Climate Change in Southern Germany
Challenges – Adaptation

CONSEQUENCES FOR
WATER MANAGEMENT

Bayerisches Staatsministerium fürUmwelt und Verbraucherschutz

MINISTERIUM FÜR UMWELT,ENERGIE, ERNÄHRUNG
UND FORSTENKLIWA STANDS FOR CLIMATE CHANGE AND CONSEQUENCES FOR WATER MANAGEMENTKLIWA IS A COOPERATION PROJECT BETWEEN THE GERMAN STATES OF BADEN-WÜRTTEMBERG, BAVARIA
AND RHINELAND-PALATINATE AND THE DEUTSCHER WETTERDIENSTCONTE N T S

1		 T HE C H A L L E NGE OF C L IMA T E CH A NGE

4FOREWORD

2		 R E G I O NA L CH A NGE S

6

3		 I N S T R UME NT S OF CL IM A T E RE S EA R C H

84		 ADAP T A T ION ST R A T E GIE S

105		 G R O U ND W A T E R

12Water is one of the most valuable gifts of nature. We all live from and withwater. Water managers bear a heavy responsibility for the sustainability of a
resource which is vital for life as well as for protecting against the dangers it canpose. Water management standards in Germany are very high. Wherever necessary we protect and improve the status of water. We have sufficient drinking
water of good quality and we invest millions of euros in improving flood protection and low-water management.

6 		 LO W W A T E R

147		 FLO O DING

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8 		 HE AVY RA INF A L L

189 		 AQ U AT IC E COS YS T E MS

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10 W AT E R T E M P E R A T UR E / OUT L OOK

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Bayerisches Staatsministerium fürUmwelt und Verbraucherschutz

MINISTERIUM FÜR UMWELT,ENERGIE, ERNÄHRUNG
UND FORSTEN

But the water cycle is changing. Climate change also alters the water budget inGermany. Today we know that the Earth‘s mean temperature has already risen
significantly worldwide and will continue to increase as a result of the greenhouse effect. Mankind will no longer be able to stop this process. At best they
may be able to slow it down. We must all do our part in acting consistently andeffectively to mitigate climate change.
In consequence of climate change and its regional impacts we must be prepared
for an increase in extreme weather events. There will almost certainly be more
intense rainfall events, heat waves and dry periods in the future. This means thatthose responsible for managing water need to evaluate the potential impacts andto develop strategies and ways of adapting locally to these changes.
The studies performed up to now within the „Climate Change andConsequences for Water Management“ (KLIWA) cooperation give us a good ideaof how climate change will impact flooding, low-water events or water tables
here in southern Germany. These evaluations are all subject to a high degree of
uncertainty. The great challenge will be to assess the impact of climate change
accurately and to set the right course for the future. A great deal of fundamental
work remains to be done. How can uncertainties concerning future developments be characterised and communicated to the public? What impact will climate change have on the water quality of our streams and rivers? What adaptation
measures does the precautionary principle require now and in the future?
We can mitigate the impacts of climate change by taking consistent action at the
global, national and regional levels. Greenhouse gas emissions must be reduced
as far as possible. However, there will be irreversible consequences that will
necessitate adaptation measures. This means that climate-sensitive systems
have to be prepared as well as possible for the changes ahead. This can beensured by enhancing and reducing the vulnerability of systems. Ongoing work isneeded to develop the climate change knowledge base. The KLIWA cooperation
provides an important contribution to the field of sustainable water management.

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3THE C HAL L EN G E O F
C L I MATE C HAN G E

1Where do we stand?
The challenge of climate change
The International Climate Treaty negotiated at the World Climate Conference in Paris in December 2015 came into
effect on 4 November 2016. The Paris Agreement commits the international community to limiting global warming
to well below 2°C and, if possible, to below 1.5°C. This is an ambitious target and calls for huge efforts to avoid
greenhouse-gas emissions.
CLIMATE CHANGE IS HAPPENING
NOW

2014 was the warmest year inGermany since the beginning ofrecording. Except of August, average temperatures were significantly
higher in every month of 2014 thanin the 1961–1990 international reference period.
© DWD: Elke Rosskamp.

The Earth‘s climate has varied naturally overmillions of years. At times Europe enjoyed atropical climate, at others the continent wascovered by massive ice sheets. Sediment
drill samples and pollen analyses yieldinsights into climate fluctuations during the
Earth‘s early history. Weather data havebeen collected on a regular basis since1860. Evaluations of these data show that,over the last 155 years, the mean global
temperature has risen by around 1°C, andin Germany it has risen by as much as
1.3°C since 1881. Extreme weather events
have occurred in recent years: the severe
flooding of 2013, the extremely dry summerof 2015 and the flash floods of spring 2016.
Coincidence or climate change? Anyway,
adaptation to current climate change and,as far as possible, precautionary measuresagainst extreme weather events are
essential.

KLIWA ON THE WEB
GREENHOUSE EARTH
More information about KLIWA
can be found at the project website at www.kliwa.de. Detailed
reports on project outcomes andworking methods are available
in the download area ("publications").

4

We have to thank the natural greenhouseeffect for the pleasant global average temperature of +15°C. Trace gases that occur
in the Earth’s atmosphere, such as water
vapour, carbon dioxide and methane, havethe same effect as the glass panes of a conservatory: they allow short-wave solar radiation to penetrate and to some extent restrict
the reverse emission of long-wave heat radiation. This is why they are called greenhousegases. Without the natural greenhouseeffect, average temperatures would be an
inhospitable -18°C. The carbon dioxide content of the atmosphere, which had remained
relatively constant at 280 ppm (parts per
million) for centuries, has been rising since
the dawn of the industrial era. The current
concentration is 405 ppm. This additional

anthropogenic greenhouse effect influences
both global and regional hydrological cycles.
This calls for regional adaptation measures.
THE KLIWA COOPERATION
Are the extreme weather conditions andfloods in southern Germany in recent
decades unmistakable harbingers of climate change? How will regional climateschange and what effect will those changes
have on one of our most important resources: water? How should we respond? To
address those issues, the federal states ofBaden-Württemberg, Bavaria and RhinelandPalatinate launched the KLIWA cooperationin association with Deutscher Wetterdienst
in 1999. The aim of this interstate and interdisciplinary partnership project is to determine the potential impact of climate change on
the water budget and ecology of river basins
in southern Germany and to derive recommendations for action.
Long-term observations of meteorologial andhydrological data are prerequisite for studies
on climate change - the longer the better.
Such data show how the climate has changed over time and are used with selected
regional climate projections to estimate climatic conditions in the future. These climate
data are used to simulate the future water
budgets of river basins. The KLIWA studies
undertaken to date have considered the issues of flooding, low water, groundwater, soil
erosion and water ecology. Specific adaptation measures are based on the changes
which are detected.

TEMPERATURE CURVE INGERMANY FROM 1881 TO
2015
The diagram shows the deviationof the annual mean temperaturefrom the average temperature
based on the long-term mean
for the period 1961 to 1990.
The 1961-1990 mean is shownin green and the linear trend forthe complete series in black. The
figures show that the pace of
global warming has accelerated
significantly in recent decades.
The ten highest mean temperatures since nationwide records
started in 1881 are shown in
red (the same mean value canappear several times). There has
been a significant increase in theincidence of warm years in the
21st century.

THE WATER CYCLE
Two thirds of the Earth‘s surface is covered with water. Partof this water circulates aroundthe globe in a massive cycle,
in the form of vapour, liquid or
ice. Water evaporating from the
Earth‘s surface rises into theatmosphere as water vapour,condenses into clouds and fallsback to Earth as rain or snow.
This precipitation flows off down
the earth’s streams and rivers
or infiltrates into the soil and socontributes to the formation ofgroundwater. Most water, however, evaporates again. This cycle
is affected by climate change.

5

R EG I O N AL
C HAN G ES

2Climate monitoring in KLIWA
Regional changes
Climate change up to now is evaluated by first studying the available data for the past. The range of naturalvariability in weather data can be determined and trends can be identified from these long-term data series. Data fromaround 200 temperature and 900 precipitation stations in southern Germany have been evaluated and regionally standardised for KLIWA to produce a robust database for future climate trends.

IT HAS BECOME HOTTER

Glacier recession will have a huge
impact on the water budget.
© fotolia.com

The global warming trend is also evident insouthern Germany. The mean temperature in
the KLIWA federal states of Bavaria, BadenWürttemberg and Rhineland-Palatinate roseby an average of 1.3°C between 1931 and2015. In a total of 14 of the 15 years since2001 temperatures have been higher thanthe long-term mean temperature for theperiod 1961-1990. With mean temperaturesapproximately +2°C above the long-term
mean, 2014 has so far been the hottest year
since records began in 1881. This meansthat the warming trend has accelerated evenfurther. Since 1931 overall temperatures
have increased more in the winter months
from November to April than in the summer
months from May to October. Over the last
15 years, however, most of this further warming has occurred in the summer.

MORE EXTREME PRECIPITATION IN
WINTERKLIWA also measures trends for maximum
daily extreme precipitation. However, because extreme precipitation tends to be a local
phenomenon, these trends are naturally lessuniform than for areal precipitation. Still, in
the hydrological winter half-year from May
to October, there are clear positive regional
trends (up to +33% from 1931 to 2015)
throughout southern Germany; which is aprecondition for an increase in winter flood
situations. There is as yet no clear discernible trend for the summer half-year. Currently
it is difficult to reach conclusions on longterm trends for events of less than one day‘s
duration due to the lack of long-term records
and high-resolution measuring networks.
It may be possible to obtain information
about precipitation from other sources in the
future, such as radar measurements.

DRY SUMMERS, RAINY WINTERSMONITORING IN KLIWA
In most areas of southern Germany annual
precipitation rates remained more or lessconstant over the investigation period.
However, the seasonal distribution of precipitation has changed. The winter months havebecome wetter. Between 1931 and 2015,
precipitation increased by 16%-27% in someregions. Those changes have been most pronounced in the Black Forest and areas to thenorth-east of Baden-Württemberg as wellas in Franconia, parts of the Bavarian Forest
and the Eifel and Westerwald regions inRhineland-Palatinate. Although the summer
months vary in their long-term behaviour,
they have in general become drier.

6

One major aim of KLIWA is to record variability and changes in climatological parameters
and water budget components. This provides
the data for further comparative observations. A monitoring report is published forthis purpose every 5 years (last updated
2016) at www.kliwa.de

RISE IN AIR TEMPERATUREFROM 1931 TO 2015
The diagram shows the change
in areal mean air temperature
in hydrological six-monthly periods. Temperatures have risen
by more in the winter (+1.3 to+1.6°C) than in the summer(+0.8 to +1.2°C).

CHANGE IN AREAL
PRECIPITATION FROM 1931
TO 2015The diagram shows the change in areal precipitation in thehydrological six-monthly periods.
The figures show clear seasonal
differences: changes are unevenin the summer half of the year
whereas, in contrast, precipitation has generally increased in
the winter months by between
9% and 20%. In the last 15
years the trends for the winterhave weakened while there has
been more precipitation in thesummer.

7

I N S TR U MEN TS O F
C L I MATE R ES EAR C H

3Modelling future developments
Instruments of climate research
There can no longer be any doubt that climate change is happening. The carbon dioxide which has already beenreleased into the atmosphere will continue to have an effect there for several decades and will cause further
global warming. Adaptation measures are therefore essential. Global and regional climate projections do not provide
enough information on their own about the impact of global warming on water resources management. Changes inrunoff, and in floodwater or low-water situations in particular, can only be determined using high-resolution watermodels driven by regional climate models.

CLIMATE MODELLINGDATA BASIS FOR
WATER MODELS

Water models are createdusing extensive digital data
records (e.g. digital elevation
models, satellite classification of land use, soil properties and riverine networks).
Up to 16 different land use
scenarios are computed foreach separate grid square,each with its specific evaporation and runoff characteristics.

Weather, weather conditions and climate:in meteorology and climatology these three
concepts stand for processes which unfold
over varying periods of time. Weather describes the condition of the atmosphere overa short period of time, weather conditions
a phase of weeks or several months andclimate longer periods of time, ranging fromdecades through to geological ages.
With today‘s resources, weather forecasting is a difficult task and only possible fora period of 5 to 7 days at most. Producing
long-term projections of the way the Earth‘s
climate is likely to change is an incommensurably more complex task, as many parameters and magnitudes mutually influence eachother and not all processes are sufficiently
well understood. Global climate models arein all cases based on an atmospheric model
which is supplemented by ocean, snow,
ice and vegetation models. Anthropogenic
influences (the ‚human factor‘) are taken into
consideration in the form of various assumptions regarding greenhouse gas emissions(SRES scenarios) and, in the most recent
generation of climate models, radiation forcing (RCP scenarios).
The grid width of global climate models(with a grid width of about 200 km) is far toocoarse for estimating changes in regional
climate. Regional features such as mountain
ranges and river valleys can only be captured
by regional climate projections (~10 km). The
studies with SRES scenarios have now been
completed. Evaluations for the new RCP
scenarios are just beginning and will conti-

8

nue to be a task for the next years in KLIWA.
Even higher resolution climate projections(~2.8 km) are currently being considered
in order to capture convective precipitation
events more effectively.

ANTHROPOGENIC DRIVERS
IN CLIMATE MODELLING
RCP scenarios represent theadditional radiative forcing resulting from human activity; the„old“ SRES scenarios are shownin grey (sources: RCP database,
IPCC 2007). KLIWA currently
uses mainly the RCP scenario
8.5 and SRES scenario A1B.

WATER BALANCE MODELSThe impact of climate change on water
management is evaluated using climate-driven regional projections and water balance
models to simulate future discharge conditions. The link between an emission scenario – climate model – and a water model isreferred to as a model chain. Water models
facilitate the calculation of the spatial andtemporal distribution of essential components of the water cycle – such as evaporation, seepage, water storage and runoff.
These models can be used to quantify andassess the impact of changes on the water
budget and to develop adaptation measures.
Special soil water balance models are usedin addition to determine the groundwater
recharge. The findings are used to develop
adaptation measures and recommendations
for action, such as for low-water or flooding
conditions.

MODEL CHAIN FORREGIONAL CLIMATECHANGE STUDIESThe necessary links between themodels used to produce regional
climate projections and to simulate future discharge conditions
are shown schematically as amodel chain.

Emission
scenario

Globalclimate
model
(GCM)

Regional
climate
model
(RCM)

statistic

dynamic

Bias-Correction

Waterbudgeting
model
(WBM)

Regional climate projection
Runoff projection

RANGE OF RESULTS
The results of climate projections are subject
to a number of uncertainties. Several climate projections (ensemble approach) can beused to produce a range of possible futureclimates and to assess their variability andexisting uncertainties. Possible development
pathways have to be considered on the basisof several projections demonstrating a rangeof different potential changes.

9ADAPTATI O N
S TR ATEG I ES

4

Simulations for our future climate
Adaptation strategies
Various climate projections are available for the simulation of future conditions. Although the results of climate
simulations for the „near future“ of 2021-2050 differ from region to region, the general trend is the same: Warming
will continue, winters will be wetter and summers tend to become drier. The resulting changes in the water budget
call for adaptation strategies in water resources management.

RATHER HOT AND WITH LESS ICE
The regional climate simulations for southern
Germany so far considered in KLIWA showthat mean temperatures could increase by
0.6 to 1.8°C until 2050. Temperatures will,
however, increase by different amounts inthe summer and winter months.

Urlau an der Eschach flood retention
area

The current trend towards wetter wintersand drier summers will continue with up
to 10% less rain in the summer in someregions and with noticeably more precipitation – in some regions up to 30% – in the winter. Precipitation will continue to be highest
in the westerly oriented orographic windward areas of the KLIWA region. There will
also be considerably more winter days withextreme precipitation (25 mm or more); insome regions the number of such days will
even double. In contrast, there will be moresummer days without any precipitation. Thismeans that dry periods will last longer.

CONCLUSION UP TO 2050
As a result of the human-induced greenhouse effect, there will be•a significant increase in the number ofhot days (over 30°C) and of summerdays (over 25°C) compared to today,•
longer lasting summer droughts,•
more extreme precipitation events in thesummer with local flooding,•an increasing number of westerly
weather patterns which bring higher precipitation, particularly in the winter,•increasingly more winter precipitation asrain rather than as snow,

10•

fewer frost days (temperature lows of
0°C or less) and icy days (where thetemperature remains below freezing
point).

ADAPTATION STRATEGIESKLIWA studies originally focused on flood
flows. Now attention has shifted to theimpact of climate change on low-water
discharge, groundwater recharge and water
ecology. The studies also look at the potential increase in extreme precipitation eventsand accompanying soil erosion.
Climate change poses a tough challenge forthe federal states, local authorities and ultimately every citizen. The foreseeable and inpart already perceptible impacts of climatechange can only be met by concrete adaptation measures. For this reason effective androbust but flexible adaptation strategies must
be developed taking into account hydrological as well as political, social and economic
aspects. In this context, the principles ofsustainability and environmental compatibility
are equally important as uncertainties andinteractions between climate mitigation andadaptation.

RISE IN AIR TEMPERATURE
UP TO 2050
The diagram shows the change
in air temperature in comparisonof 2021-2050 vs. 1971-2000.
These figures depict the previous
basis in KLIWA with changes
taken from SRES A1B comparedto the changes in more recent
climate projections based on
RCP8.5 (15th and 85th percentile). Winter and summer temperatures will continue to rise.
For the most part summer temperatures will change less thanwinter temperatures.

CHANGE IN AREAL
PRECIPITATION UP TO 2050
The diagram shows the change
in areal precipitation in comparison of 2021-2050 vs. 1971-2000.
These figures depict the previous
basis in KLIWA with changes
taken from SRES A1B comparedto the changes in more recent
climate projections based on
RCP8.5 (15th and 85th percentile). The changes differ according
to season: on the whole, winterswill be wetter and summers
drier.

11

G R O U N DW ATER

5

Our most important drinking water reservoir
Groundwater
In southern Germany about 80 per cent of the drinking water supply is extracted from groundwater. The impact ofclimate change on groundwater resources is already apparent and is of particular importance for water management
issues. As climatic conditions change, it is essential to ensure the supply of drinking water in the future.

MEASUREMENTS REVEAL CHANGES

Our springs are still bubbling fromabundant groundwater.

Groundwater levels and the spring discharges have been observed at certain gauges
for decades, in some cases for even morethan a century. The obtained time series
contain information about the long-term
development of groundwater levels andspring discharges. Systematic evaluation of
selected time series for the most important
groundwater aquifers in Baden-Württemberg,
Bavaria and Rhineland-Palatinate reveals
declining conditions at about 2/3 of thestudied gauges. Simultaneously, the annual
maximum value is now measured earlier inthe year at most gauges - a direct consequence of warmer winters and decreasing
snow cover.
DEVELOPMENT OF GROUNDWATER
RECHARGE
By applying a soil water balance model,
joint extensive simulations for the period
from 1951 to 2015 have been performed
for southern Germany. The results of thesecalculations can be used to examine thechanges in the past. Average groundwater
recharge in southern Germany (see figure
top right) over the entire period was 185
mm. The figures for particular years show
that, in the recent past, groundwater recharge has occurred at no more than an averagerate (see figure bottom right). Thus, mean
groundwater recharge in 2003 was only 157
mm. Regarding the WETTREG2010 projection, mean groundwater recharge rates of
144 mm can be expected in the near future(2021-2050). Due to distinct temperature
increases and decreasing precipitation

12

throughout the entire year, WETTREG10 can
be considered as „worst case“ scenario.
The drought index also shows an increase
in dry periods. The drought index defines
the yearly number of days with a soil watercontent below 30% of the available watercapacity. No infiltration takes place during
this period and vegetation suffers from severe dry conditions. While there was a deficit
in soil water on an average of 52 days per
year during the entire period, this figure hasrisen to 61 since 2003. In the near future an
average of 70 days per year is anticipated(WETTREG2010).

MEAN ANNUALGROUNDWATER RECHARGEFROM PRECIPITATION –LONG-TERM AVERAGE(1951-2015)
Groundwater recharge is highly
relevant for water management
and is an important measure forthe natural regenerative capacityof groundwater resources. Under
the auspices of KLIWA, the formation of new groundwater inthe period 1951-2015 has been
calculated for all three federal
states applying a soil waterbalance model.

RECOMMENDATIONS FOR ACTION
Regular observation of groundwater quantity and quality is essential for sustainablegroundwater management. The observation
network must therefore be maintained consistently to monitor the impact of climatechange. As it already became evident in thepast, extended summer droughts can leadto water shortages for short periods in particular areas. Efforts to avoid potential water
shortages will need to include regional andsuperregional networking solutions. Above
all, the increasing demands from agricultural
irrigation call for sustainable concepts thatavoid conflicts between stakeholders/interest groups and ensure water supply in the
future. The increasing frequency of extreme
weather events associated with climatechange may lead to temporarily higher local
and regional groundwater levels. These havethe capability to damage buildings and infrastructure. This must be considered in thedesignation of boulding areas in potentiallyaffected areas of high groundwater levels.

MEAN ANNUALGROUNDWATER RECHARGEFROM PRECIPITATION(1951-2015)
Development of annual groundwater recharge from precipitation
in southern Germany (BadenWürttemberg, Bavaria andRhineland-Palatinate) from 19512015. The long-term figures forthe 1951-2010 period are plottedfor comparison.

13

L O W W ATER

6

More frequent and longer lasting drought
Low water
The drier and hotter summers which are expected in the future will lead to lower water levels. These low-water phases not only pose difficulties for inland waterway shipping, but also afflict agriculture, the energy industry, drinking
water supply as well as commercial and industrial enterprises requiring water for their production processes (e.g. thepaper industry). Long lasting dry periods can have serious economic impacts and result in substantial financial losses.
Furthermore, drought conditions not only affect water management, low water levels also influence and harm water
ecology.

NEGATIVE DEVELOPMENT OF THE
WATER BUDGET IN RIVER BASINS

Low water on the Altrhein in
November 2015.

Climate change and global warming lead toan intensification of the hydrological cycle
and to more frequent extreme weather
events. The flash floods of 2016, with toomuch water at one place in a very shorttime, occurred in a longer period withtoo little water over a much greater area.
Groundwater levels were already very low
before the hot summer of 2015 and only
recovered slightly in the following dry winter.
Consequently there was much less water instreams and rivers than would normally be
the case. Water management will need toadjust to such situations in the future.
LESS RAIN AND MORE EVAPORATION= LESS RUNOFF IN SUMMER
Most gauging stations in BadenWürttemberg, southern Bavaria and someparts of Rhineland-Palatinate show a longterm fall in water levels during the summer
months (1951-2015). These changes aremost pronounced in the months from Juneto October, although their actual severity
varies from region to region. In contrast,
water levels in northern Bavaria and parts ofRhineland-Palatinate have changed very little;
in fact, low-water discharge has been evenhigher.
In relation to the common KLIWA ensembleof runoff projections for southern Germany,
climate change is producing regional varia-

14

tions in low water in the summer half-year
exemplarily shown at selected gauging
stations. Most gauges tend to show a small
reduction in low-water discharge of around
15%. However, some gauges may not show
any clear change or just slight increases inrunoff. In the near future there will be very
little change in the low-water situation during
the winter half-year. Throughout the courseof the century the low-water situation is
expected to become more critical throughout southern Germany during the summer
half-year, i.e. with lower runoff and more
frequent phases of low water.

INFLUENCE OF LOW
WATER ON ECOLOGY AND
ECONOMY
Many water management usesand ecological functions may be
impaired by low water, either
because they require a sufficientvolume (quantity) or type (quality)of water. There are also complex
interactions between these types
of use. A reduction of water
availability consequently leads toconflicts of interest.

Höhenmodell
30 x 30 m

Landnutzung
30 x 30 m

Bodeneigenschaften

Flussnetz

Vernetzung derRasterflächen

WHAT NEEDS TO BE DONE?
A package of measures will be needed tomitigate the impact of more frequent low
water and dryness. These may be short-term
operational measures, such as restricting or
prohibiting water abstraction during particular
low-water situations. However, long-term
measures, such as supporting seepage orincreasing of large scale water retention, arealso needed in order to have a preventive
effect on future low water events. This will
require coordination with all the affected stakeholders in order to lower conflicting use as
far as possible. KLIWA studies the effects,
conflicts and options for action on low waterin case studies. Stress tests which simulate
particularly extreme low water conditions
provide input for discussion on the appropriate responses to such situations.

CHANGE IN MEAN LOWWATER DISCHARGE IN THE
NEAR FUTURE
Change in mean low-water
discharge in the hydrological summer half-year (May to October)comparing the near future (20212050) and the reference period(1971-2000). Selected gauges in
Baden-Württemberg, Bavaria andRhineland-Palatinate are shown.

15

F L O O DI N G

7„Flexible and no regret“ strategy
Flooding
The prospects on possible climate developments for the next few decades is afflicted with uncertainties. However, all
the flooding studies carried out to date do show that there will be more flooding events in the future. Flexibility andthe precautionary principle are appropriate given the spread of possible results in relation to adaptation. Adaptation
does not, however, mean building protective walls everywhere. Preference must be given to flood risk management
measures which are effective in the long term, which cover a broad spectrum and, as far as possible, are also usefulfor other aspects.

INCREASING RUNOFF, MORE
FLOODING EVENTSFLOOD PROTECTION –WHAT DOES IT MEAN IN
PRACTICE?
Example Flood embankments:
Embankments will be built
as originally planned leaving
an area on the outside clear
so that they can easily bebroadened and raised if
necessary.
Example Bridges:
The regional climate change factor will be taken into
account when bridges areplanned as subsequent
adaptation is often impossible for technical reasons.
Example Retaining walls:
New retaining walls will be
designed to enable additionalheight to be added easily inthe future if needed.

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Concerning flood discharge, climate change
is statistically detectable since around themid 1970s. Simulations based on waterbalance models for the river basins in thethree KLIWA federal states show that flood
discharge levels will continue to increase inalmost all regions, especially in winter. Since
the beginning of the 2000s, strategies andstipulations have been implemented whenplanning new flood protection measures, on
how climate change could already be accounted for in their dimensioning. Along the River
Neckar, for example, the figures for a 100year flood (HQ100) must now be multiplied
by a climate change factor of 1.15. In otherwords, in the future flood protection systems
must be designed to cope with a 15 per centhigher discharge than today‘s values indicate,or at least be planned in such a way that they
can be adapted to meet higher requirements.
HQ100 is the flood discharge which, statistically, is only exceeded once every 100 years(see image top right).
ADAPTATION MEASURES FOR
CLIMATE CHANGE
The impact of climate change on flood
discharges varies from region to region. For
example a climate change factor of 1.25
has been calculated for the Upper Danube
area of Baden-Württemberg. Smaller floods,
and floods of moderate severity, are also
expected to increase. The HQ5 discharge fora flood on the Upper Danube – which today
can be expected to occur on average every
five years – has gone up by 67 per cent.
This means that, in the future, the current

HQ5 value for the Upper Danube must be
multiplied by a climate change factor of 1.67.
The HQ5 climate change factor for the areaaround the tributaries to the Upper Rhine
is 1.45, for example. The factor is lowest(1.24) in the Upper Swabia / Lake Constanceregion.
A climate change factor based on the first
KLIWA 2004 study findings has also been
introduced in Bavaria – here the statisticalvalue of HQ100 was increased by 15% statewide. Plans for new flood protection measures are therefore already taking account of
the expected effects of climate change. The
fundamentals of the climate change factor
are continuously reviewed and expanded
by further research. So far, these results
have confirmed the 2004 stipulations. In
Rhineland-Palatinate flood protection measures are always dimensioned according to theactual side constraints which apply in eachindividual case, with a particular focus on thethreat to the population, the potential damage caused by flooding and considerations of
economic viability. Runoff studies have been
carried out in recent years for the wholeof Rhineland-Palatinate and for the Middle
Rhine. Initial results for the Upper Rhine in
Rhineland-Palatinate show that there will bea significant increase in smaller flood discharges, i.e. discharges with a higher probabilityof occurrence, in the „near future“ (2021 to2050). These discharges (which are expected
to increase in frequency) already occur inareas which are protected by dykes, and aremanageable with flood retention and technical flood protection measures.

CLIMATE CHANGE MARKUPIn planning the dimensions of flood protection facilities, a markup
on the current value for flood discharge takes account of the possible effects of climate change. The freeboard margin prevents thebreaching of a flood protection barrier (e.g. as a result of higher
water levels caused by waves and wind).
THE SPECIAL CASE OF THE UPPER RHINE

Owing to the special situation for the Rhine, such asdischarge from Switzerland and water regulation measures along the river‘s upper reaches, the stretch of theRhine from Freiburg to Mainz was not included in the firstdischarge studies performed as part of KLIWA. Robust
climate projections are now available for the entire Rhine
catchment area – including its Swiss part. There are also
suitable water balance models which cover the retention
effect of Lake Constance, the large lakes on the edge of
the Alps and the entire Rhine catchment area up to Worms(approximately 69,000 km²). The flow of water down the
Rhine as far as Worms is strongly influenced by the runoff
formation in the Swiss Alps and therefore the seasonal
cycle of snow build-up and thawing. The largest discharges
occur in the hydrological summer half-year from May to
October. Analyses of relative changes between the futurescenario 2021-2050 and the current status 1971-2000
for the water level of the Rhine show that no substantialchanges are expected for mean flood discharge. With the
exceptions of the months of May and October, results
even show a slight decrease in mean flood discharge forthe summer half-year during which the highest discharges
occur. Increases of less than 10% are simulated in thewinter half-year from November to April. From today‘s
point of view no increases in mean flood discharges are
discernible at Rhine gauges up to 2050. The values for extreme flood discharges tend to be higher. Nonetheless they
are significantly lower at gauging stations in a nival (i.e.
influenced by snow melt) regime than at gauging stations
in a pluvial (i.e. influenced by rain) regime. The increase in
HQ100 at gauging stations in a nival regime on the Upper
Rhine, for example, reaches from +3% to +5% (Basel,
Maxau, Worms) and is as such significantly lower thanat gauging stations in a pluvial regime, like at Rockenau(Neckar) with +12%. These Upper Rhine trends are passed on for the most part to the Middle Rhine (Mainz, Kaub)although even higher extreme flood flows may occur
below the mouth of the Mosel.

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EXTR EME
PR EC I PI TATI O N

8A growing danger?
Extreme precipitation
Extreme precipitation events are characterised by a large amount of rainfall in a short period of time. They usuallyoccur in a small area and the risk of flooding is hard to estimate. Climate change and the warming projected in the
future significantly increase the potential for higher volumes of precipitation and thus the risk of more frequent andmore extreme precipitation events. However, these are also countered by other meteorological factors, such as changes in weather patterns.

EXTREME PRECIPITATION

Extreme precipitation eventin
Braunsbach, 29 May 2016

Long-term trends in the frequency and intensity of extreme precipitation can only be distinguished from natural variability with measurements taken over many decades. Trend
analyses concerning extreme precipitation
are more difficult because those events are
not always captured by the precipitation
measuring network. Maximum one-day areal
precipitation quantities have been studied
in KLIWA. These increased throughout
almost all of southern Germany in the period 1931–2015, although statistical certainty
and strength (maximum +33%) vary greatly
between regions. There is as yet no clearly
discernible trend for the summer half-year.
Flash floods and soil erosion are usually triggered by short-duration events which may
constitute a part of the studied daily precipitation but which cannot be clearly separated
from it.
The available data to analyse precipitation
over periods of less than 24 hours is muchworse. Analyses of the radar data available
in Germany for the last 15 years clearly point
to a regional increase in short-lived burstsof extreme precipitation. However, owing to
the short length of the available time series
these results are still climatologically inconclusive. Still, they can usefully supplement
the evaluation of station data and be compared with a subperiod, for example. Further
research is required to produce more robust
findings. This also applies to climate projection data. Models which allow for convection
should certainly be used in this context for
short-duration precipitation. While projections

18of this kind already exist, the existing data
for ensemble evaluations are only just being
successively created.

CHANGE IN MAXIMUM
AREAL PRECIPITATIONFROM 1931 TO 2015
Development of maximum oneday areal precipitation volumes in
the hydrological winter half-year,
relative trend (change stated aspercent, deviation from 19312015 mean).

ADAPTATION – WHAT CAN LOCALAUTHORITIES DO?
As convective precipitation falls locally and isdifficult to predict it can, in principle, affectany community. Local authorities should therefore consider the potential dangers arisingfrom extreme precipitation to people anddamage to buildings and infrastructure andshould take suitable precautionary measures. Diverse activities are being undertaken
at the state level in this respect: BadenWürttemberg and Rhineland-Palatinate havepublished a joint guide entitled „Heavy rainfall – What can local authorities do?“. Landuse can be adapted to minimise the risk oferosion and related impacts as far as possible (see also „Codes of good practice“ foragricultural land).
A further guideline on the managementof extreme precipitation events by local
authorities has also been produced in BadenWürttemberg. This guideline offers local
authorities a standardised procedure for the
analysis of dangers and risks as the basis ofa local authority action plan. Local authorities
can use extreme precipitation maps to predict where surface discharge will accumulate
and where it will run off. On this basis measures can be developed to avoid damages as
far as possible in cases of emergency. The
focus throughout is on public institutions,infrastructure, housing estates, commercial
and industrial estates and on informing the
public and all stakeholders about the risk ofextreme precipitation.

EXTREME PRECIPITATION AND SOIL EROSION
The risk of soil erosion varies greatly from region to region
depending on a number of influencing factors (precipitation, land and ground properties and management). The frequency and intensity of heavy rainfall are the triggering factors, however. Any future change in these factors can be
expected to increase the risk of soil erosion and the associated threats. Soil erosion causes long-term ecological andeconomic damage. Fertile soil is lost on the areas affected
and soil functions are impaired. Neighbouring areas andstructures are affected by deposited soil material. Nutrientsand pollutants attached to soil particles find their way into
other ecosystems, e.g. waters. Changes in precipitation
intensities are studied in KLIWA in high-resolution datatime series and climate models.

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AQU ATI C EC O S Y S TEMS

9Impact on water quality
Aquatic ecosystems
Climate change affects inland waters and the animals and plants that live in or around them. Rising temperaturesand falling discharge or water levels strain the oxygen balance and change the composition of biotic communities.
This could have an enduringly negative impact on the good status of our waters. However, what has in fact changed and what changes can we expect in the future? Conclusions are difficult to reach owing to the intricate andentangled interactions between water characteristics and ecological systems as well as the relative paucity of specific data.
VARIETY OF INFLUENCES ON
WATER ECOLOGYThe European bullhead needs highconcentrations of oxygen and low
water temperatures. It is therefore
strongly affected by climate change.
Photograph: Fisheries ResearchCentre Baden-Württemberg

Climate change alters some of the fundamental factors in streams, rivers and lakes,
such as water temperature, the depositing
and dispersion of fine-grained sediment, theconcentration of nutrients or their blendingin lakes. All this triggers an entire chain ofprocesses which can ultimately affect water
habitat flora and fauna with some species
becoming rarer and other new plants colonising the areas. Changes take place in biotic
communities and the functionality of theaquatic resources. While the impact of climate change on water resources in southern
Germany has already been comprehensively
modelled, until now changes in water ecology are only known to have occurred in smaller areas. For instance, a tendency of biotic
communities to move upstream in rivers andstreams could already be proven locally.
Two literature studies commissioned by
KLIWA illustrate the interacting effects ofclimate change and the quality of rivers,
streams and lakes at the regional level inthe three federal states of Bavaria, BadenWürttemberg and Rhineland-Palatinate.
These studies, and the extensive literatureand sensitivity analyses which go with them,demonstrate that changes in the quality ofwater may be expected in many areas in
the future, but at the same time also reveal
many areas in which there are still knowledge gaps and action needs to be taken.

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FUTURE MONITORING
Until today it is not possible to say just what
influence climate change will have on thequality of our inland waters. The most recent
monitoring programme on flowing water
is to be supplemented by special climate
impact monitoring in order to obtain robust
data. The concept for such a programme ofbodies of flowing water is almost complete.
The aim of monitoring is to provide a fundof data which can be used to address many
issues in the future and to find and define
appropriate adaptation measures.
CLIMATE CHANGE INDICATORS FOR
WATER QUALITY
Creating a good database is only the firststep, however. Ways must be found toevaluate data which differentiate between
the influence of climate change and otherfactors on aquatic environments. New
indicators are needed for this purpose. An
indicator for flowing water has already beendeveloped in KLIWA.
The KLIWA indexMZB appears to be a suitable tool for „measuring“ changes in thespecies composition of small organisms
living at the bottom of an aquatic ecosystem(freshwater benthic invertebrate fauna). Suchchanges – through to species which toleratehigher temperatures and lower oxygen levels– may be anticipated as climate change inthe summer worsens aeration conditions(mainly in the form of higher water temperatures and lower flows speeds). A field test is
currently being run to clarify the applicabilityof the index.

INTERACTIONS BETWEEN
CLIMATE CHANGE AND THE
QUALITY OF RIVER AND
LAKE HABITATSClimate change has a direct
impact on the water temperatureand the flow characteristics ofrivers and streams. These two
factors determine a number ofprocesses which have a critical
impact on the supply of oxygen
and therefore on the crucial
conditions of life for water organisms. Illustration: Martin Halle /Andreas Müller

THE SENSITIVITY OF
MOUNTAIN STREAMS
Small Kerbtal (notched valley)
streams, like the Endertbach
in Rhineland-Palatinate, have ahigh level of flow and substrate
diversity. They are cold and well
supplied with oxygen. Their species-rich invertebrates may beparticularly prone to changes in
the climate. Photograph: Jochen
Fischer

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WATER TEMPER ATU R E

10Hot summers, warm rivers and lakes?
Water temperature
Water temperature is a key quality parameter. It determines all biological and chemical properties in a body of water.
It also influences the use humans make of water in many different ways: for leisure, as a source of nutrition or as ameans of cooling power stations and industrial installations. The warming of air leads to warming of streams, rivers
and lakes.

FLORA AND FAUNA ARE SENSITIVETO TEMPERATURES

Shady banks reduce the warming
up of water by the sun

Water temperature has a huge influence on
biological and physical/chemical processes
in bodies of water and affects the speed of
metabolic processes. This means that watertemperature has a direct impact on all theorganisms living in a water body and is also
relevant to the composition of aquatic biotic
communities, to effective photosynthesis, tothe fish mortality rate, internal water metabolic rates, the solubility of gases and the
toxicity of many environmental chemicals.
Various regional guide values are available forwater temperatures which are tolerable forfish in particular. These are stipulated in thefederal surface water ordinance (OGewV).
Fish communities may be endangered if
these values are exceeded.
THE WATER IS GETTING WARMER
TOO
Initial studies have been made of watertemperatures measured in Bavaria between 1951 and 2009. These show that themean annual water temperature has risen
by around 1.5°C since 1980. Temperaturesappear to have risen everywhere. The trend
is especially apparent in the summer months
from May to August. Comparable studies
on the Rhine also show an accumulation of
maximum summer values of over 25°C. In
the last decade, water temperatures havereached daily mean values of over 28°C anddaily maximum values of over 29°C. Most of
the water temperature rise is due to seasonal and regional climatic influences.

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Restrictively mentioned, however, this heating is further exacerbated by human interventions, such as the discharge of heat into
water or the building of damming structures.
Consequently is not possible to distinguishthe causes and influences entirely in every
single case. A fundamental increase in
the average temperature of flowing water
immediately reduces the amount of warmingfor other uses which would be ecologically
acceptable. On extremely hot summer days,for example, it is necessary to reduce theinflow of warmed waste water into water
which is already hotter owing to climate
influences. This is directly followed by economic consequences.
WILL IT GET EVEN WARMER?
The modelling of further temperature changes in water bodies is of great interest forstatements about the future development.
However modelling is difficult as many factors in addition to discharge also need to betaken into account. While a statistical approach has already delivered initial findings in
Bavaria, a physically-based modelling approach with water budget heat models is being
taken in Baden-Württemberg and RhinelandPalatinate. The use of climate projections
in both approaches enables some initialconclusions to be drawn about the extent towhich climate change will impact water temperature in the future. Climate projections
provide an important input for further studyof changes in water ecology.

CHANGE IN MAXIMUMWATER TEMPERATURE IN
BAVARIAThe maps show the mean change in the maximum daily watertemperature between the two
periods 2021-2050 vs. 1971-2000
using three climate projections.
Overall the temperature rises by
between +0.5 and +1.3°C.

Future prospects / outlook
We must expect increasingly hotter and drier summers and milder and wetter winters in the future.
The change in the distribution of precipitation in particular will have a sustained impact on the regional water cycle and, as a result, on the water balance of our river basins.

KLIWA initially focussed on the problems presented by flood hazards and has elaborated distinct measures for
dealing with these. The main emphasis of investigation has now shifted to the effects of climate change on
low-water discharge, groundwater, the management of heavy rainfall and water ecology.
Changes to the water cycle have direct consequences for the many different water uses – whether as directly
tapped for drinking water and agricultural irrigation, for use as a coolant in power stations or as a transportroute for shipping or various leisure uses. This is linked to the question of the effects of climate change on
the quality and ecological status of our waters; this is one of the main areas of work in KLIWA at present. The
focus will also be on the potential increase in extreme short-term precipitation. This extreme precipitation may
cause enormous local flooding and create even more problems for local authority drainage networks or, as aresult of soil erosion, result in substantial damage for agriculture and high depositions in our waters.
Regional measures that seek to cushion the effects of climate change are one thing – but even more important are steps dedicated to active climate protection. Top priority must be given to reducing greenhouse gas
emissions. The delayed response of the climate system means that even if emissions were to come to an
immediate stop (a purely fictitious scenario), temperatures would keep rising in the immediate future. Eachand every one of us must therefore take action to ensure that future generations are not confronted with evenmore serious problems.

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