe anticipated changes is a prerequisite forthe conception and evaluation of adaptationmeasures. Water balance models serve tocalculate the spatial and temporal distributionof essential components of the water cycle –such as precipitation, evaporation, infiltration,water storage and runoff. They help us toshow and assess the effects of changes onthe entire system that the water cycle repre-sents.

Water balance models use a fine grid (dia-gram top right) to, amongst other things,describe the following hydrological pro -cesses: evaporation, snow accumulation,compaction and melting, soil water storage,flow patterns in bodies of water and re -tention of water in lakes.

Uncertainties in individual models in the global model > regional model > waterbalance model chain ultimately produce arange of potential changes.

Possible applications of water balancemodels:

Estimate of the effects of environmental change, especially climate change or changes in land use, on the water cycle, with implications for runoff, infiltration andevaporation.

Continuous runoff predictions for low water, medium water levels and flooding as a basis for operations – e.g. so as to improve low water management and flood precautions (flood predictions and early warning systems).Regional hydrological studies for river basins, in accordance with the re -quirements of the EC Water Framework Directive.Provision of hydrological input variables for water quality and groundwater models(with implications for the heat and oxygen budget, groundwater flow and transport, etc.).

RIVER BASINS IN GRID FORMAT

Water balance models on a 1 x 1 km gridhave been set up for KLIWA’s river basins to estimate the effect of climate change on the water cycle. For KLIWA, the initial aim of the modelling was to investigate theexpected climate-induced increased dangerof flooding.

Today the emphasis is on the investigation oflow water conditions. For this purpose thedaily runoff from KLIWA’s river basins, pre-sent and future, is being computed (diagrambottom right). This approach is supplemen-ted by special soil water models that serveto determine the rate of groundwater re -plenishment.

12

Runoff simulation toolsWater balance models

Global and regional climate projections do not provide enough information on their own about the impact of global

warming on water resources management. This means that it is only possible to determine runoff changes, especial-

ly the accentuation of floodwater runoff or changes in low water runoff, resulting from climate change in southern

Germany if the results of regional climate models are ‘fed into’ water budgeting models that have a high degree of

resolution.

With increasingly mild winters,there is a greater danger of flood ing in the south ofGermany, especially in the winter months.

WATER BUDGETING MODELS 5

13

FINDINGS FROM WATER

BUDGETING MODELLING

Comparison of a measured timeseries for river discharge withsimulated data calculated using awater balance model, for a selec-ted gauging station for the year1984.

Höhenmodell30 x 30 m

Landnutzung30 x 30 m

Bodeneigenschaften

Flussnetz

Vernetzung der Rasterflächen

DATA BASIS FOR WATER

BALANCE MODELS

Water balance models (WBMs)are created using extensive digitaldata records (e.g. digital elevationmodels, satellite classification ofland use, soil properties and riveri-ne networks). For each separateWBM grid square, up to 16 diffe-rent land uses are computed,each with its specific evaporationand runoff characteristics.

14

Our most important drinking water reservoirGroundwater

In the south of Germany about 80 per cent of our drinking water comes from subterranean groundwater reserves. The

impact of climate change on groundwater resources is therefore an especially important water management issue. It

is essential that supplies of drinking water are secured for the future despite changing climatic conditions.

FIRST CHANGES OBSERVED IN

MEASUREMENT DATA

Groundwater levels and the discharge fromsprings have been under observation forseveral decades already – in some cases,readings go back over a century. Serial dataobtained at observation points yield informa-tion about the long-term development ofgroundwater reserves and spring discharge.Systematic evaluation of selected timeseries for the most important groundwateraquifers in Baden-Württemberg, Bavaria andRhineland-Palatinate shows that changes inannual patterns have already taken place inmany cases. For example, the annual maxi-mum of the groundwater level now occursearlier in the year than indicated by the histo-ric record mentioned above– this is a directconsequence of changes in annual tempera-ture patterns and precipitation levels. Inmany cases, there is also an increase in therange between minimum and maximumvalues for the year.

GROUNDWATER RECHARGING

Changes in the annual distribution of precipi-tation – with less rain in summer and higherprecipitation in the winter months – will havesignificant effects on the soil moisture regi-me. In summer there will be less infiltratingwater, in winter there will be more than inthe past. Accordingly, in the future, there willbe less water available in the soil during thevegetation period (top right). This is reflectedin an increase in the drought index for thethree federal states of almost 14 days peryear in the period 2021-2050. Baden-Württemberg and Bavaria currentlyhave an annual mean groundwater rechargeof just over 200 mm, Rhineland-Palatinate of

100 mm. For comparison: Mean total precipi-tation in Baden-Württemberg is around 960mm, in Bavaria about 930 mm and inRhineland-Palatinate 780 mm. In contrast tothe drought index, the average annualgroundwater recharge for the period 2021-2050 is not expected to change substantially.The soil moisture regime calculated on basisof the WETTREG 2006 (ECHAM5/A1B) cli-mate scenario produce a slight increase ingroundwater recharge in Rhineland-Palatinate of up to 15 mm/a, whereas inBaden-Württemberg and Bavaria there willbe reductions of up to 30 mm/a.

RECOMMENDATIONS FOR ACTION

The basis for sustainable groundwatermanagement is the regular observation ofgroundwater quantity and quality. It is essen-tial, therefore, that the observation networkis consistently maintained to monitor theimpact of climate change. Even today, exten-ded droughts in summer may result in spati-ally and temporally restricted water shorta-ges. Efforts to avoid potential water shorta-ges will need to include regional and super-regional networking solutions to strengthenthe resilience of the water-supply infrastruc-ture. More efficient methods of calculatingirrigation requirements are also needed foragricultural use. As well as extended periodsof drought in summer, we can also expect tosee longer periods with heavy precipitationin the future, especially during the winter.This may lead to higher groundwater levelslocally. This must be taken into accountwhen planning development areas, particu-larly when water saturation represents apotential hazard.

Springs are bubbling, andgroundwater reserves are stillbeing generously replenished.

15

GROUNDWATER 6

MEAN ANNUAL GROUND-

WATER RECHARGE FROM

PRECIPITATION TODAY

(1971-2000)

Groundwater recharge is ofutmost importance for watermanagement and is an impor-tant measure of the naturalregenerative capacity of ground-water resources. In KLIWA, theformation of new groundwaterin the period 1971-2000 wascalculated for the investigationarea using a soil water model.

MEAN ANNUAL DROUGHT

INDEX TODAY (1971-2000)

In KLIWA, the drought index forthe period 1971 to 2000 was cal-culated for the investigation areawith a soil water model. Thedrought index describes theduration of periods in which soilwater content is less than 30%of the storage capacity. No infil-tration takes place during thisperiod and vegetation suffersfrom excessively dry conditions.

More frequent and longer lasting drought Low water

The drier and hotter summers to be expected in future will mean lower water levels. These low water phases will

not only mean difficulties for inland waterway shipping, but will also bring problems for agriculture, the energy

industry and the supply of drinking water. The economic consequences are potentially severe: The persistent drought

period in 2003, for example, inflicted higher economic costs on Germany than recent catastrophic floods along the

Rhine, Oder and Elbe. Drought conditions not only affect water management, they also impinge on flora and fauna

and have an extensive impact on low water levels.

FALLING WATER LEVELS DESPITE

EXTREME WEATHER CONDITIONS

Climate change and global warming lead toan intensification of hydrological cycles andto more frequent extreme weather events.These changes must be reflected in the way water resources are managed: droughtperiods (such as the hot summer of 2003,when streams and small rivers dried up,inland waterway shipping ground to a halt in some places and groundwater levels dropped severely) are accompanied byfloods caused by persistent heavy rain.

LESS RAIN AND MORE EVAPORA-

TION = LESS RUNOFF IN SUMMER

Climate models predict increased precipita-tion during the winter and lower precipitationin the summer – the precipitation regimethroughout the year is undergoing a processof change. At the same time, evaporationwill increase as a result of the higher air tem-perature. The likelihood of serious droughtoccurring in southern Germany, for example,has increased significantly since 1985.

Available runoff simulations show a signifi-cant decrease in mean monthly low waterdischarge from June to November in theriver basins studied in southern Germany.The medium decrease in many catchmentsis greater than 10 per cent. The only area inwhich an increase in runoff is found is in thecatchment area of the Nahe (Rhineland-Palatinate). Nonetheless, there is a clear andgeneral tendency towards lower runoff(above right). The sharpest decline is likely tobe found in the autumn months fromSeptember to November. With 21 per centless low water discharge in the month of

September, the decline is most marked inthe tributaries to the Rhine in the southeastand southwest of Baden-Württemberg (dia-gram bottom right). The annual low waterdischarges for the Rhine River itself tend tobe higher in the future scenario. This meansthat, as things currently stand, no increase inmean low water discharges is expected fromthe water level of the Rhine up until 2050.The next step is to investigate extreme lowwater discharges. In most regions low waterperiods will last longer; south of a line drawnbetween Karlsruhe and Coburg up to 50 percent longer and to the north of this line(including the Nahe catchment area) 25 to 50per cent longer. Experts believe that the rea-son lies in the greater frequency of largescale dry weather systems over wide geo-graphical areas.

WORST CASE NOT COVERED

The runoff simulations show that low waterconditions are strongly influenced by futurechanges in mean air temperatures and preci-pitation. Regional climate projections may,however, vary widely (between 1.0 and1.8°C) depending on the emission scenarioand climate model used. Low water dischar-ges and periods could therefore actually turnout very much worse than predicted. One ofKLIWA’s tasks is therefore to estimate futurelow water developments and to produceappropriate proposals for adaptation mea -sures.

16

Long periods of drought desic-cate the soil and mean loss ofharvests.

LOW WATER 7

17

FUTURE CHANGES IN LOW

WATER DISCHARGES

DURING THE SUMMER

The two maps show the geogra-phical distribution of the anticipa-ted changes in mean low waterdischarge (MNQ/MLQ) for thesummer period of June toNovember, derived from themonthly low water dischargelevels for the river basins underinvestigation. The various coloursillustrate the percentage change inthe period 2021-2050 comparedwith 1971-2000. The results arefrom two different climate pro -jections: the results for the mapon the ‘left’ are based on theWETTREG 2006 model and thosefor the map on the ‘right’ on theWETTREG 2010 model forBavaria.

ANNUAL PATTERNS OF LOW

WATER DISCHARGE

The diagram shows the changes inmean monthly low water dischargein various river catchments as wellas the mean value for all gaugingstations included in the study andthe minimum and maximum chan-ges calculated. The diagram showsthe percentage change in themonthly mean values in the period2021-2050 compared with the period 1971-2000. The results arebased on the WETTREG 2006 climate projection.

Klimaprojektion

WETTREG 2010

Klimaprojektion

WETTREG 2006

„Flexible and no regret“strategyFlooding

Even if the chain leading from the global model to the regional model and thence to the water balance model is subject

to uncertainty, the findings nonetheless indicate that we can expect to see more flood events in future. A flood response

strategy has therefore been developed as a precautionary measure. In this context adaptation does not mean building

new metre-high river embankments everywhere. Instead measures need to be developed which mitigate the expected

impact of climate change – measures that will be effective in the long term and that can be modified at relatively low

cost. Flood prevention measures have a particularly important part to play in this respect.

THE CLIMATE CHANGE FACTOR

The planning of flood protection facilities isgenerally based on the HQ100 value. HQ100is the flood discharge which statistically spea-king will be exceeded just once in 100 years.This means that embankments constructedin accordance with this value should be ableto cope with a ‘flood of the century’.Simulations based on water balance modelsfor the river basins of Baden-Württembergand Bavaria show that flood discharge levelsare likely to increase almost universally, espe-cially in winter. For this reason both federalstates have decided – as a precautionarymeasure - that plans for new flood protectionfacilities must include a climate change factorto take into account the effects of climatechange. The simulation for the Neckar, forexample, is based on a discharge for a 100-year flood (HQ100) which will rise by 15 percent between now and 2050. This meansthat the HQ100 value must now be multipliedby a climate change factor of 1.15 – in otherwords, the flood protection systems must infuture be designed to cope with a 15 percent higher discharge than today’s valuesindicate, or at least planned in such a waythat they can be adapted to meet heightenedrequirements.

DIFFERENT CLIMATIC CONSEQUEN-

CES AND CLIMATE CHANGE FAC-

TORS

All the river catchments in Baden-Württem -berg have now been very carefully scrutini-sed. Regional climate change differenceshave consequences in terms of expectedflood discharges (see image top right). A cli-mate change factor of 1.25 has been deter-

mined for the Upper Danube area, for exam-ple. Smaller floods, and floods of moderateseverity, can also be expected to increase.The HQ5 discharge for a flood on the UpperDanube – which today can be expected tooccur on average every five years – has goneup by 67 per cent. This means that, in thefuture, the current HQ5 value for the UpperDanube will have to be multiplied by a clima-te change factor of 1.67. The HQ5 climatechange factor for the area around the tributa-ries to the Upper Rhine is 1.45, for example.The factor is lowest (1.24) in the UpperSwabia / Lake Constance region.

A climate change factor has also been intro-duced in Bavaria based on the earlier WETT-REG 2003 study findings – here the statisti-cal value of HQ100 is increased by 15 percent right across the board. On this basis theexpected effects of climate change are alrea-dy being taken into account in the planningof new flood protection measures. The fun-damental data underlying the climate changefactor are still subject to refinement and furt-her research. This may lead to regional finetuning in future.

In Rhineland-Palatinate flood protection mea-sures are always planned according to theactual peripheral conditions which apply ineach individual case, with a particular focuson the threat to the population, the potentialdamage caused by flooding and considera-tions of economic viability. The studies forthe ‘special case of the Upper Rhine’ will befollowed up by runoff studies for the wholeof Rhineland-Palatinate and the Middle Rhinewhich should show whether further adapta-tion measures are required in Rhineland-Palatinate.

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FLOOD PROTECTION –

WHAT DOES IT MEAN IN

PRACTICE?

Example, flood embank-

ment:

The embankment is built asoriginally planned, but a stripon the outside is left clear toallow the dam to be broade-ned and raised in the future ifnecessary.

Example, bridge:

The regional climate factorwill be taken into account inthe planning of a bridge fromthe very start as subsequentadaptation is often impossi-ble for technical reasons.

Example, retaining wall:

The statics of a new retainingwall have been designed insuch a way that there will beno difficulty if additionalheight is needed in future.

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FLOODING 8

KLIMAANDERUNGSFAKTOREN IN BADEN-WURTTEMBERG

Klimaänderungsfaktoren f(T,K)

1 2 3 4 5

2 1,25 1,50 1,75 1,50 1,75

5 1,24 1,45 1,65 1,45 1,67

10 1,23 1,40 1,55 1,43 1,60

20 1,21 1,33 1,42 1,40 1,50

50 1,18 1,23 1,25 1,31 1,35

100 1,15 1,15 1,15 1,25 1,25

200 1,12 1,08 1,07 1,18 1,15

500 1,06 1,03 1,00 1,08 1,05

1000 1,00 1,00 1,00 1,00 1,00

Bemerkung: Für Jährlichkeiten T>1000 a ist der Faktor gleich 1,0

THE SPECIAL CASE OF THE UPPER RHINE

Owing to the special situation for the Rhine, such as incomingrunoff from Switzerland and water regulation measures along theriver’s upper reaches, the stretch of the Rhine from Freiburg toMainz was not included in the first runoff studies performed aspart of KLIWA. Robust climate projections are now available forthe entire Rhine catchment area – including Switzerland – as wellas suitable water budgeting/balance models which cover theretention effect of Lake Constance, the large lakes on the edge ofthe Alps and the entire Rhine catchment area up to Worms(watershed area of approximately 69,000 km²).The flow of water down the Rhine as far as Worms is influencedparticularly strongly by the runoff in the Swiss Alps as well as theseasonal cycle of snow build up and thawing. As a result the lar-

gest volumes of water occur in the hydrological summer half-yearfrom May to October.Initial analyses of relative changes between the future scenario2021-2050 and the current status 1971-2000 for the water level ofthe Rhine show that no substantial changes are expected formean flood flows. With the exceptions of the months of May andOctober, results even show a slight decrease in mean flood flowvolumes for the summer half-year, during which the highestdischarges occur. In the winter from November to April increasesof less than 10% are simulated. This means that, as things cur-rently stand, no increases in mean flood flows are expected forthe water level of the Rhine up to 2050. The next step is to exa-mine potential changes in extreme flood flows.

CLIMATE CHANGE MARKUP

In planning the dimensions of flood protection facilities, a markupon the current value for flood discharge takes account of the possi-ble effects of climate change. The freeboard margin serves to pre-vent breaching of flood protection barriers (e.g. as a result of higherwater levels caused by waves and wind).

T (Jahre)

20

When it rains it pours Heavy rainfall

Rising temperatures and increasing evaporation are accentuating the atmospheric hydrological cycle. As a result,

more frequent heavy rainfall may be anticipated. Intense localised rainfall events are more and more frequently excee-

ding the capacity of drainage systems in built-up areas. They also lead to more intensive soil erosion on unprotected

farmland. Owing to the lack of available measurements, these changes can currently only be estimated by modelling.

URBAN DRAINAGE

Rain water which does not seep into the soilor flow into surface waters in the vicinity of abuilt-up area is directed into drainagesystems installed in developed areas. Urbandrainage problems occur when very heavyprecipitation events or sudden downpourspose a threat of flooding. The evidence isthat such events are occurring more fre-quently and more intensively at the regionallevel. There are, however, no long-term andrepresentative all-encompassing records.

However, using the extended simulationmethod which is applied as standard in plan-ning practice it is possible to produce veryprecise statements about the way canalsystems will cope under future climate con-ditions. Artificial precipitation patterns arerequired for this purpose and can be genera-ted with the NiedSim computer programmewhich is used by KLIWA partners.

The latest version of NiedSim-Klima takesaccount of the most recently available fin-dings from climate research. This means thatprecipitation patterns can be produced whichare representative for climate conditions forany number of years up to 2050. New fin-dings will be integrated in NiedSim-Klima assoon as they are produced by climate re -search.

Local authorities are already carrying outcomparative studies on the performance oftheir drainage systems in the years 2010,2030 and 2050. In addition, fundamentalinvestigations should also be undertaken toproduce general statements about the antici-pated impact of climate change on watermanagement in built-up areas.

LOSING THE GROUND UNDER OUR

FEET

One-off, intensive precipitation, such as athunderstorm, can not only flood cellars andstreets, but can also cause huge erosiondamage to unprotected fallow land or vege-tation-free land. This not only results in theloss of fertile soil, damage also extendsbeyond the actual eroded area to causemuddied paths and streets. Bearing this inmind, one KLIWA subproject focuses on thefuture risk of erosion due to heavy rainfall.

CLIMATE AND EROSION MODEL-

LING

In order to estimate the future risk of erosiona regional climate model is linked up to a soilerosion model. The precipitation data at veryhigh temporal and spatial resolutions whichare needed for this purpose are delivered bythe COSMO-CLM regional climate model. A‘nesting’ procedure involves using lowerresolution model data as the boundary condi-tion for the higher resolution of the regionalclimate model. This means that single burstsof heavy precipitation can be simulated at atarget resolution of 1 x 1 km and 15 minu-tes. These precipitation records are thenused as input parameters for the LISEM(Limburg Soil Erosion Model) physical ero-sion model which is used to calculate theamount of soil erosion and water dischargein selected, erosion prone areas.

Durch Starkregen überlastete Kanali-sation (Quelle: itwh)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

0,10

32 mm/h 37 mm/h

0,05

27 mm/h

0,22

43 mm/h

2,20

48 mm/h

3,85

Niederschlagsintensität (mm/h)

Bo

den

ab

trag

(t/

ha)

0

10

20

30

40

50

60

70

80

90

100

0 6 12 18 24 30 36 42 48 54 60 120

5102050100

Zeit (min)

Nie

ders

ch

lag

sin

ten

sit

ät

(mm

/h)

21

HEAVY RAINFALL 9

SOIL EROSION MODELLED

WITH LISEM USING

KOSTRA DATA IN A TYPI-

CAL LOESS SOIL AREA

The illustration clearly showsthat at a precipitation intensity of37 mm/h and higher, the amountof soil erosion increases sharply.Although precipitation intensityonly increases by 16% to 43mm/h, soil erosion increases tenfold. The KLIWA subprojectwill look more closely at theextent to which there will be anincrease in critical heavy rainfallin the future.

ONE-HOUR STAGE PRE -

CIPITATION HYDROGRAPH

FOR DIFFERENT RETURN

PERIODS (5 TO 100 YEARS)

In addition to the input parame-ters for relief, soils and vegeta-tion, the LISEM erosion modelalso requires data for precipita-tion duration and intensity. TheKOSTRA Atlas (DWD, 2005) isused to generate precipitationhydrographs which then provideinput parameters for LISEM. Thisenables studies to be made ofthe precipitation intensity atwhich the amount of soil erosionsignificantly increases.

22

Impact on water qualityAquatic ecosystems

Climate change affects inland waters and the animal and plant life in and around them. Rising temperatures and fal-

ling runoff or water levels have a negative impact on the oxygen balance and change the composition of biotic com-

munities. This could have an enduringly negative impact on the good status of our waters. But what has actually

changed and what changes can we expect in the future? The complex and multilayered interactions between water

characteristics and ecological systems as well as the relative paucity of relevant data make it very difficult to answer

this question.

GETTING INTO WARMER WATER

If the air gets warmer, so will streams, riversand lakes. Changes in precipitation will resultin different levels of runoff. However, it isnot only freshwater ecology which will haveto adjust. The many diverse and extensivewater uses will also be affected. The waterused as coolant in power stations will be -come too warm, for example, and will nolonger serve its purpose as efficiently.

MULTIPLE INFLUENCES ON WATER

ECOLOGY

Climate change will impact fundamental factors in streams, rivers and lakes, such aswater temperature, discharge conditions, thebuild up of fine sediments or the concentra-tion of nutrients. This sets off a chain ofevents which ultimately impacts aquatic floraand fauna: some species become increasin-gly rare or disappear altogether, while othersbecome invasive. Biotic communities andthe functionality of aquatic ecosystemschange. While it is already possible to modelthe impact of climate change on waterresources in southern Germany comprehen-sively, for the whole region, changes inwater ecology have only been studied insmaller areas to date. There is evidence, forexample, that biotic communities may betending to move upstream in rivers and stre-ams water. A literature study commissioned by KLIWA,which focuses on rivers and streams in southern Germany, uses causal chain ana -lysis to illustrate the impact of climate chan-ge on water quality at the regional scale forthe three federal states of Bavaria, Baden-Württemberg and Rhineland-Palatinate. Thestudy, with its extensive literature and sensi-

tivity analysis, demonstrates that changes inthe water quality of rivers and streams maybe expected in many areas in the future, butat the same time also reveals many areas inwhich there are still significant knowledgegaps.

INTO THE FUTURE WITH MONITO-

RING

It is not as yet possible to say just what in -fluence climate change will have on the qua-lity of our inland waters. In order to obtainrobust data in this field, the latest monitoringreport on flowing waters will be reviewedand appropriate evaluation procedures andmethods developed. What are the most important indicators?How often and for which water bodies willthey have to be determined? The answers tothese questions will provide a basis onwhich to address many issues in the futureand to find and define appropriate adaptationmeasures.

INVASIVE SPECIES – BENEFICIARIES

OF CLIMATE CHANGE?

Invasive species are flora or fauna whichhave migrated into a particular habitat owingto the direct or indirect influence of humanbeings. Many new species have appeared inGermany in the last two decades in particu-lar. This phenomenon is mainly ascribable tothe connections between rivers systems cre-ated by navigable channels. Many invasivespecies can tolerate changes in temperature,eutrophication as well as salination and the-refore benefit indirectly from global warming.Thirty of these species are described indetail in a KLIWA study.

TAPE GRASS

Tape or eel grass (Vallisneria spi-ralis) is an invasive aquariumplant in southern Germany whichoriginates in tropical and sub-tro-pical regions. It is regarded as apotential beneficiary of globalwarming. Large stands of tapegrass have now formed on theMosel and are displacing nativebur reed in some places.

KLIWA study www.fliessgewaesserbiologie.de

23

AQUATIC ECOSYSTEMS 10

COMPLEX ECOSYSTEMS

Global warming is raising thetemperature of water in cool stre-ams and altering seasonaldischarge patterns. Altered snowcover, increased heavy rainfall orlong periods of drought duringthe summer are even in the pro-cess of changing the very natureof river beds and microhabitats.This can seriously disturb ecosy-stems in streams.

KLIWA initially focussed on the problems presented by flood hazards and has elaborated concrete measuresfor dealing with these. Studies of the impacts on runoff in the Rhine and Danube are currently underway. Themain emphasis of the investigations has now also shifted to the effects of climate change on low waterdischarge and the status of groundwater. Changes to the water cycle have direct consequences for the use ofour water resources – whether as directly tapped for drinking water and agricultural irrigation, for use as a coo-lant in power stations or as a transport route for shipping. This is linked to the question of the effects of clima-te change on the quality and ecological status of our waters - currently a principal area of interest for the workin progress.

The focus will also be on the anticipated increase in heavy precipitation (thunderstorms). This heavy rainfallcan cause local flooding or serious damage to agriculture as a result of soil erosion and implies additional chal-lenges for the protection of the soil. This presents increasing problems for municipal drainage networks. Asestimates of the consequences of climate change are based on data determined by means of climate models,it is essential to go on refining these models so as to minimise the factor of uncertainty. This is another areawhere KLIWA will be able to make its contribution.

Regional measures that seek to cushion the effects of climate change are one thing – but even more impor-tant are steps dedicated to active climate protection. The reduction of greenhouse gas emissions must be atop priority here. The delayed response of the climate system means that even if emissions were to come toan immediate stop (a purely fictitious scenario), temperatures would still go on rising in the immediate future.Therefore each and every one of us must do what we can – otherwise future generations will be confrontedwith even more serious problems.

Climate change is the biggest challenge facing humanity today – and it affects us all.

Future prospects / OutlookIn the future we can expect hotter/warmer and drier summers as well as milder and wetter winters. The

change in the distribution of precipitation will have corresponding effects on the regional water cycle

and, as a result, on the water balance of our river basins.

Klimawandel Abiotische Veränderungen

Biologische Veränderungen

Lufttemperatur

Niederschlag:ExtremeSaisonalität

FeinsedimenteintragWasserhaushalt

MikrohabitateWassertemperatur

SauerstoffSchneeverhältnisse

Beschattung/Randstreifen

Makrozoobenthos

Fische

Wasserpflanzen