Can we foresee the impact of climate change on runoff ... · National Environmental Research Institute • Department of Freshwater Ecology Climate change impact on diffuse dissolved

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National Environmental Research Institute • Department of Freshwater Ecology

Can we foresee the impact ofclimate change on runoff, nutrientlosses, river morphology andecology in Denmark

Brian Kronvang, Søren E. Larsen and Niels B. OvesenDepartment of Freshwater ecology

NERI, Denmark

A CONWOY contributionwww.conwoy.ku.dk


Potential impacts on the linked

catchment, river, floodplain and lake system

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Hindcasting of precipitation andriver hydrologyHypothesis• Mean annual precipitation has changed during the

last century.• River discharge will reflect these changes both

annually, seasonally and in the case of extremes(peak flows, droughts).

• A gradient in precipitation and hence changes indischarge can be expected across Denmark.

• Changes in land use during the last century (arableland, drainage, urban areas, groundwaterabstraction) could counteract or accelerate theclimate signal on river hydrology.


Investigated:

5 climate stations(red)

17 river stations(blue)

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Period CatchmentArea

(km2)Western JutlandBrede Å 1921-2001 290Ribe Å 1934-2001 675Skjern Å 1920-2001 1055Northern JutlandLindenborg Å 1925-2001 214Lindholm Å 1917-2001 106Årup Å 1936-2001 105Uggerby Å 1917-2001 153Eastern JutlandGudenå, Åstedbro 1917-2001 184Gudenå, Tvilum 1917-2001 1282Århus Å 1919-2001 119FunenOdense Å 1917-2001 302Brende Å 1918-2001 71ZealandSaltø Å 1918-2001 64Tude Å 1932-2001 148Harrested Å 1921-2001 16Suså, Holløse 1934-2001 763Åmose Å 1920-2001 292Tryggevælde Å 1917-2001 129


Other factors than climateinfluencing changes in runoff

• Land use changes during last century(drainage, urban development, agriculture,forest).

• Changes in drinking water and irrigationwater consumption.

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Daily mean discharge 1920-2001Stream Tryggevælde (Zealand)


Daily mean discharge 1920-2001Skjern river (western Jutland)

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Udvikling i årlig gennemsnitsnedbør forDanmark (øverst), samt årsafstrømningeni henholdsvis Skjern Å (midt) og Tude å(nederst).


Changes inannualprecipitationfrom 1931-60 to1961-1990

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Changes in annualprecipitation at 5climate stationsand runoff forDanish riversduring a 75 yearperiod.

*Significant(p≤0.05)


Trend i nedbør over året vedforskellige målestationer

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Trend i måneds middelafstrømningen i 10 vandløb


Trend i måneds maksimumafstrømningen i 10 vandløb

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Trend i måneds minimumsafstrømningen i 10 vandløb


Hindcast 1920-2001 (rød) ogfremskrivning (blå) 2001-2080 for ændringi måneds middel afstrømning i to vandløbfor perioden 1920-

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River morphology and sedimenttransportHypothesis

• River morphology will adjust to changes in climateand hydrology.

• Adjustments will take place during and for a periodfollowing climate and hydrological changes beforethe river again will be in a dynamic equilibrium.

• Sediment transport will increase due to highererosion and transport capacity/competence.

• Bank and bed erosion will increase.• Substratum composition will change.


Regime models for undisturbed Danishstreams in downstream directionStream widthMoraine landscape: w = 4.83Q0.61

Outwash plain: w = 5.59Q0.50

Stream depthMoraine landscape: d = 0.52Q0.47

Outwash plain: d = 0.60Q0.39

Current velocity:Moraine landscape: v = 0.40Q-0.08

Outwash plain: v = 0.30Q0.12

Mernild (2002) MSc Thesis, University of Copenhagen.

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Suspended sediment response toclimate change: an example

Q in m3/s and Css in mg/l

Strongly rising stage: Css = 80 • Q1.72

Winter (Oct-May): Css = 12 • Q1.37

Summer (June-Sept.): Css = 20 • Q0.99

Kronvang (1992) Water Research 26(10).


Nutrient losses

Hypothesis

• Nitrogen leaching will increase due to highermineralization and percolation of water through theroot zone.

• Phosphorus leaching will increase due to highermineralization and percolation of water through theroot zone.

• Phosphorus loss will increase due to increase inoverland flow (PP and DP).

• Phosphorus loss will increase due to increase inbank erosion.

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Climate change impact onnitrogen leaching from root zone

0

20

40

60

80

100

120

140

0 200 400 600 800

Annual percolation of water through root zone (mm)

An

nu

al le

ach

ing

of

nit

rog

en

(kg

N/h

a)

Western Jutland

12 kg N/haIslands

12 kg N/ha


Climate change impact on diffusetotal nitrogen loading of streams

0

5

10

15

20

25

30

35

0 200 400 600 800

Runoff (mm)

Dif

fuse

to

tal N

itro

gen

loss

(k

g N

/ha)

Sandy soilLoamy soil

6.5 kg N/ha4.9 kg N/ha

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Climate change impact on diffuse totalphosphorus loading of streams

0

0,5

1

1,5

2

2,5

0 100 200 300 400

Annual storm runoff (mm)

Dif

fuse

to

tal P

ho

sph

oru

s lo

ss (

kg P

/ha)

Sandy soilLoamy soil

0.15 kg P/ha

0.25 kg P/ha


Climate change impact on diffusedissolved P loading of streams

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0 200 400 600 800

Annual Runoff (mm)

Dif

fuse

dis

solv

ed in

org

nai

c P

-lo

ss (

kg P

/ha) Western Jutland

0.111 kg P/ha

Islands

0.059 kg P/ha

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Climate change impact on nutrient retention


Lake: 100 ha & 2 m average depth

catchment area = 1000 ha

Q = 400 mm

Q = 200 mm

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Stream ecologyHypothesis• The changing hydrological regime in streams will impact the

spatial and temporal extent of physical habitats and henceinfluence the biotic conditions.

• The more extreme hydrological conditions in streams, bothhigh flow and low flow, will create larger physcial disturbanceswith adverse impacts on the biological structure and diversity.

• Rising stream water temperature will impact the speciescomposition of macrophytes, invertebrates and fish in Danishstreams.

• Indirect impacts on stream ecosystems will also occur causedby changes in catchment pressures (substances), concentrationof dissolved oxygen in stream water, etc.


River, lakes and floodplains

Research under the CONWOY project - WP2• Hindcast of changes in longer time series of daily discharge in a

number of Danish rivers covering the west/east gradients inlandscape and climate.

• Forecasting of changes in river discharge by applyinghydrological models (NAM/MIKE11; MIKE-SHE/MIKE11.

• Analysis of changes in sediment mobilisation and transportapplying erosion models and development of statistical modelsbased on existing sediment concentration data.

• Analysis of changes in nutrient losses applying statistical anddeterministic models.

• Analysis of changes in sediment and nutrient retention applyingcoupled hydrodynamic and nutrient retention model.

• Dating of sediment cores to analyse historical changes insedimentation rates linked to climate/land use changes.

Can we foresee the impact of climate change on runoff ... · National Environmental Research Institute • Department of Freshwater Ecology Climate change impact on diffuse dissolved

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