Future Alpine hydropower productionImpacts of climate change, environmental flow and technical optimization on Run-of-River power plants in Switzerland

Session HS5.3.2

Wechsler Tobias1,2,3,5, Stähli Manfred1,5, Zappa Massimiliano1,5, Jorde Klaus4,5, Schaefli Bettina2,3,5

1Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland2Institute of Geography, University of Bern, Hallerstrasse 12, 3012 Bern, Switzerland3Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Falkenplatz 16, 3012 Bern, Switzerland 4KJ Consult, Ferdinand-Raunegger-Gasse 26, 9020 Klagenfurt, Austria5Swiss Competence Center for Energy Research – Supply of Electricity (SCCER-SoE), Sonneggstrasse 5, 8092 Zurich, Switzerland

Research questions• How will Run-of-River (RoR) power production in Switzerland change

under climate change? • What does the climate induced change in hydropower (HP) production

mean compared to the potential increase by optimizing the design discharge or to losses due to environmental flow requirements?

MethodToassessclimatechangeimpacts,dailyrunoffuntiltheendofthecenturywascalculatedwiththehydrologicalmodelPREVAH,usingatotalof26climatemodelchainsintransientsimula-tionfromthenewSwissClimateChangeScenariosCH2018,correspondingtothetwodiffer-entCO2emissionscenariosRCP2.6(withtheassumptionofconcertedmitigationefforts)andRCP8.5(withtheassumptionofnoclimatechangemitigation).ChangesinHPgenerationun-derclimatechangeareestimatedforelevenRoRpowerplantsbasedondifferencesintheflowdurationcurves(FDCs)betweenthereferenceperiod(1981–2010)andthefutureperiodsmid-century(2045–2074)andendofthecentury(2070–2099),assumingunchangedinstalledmachineryandenvironmentalflowrequirements(Fig.1).ThechangesinHPproductionfromRoRpowerplantsdependsmainlyonthechangeintheusablewatervolume,whichiscontrolledbythedesigndischargeofthepowerplantandtheenvironmentalflowregulations.Thepotentialofthedesigndischargeisestimatedinthisstudybyassumingthatitequalstheflowwhichisexceededat80%percentilebasedonthemeanFDCofthereferenceperiod(Fig.1).Thelossduetoenvironmentalflowregulationsiscom-paredwiththescenarioasiftherewerenoenvironmentalflowcurrently.

RoR plant Wildegg/Brugg – Aare RoR plant Davos Glaris – Landwasser(atypicalriveroftheSwissplateau) (atypicalalpineriver)

ThewatervolumeusableforHPproduction(shadedarea–Fig.1)dependsmainlyonlowandmediumwaterranges.FortheRoRpowerplantWildegg-Brugg,thehydrologicalpredictionsindicatethatboththeaveragewatersupplyandtheannualproductionwilldecreaseinthefu-ture(Fig.2left).FortheRoRpowerplantDavosGlaris,whichisheavilyinfluencedbysnow,thetotalwatersupplywilldeclinebytheendofthecentury;still,HPproductionislikelytoin-creaseduetothechangeinthelowerandmediumwaterrange(Fig.2right).

ResultsChange in mean annual productionfor eleven selected RoR power plants

Change in mean winter production (Oct – Mar)

Fig.3.Expectedchangesinannual(above)andwinter(below)productionofselectedSwissrun-of-riverpowerplantsfortheperiods2060(mid-century,2045–2074)and2085(endofcentury,2070–2099).ThecalculationsarebasedonthemostrecentClimateChangeScenariosCH2018establishedbyMeteoSwiss(21climatemodels;twoemissionscenarios:withconcertedmitigationeffortsRCP2.6andnoclimatechangemitigationRCP8.5)andastate-of-the-arthydrologicalmodel(PREVAH),takingintoaccountcurrentinstalledmachineryandenvironmentalflowrequirements.

Overall projection for RoR power production in SwitzerlandClimateinducedchangesinproductionareduetochangesinprecipitation,temperatureandevaporation,whichinturnhaveastrongimpactonthedominanthydrologicalprocesses(snowaccumulationandmelt,glaciermeltandrunoffproduction),andshowimportantspatialandtemporaldifferences.Climatechangeimpactonproductionfor theelevenconsideredRoRpowerplants(Fig.3)means:

FortheelevenRoRpowerplantsundercurrenthydrologicalconditions,• thepotentialthatcouldbeachievedbyoptimizingthedesigndischarge(Qdpot=80%per-

centile)isanincrease of 6% inproduction.• Compliancewithlegalconstraintsonenvironmentalflowrates,comparedtonoresidual

flow,meansadecreaseof4%inproduction.

ReferenceSCCER-SoE, 2019:Climate change impact onSwiss hydropower production: synthesisreport. Swiss Competence Center for Energy Research – Supply of Electricity. Zurich,Switzerland.28p.

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Change in annual production [GWh/year]

10%5%

0%1.5%

-1.5%-5%

-10%

2060 2085

RCP26

RCP85

< 50 GWh/a< 200 GWh/a< 400 GWh/a< 500 GWh/a> 500 GWh/a

Change in winter production [GWh/winter]

< 50 GWh/a< 200 GWh/a< 400 GWh/a< 500 GWh/a> 500 GWh/a

2060 2085

RCP26

RCP85

10%5%

0%1.5%

-1.5%-5%

-10%

Fig.1.Flowdurationcurves(FDCs) for theRoRpowerplantsWildegg-Brugg(Aare; left)andGlaris(Land-wasser;right).Theblacklinerepresentsthereferenceperiod(1981–2010),thegreyshadedarearepresentstheusablewatervolumecontrolledbythedesigndischargeandtheenvironmentalflowrequirements.TheareasboundedbyyellowcurvesandpurplecurvesrepresenttherangeofFDCsfortheprojectedRCP2.6andRCP8.5emissionsscenarios,respectively,fortheendofthecentury.Qdrepresentsthecurrentdesigndischarge;Qdpotthedesigndischargeatthe80%percentileifitisnotexceededyet.

Fig.2.Theexpectedchangesintheannualmeandischarge[MQ]andmeanproduction[GWh/a]attheWild-egg-Bruggpowerplant(left)andattheGlarispowerplant(right)fortheendofthecentury.Theblacklineindi-catesthemedianvalueofthereferenceperiod.Theyellow(RCP2.6)andpurple(RCP8.5)boxplotsrepresenttherangeofthedifferentmodelchainsundercurrentdesigndischargeandenvironmentalflowrequirements.

Qd

Qd

Qdpot

0%

-3%

-2%

-7%

6%

8%

5%

10%

2060 2085

RCP2.6

RCP8.5

2060 2085

RCP2.6

RCP8.5

Future annual production Future winter production

RCP2.6

RCP8.5

RCP2.6

RCP8.5

0%

-3%

-2%

-7%

6%

8%

5%

10%

2060 2085

RCP2.6

RCP8.5

2060 2085

RCP2.6

RCP8.5

2060 2085 2060 2085