DRAFT PAPER CLIMATE CHANGE IMPACTS ON THE OPERATION OF TWO HIGH ELEVATION HYDROPOWER SYSTEMS IN CALIFORNIA DRAFT

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1 CLIMATE CHANGE IMPACTS ON THE OPERATION OF TWO HIGH ELEVATION HYDROPOWER SYSTEMS IN CALIFORNIA DRAFT A Report From: Calforna Clmate Change Center Prepared By: Sebastan Vcuña, John A. Dracup, U.C. Berkeley; Larry Dale, Lawrence Berkeley Natonal Laboratory DRAFT PAPER DISCLAIMER Ths report was prepared as the result of work sponsored by the Calforna Energy Commsson (Energy Commsson) and the Calforna Envronmental Protecton Agency (Cal/EPA). It does not necessarly represent the vews of the Energy Commsson, Cal/EPA, ther employees, or the State of Calforna. The Energy Commsson, Cal/EPA, the State of Calforna, ther employees, contractors, and subcontractors make no warrant, express or mpled, and assume no legal lablty for the nformaton n ths report; nor does any party represent that the uses of ths nformaton wll not nfrnge upon prvately owned rghts. Ths report has not been approved or dsapproved by the Calforna Energy Commsson or Cal/EPA, nor has the Calforna Energy Commsson or Cal/EPA passed upon the accuracy or adequacy of the nformaton n ths report. Arnold Schwarzenegger, Governor Month 28 CEC-5-28-XXX

2 Acknowledgments We would lke to acknowledge Kevn Cn and Tom Watson from Southern Calforna Edson, Scott Flake and Dudley McFadden from Sacramento Muncpal Utlty Dstrct and Gudo Franco from the Calforna Energy Commsson. Fundng for ths project came from the PIER program of the Calforna Energy Commsson (Project No. MR-7-3A).

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4 Preface The Calforna Energy Commsson s Publc Interest Energy Research (PIER) Program supports publc nterest energy research and development that wll help mprove the qualty of lfe n Calforna by brngng envronmentally safe, affordable, and relable energy servces and products to the marketplace. The PIER Program conducts publc nterest research, development, and demonstraton (RD&D) projects to beneft Calforna s electrcty and natural gas ratepayers. The PIER Program strves to conduct the most promsng publc nterest energy research by partnerng wth RD&D enttes, ncludng ndvduals, busnesses, utltes, and publc or prvate research nsttutons. PIER fundng efforts focus on the followng RD&D program areas: Buldngs End Use Energy Effcency Energy Related Envronmental Research Energy Systems Integraton Envronmentally Preferred Advanced Generaton Industral/Agrcultural/Water End Use Energy Effcency Renewable Energy Technologes Transportaton In 23, the Calforna Energy Commsson s PIER Program establshed the Calforna Clmate Change Center to document clmate change research relevant to the states. Ths center s a vrtual organzaton wth core research actvtes at Scrpps Insttuton of Oceanography and the Unversty of Calforna, Berkeley, complemented by efforts at other research nsttutons. Prorty research areas defned n PIER s fve year Clmate Change Research Plan are: montorng, analyss, and modelng of clmate; analyss of optons to reduce greenhouse gas emssons; assessment of physcal mpacts and of adaptaton strateges; and analyss of the economc consequences of both clmate change mpacts and the efforts desgned to reduce emssons. The Calforna Clmate Change Center Report Seres detals ongong center sponsored research. As nterm project results, the nformaton contaned n these reports may change; authors should be contacted for the most recent project results. By provdng ready access to ths tmely research, the center seeks to nform the publc and expand dssemnaton of clmate change nformaton, thereby leveragng collaboratve efforts and ncreasng the benefts of ths research to Calforna s ctzens, envronment, and economy. For more nformaton on the PIER Program, please vst the Energy Commsson s webste or contract the Energy Commsson at (916)

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6 Table of Contents Executve Summary Introducton Methodologcal Approach Smulaton of hstorc operatons Development of future clmate change scenaros Case Studes Upper Amercan Rver Project SCE s Bg Creek System... Error! Bookmark not defned. 4. Results Hstorc operatons results and analyss of changes ntroduced Clmate change results Conclusons References Glossary

7 Executve Summary We present results of our work to estmate the mpacts of clmate change on two hgh elevaton hydropower systems n Calforna: the Upper Amerca Rver Projected (UARP) operated by Sacramento Muncpal Utltes Dstrct (SMUD) n Northern Calforna and the Bg Creek system operated by Southern Calforna Edson (SCE) n Southern Calforna. The study bulds on prevous work modelng the UARP system. The model presented here shows mprovements on that model that represent a better smulaton of hstorc operatons and mprove the methodology to project future operatons of both hydropower systems. The future operatons of these two hgh elevaton systems were smulated usng new clmate change scenaros provded for the Second Bennal Scence Report to the Calforna Clmate Acton Team. These new hydrologc condtons mean reduced runoff for both systems (wth a greater reducton for the Bg Creek systems) and a change n the hydrograph towards earler tmng of runoff. The change n the hydrograph s greater for the UARP system because of the lower elevaton of the basns where the system s located. Assocated wth the reducton n runoff there s a reducton n energy generaton n both systems. However, due to the greater change n the hydrologc condtons for the UARP system splls are greater n that system and hence the reducton n energy generaton (and assocated revenues) s greater as well. In both systems the ablty to meet peak hstorc power demands n the summer months would reman bascally unaltered. However, an ncrease n the occurrence of heat waves especally later n the summer perod (September) would ncrease peak power demand at tmes when these systems mght not be at peak power capacty unless operatng strateges are modfed. 6

8 1. Introducton As clmate change becomes more evdent there s an ncreasng nterest n determnng the mpacts that could happen on dfferent sectors of the economy. Calforna s water and hydropower energy resources are a vulnerable sector that has motvated a seres of recent research (Madan et al., 27, 28; Tanaka et al., 27; Vcuna et al., 26, 28). Hydropower consttutes around 15% of n state energy generaton n Calforna (Aspen Envronment and M- Cubed, 25) wth a greater value assocated wth ts use predomnantly durng on-peak perods. Half of ths energy generaton occurs at hgh elevaton (over 1, feet) n systems that have less storage capacty but hgher natural head compared to ther lower elevaton counterparts. A recent study by our research group estmated the mpacts of clmate change on the hgh elevaton Upper Amercan Rver Project (UARP) operated by Sacramento Muncpal Utltes Dstrct (SMUD). Ths system s located wthn the Rubcon and Upper Amercan Rver basns. The model used to smulate the operatons of the UARP system was run under four clmate change scenaros that were made avalable for the Frst Bennal Scence Report to the Calforna Clmate Acton Team, an ntatve of the Calforna EPA and Calforna Energy Commsson ( The results of that report ncludng the study developed by ths research group on the mpacts on the UARP system were publshed on a specal ssue of the Clmatc Change journal (Cayan et al. 28). In our current research presented n ths report, recognzng some of the lmtatons of our prevous work (Vcuna, et al. 26, 28), we have ntroduced three major modfcatons to the model developed to optmzed and smulate the hstorc and future operatons of the UARP system: 1. We modfed the objectve functon of the lnear programmng optmzaton routne by changng the energy prce representaton and by ncludng a value to water storage as a surrogate for power benefts. 2. We changed the analyss of nflow uncertanty n the model by consderng a more realstc forecast representaton. 3. We have modfed the approach used to determne future (clmate change) operatons. Ths new approach avods the use of perturbaton ratos to develop the future hydrologc scenaros by relyng nstead of the actual projectons of an hydrology model run usng the clmate change scenaros. Ths change allows the representaton of changes n clmate varablty as projected by clmate change scenaros. In addton to the study done on the UARP system, we have ntroduced a second case study, smulatng the operatons of the Bg Creek system operated by Southern Calforna Edson under both hstorc and clmate change hydrologc condtons. The Bg Creek system s located n the upper San Joaqun rver basn n the Southern Serra Nevada whereas the UARP system s located n Northern Serra Nevada. That condton plus some changes n the system confguraton wll allows obtanng a more complete pcture of the effects of clmate change on hgh elevaton hydropower n Calforna. The report s organzed as follows: 7

9 1. Frst the methodology used to estmate the mpacts of clmate change on the operatons of a hgh elevaton hydropower system s ntroduced 2. Then we ntroduce our two cases studes, the UARP and the SCE Bg Creek systems. 3. Then we present the analyss of the results assocated wth the hstorc and clmate change scenaros selected for ths work. 4. We fnsh wth some conclusons. 8

10 2. Methodologcal Approach The followng secton dscusses the new methodologcal approach used n ths work. The major steps nvolved n ths approach ncludes a calbraton frst of a smulaton model of the hstorc operatons and then the study of the effects of clmate change usng the calbrated smulaton model. 2.1 Smulaton of hstorc operatons To smulate the operatons of the hgh elevaton hydropower system we have constructed an optmzaton model that uses as nput a tme seres of hydrologc condtons at dfferent nflow locatons n the systems and that gves as output detal operatons of the system (reservor storage, reservor release through turbnes and though spllways or drectly to the rver) at the daly tme resoluton. Ths smulaton model s based on a sequental mult-step lnear programmng (LP) optmzaton routne that determnes daly operatons for the dfferent components of the hydropower system. Two possble objectve functon confguratons are consdered to run ths model. A frst case called the energy drven model, the objectve of the optmzaton routne s to maxmze energy generaton revenues, restrcted to operatonal constrants (e.g. mnmum nstream requrements), and physcal constrants, such as turbne or reservor capacty. Usng an approach developed n Madan et al. (27) we estmate energy revenues usng a contnuous pece-wse lnear representaton of energy prces derved from a dstrbuton of hourly CalIso prces specfc for each month. Fve segments are consdered n the lnearzaton for each month. Ths s consdered an mprovement of our prevous work whch ncluded only a sngle on and a sngle off peak energy prce (followng Gryger and Stednger (1985) and Trezos and Yeh (1987)) developed dong a percentle analyss of the Calforna PX data (Appendx A shows the comparson of the LP model formulatons under the two energy prce structure). The energy prce used s a functon of the percent tme turbnes are n operaton assumng they operate at maxmum capacty durng ths tme. Ths facltates the computatons reducng the number of varables needed (just percent tme s needed and not percent tme and assocated flow). System operatons of a hgh elevaton hydropower system are based on a varety of factors n addton to electrcty generaton, ncludng operatonal releases for peakng and real-tme load followng (SMUD, 21). The pure energy drven model smplfes these aspects by usng energy prces as a proxy for all other objectves. Based on the results obtaned wth ths energy drven model (presented later) and by dscussons we had wth UARP system operators we decded to nclude a new drver n the system operatons that took nto account the value of havng water stored n the reservors and the ablty to transfer ths stored water nto power capacty that could be used to match peak demand and spnnng operatons. We called the model wth ths new objectve functon the energy and storage drven model. The value gven to storage s dfferent for each month and could be potentally dfferent for all reservors (here though we have used the same value for all reservors). These monthly values were calbrated to accurately represent monthly hstorc operatons. Appendx B shows brefly the changes ntroduced n the objectve functon by ths new structure. The optmzaton routne s performed over a movng horzon of 12 months, smlar to the approach consdered by Hooper et al., (1991). Lmtng the model horzon to 12 months only 9

11 lmted the amount of hydrologc nformaton avalable and hence recreated partally the level of uncertanty perceved by real reservor operators. However f ths horzon s kept too short (say one month only) the operatons of the LP model, n order to maxmze profts, wll completely dran reservors by the end of the tmestep perod. The ncluson as part of the objectve functon of the remanng 11-months s needed to avod that myopc behavor. We could also avod ths dranage by addng an end-storage functon, but t s smpler and effectve to extend the tmestep perod by enough tme so that the zero end-storage does not affect storage at the end of the frst month. Ths movng horzon optmzaton approach s a compromse between a reasonable amount of hydrologc nformaton and smplcty n the objectve functon formulaton and wll be subject to more analyss n future developments of the model. The model developed n Vcuna et al. (28) has wthn these 12 months a complete knowledge of hydrologc condtons (perfect foresght) at dfferent temporal resolutons. The frst of these months was optmzed at a daly tme step and the remanng 11 months were modeled at monthly tme steps. The use of a daly tme step wthn the frst month allowed the assessment of sngle flood events, whch s crucal to the analyss of system operaton wth regard to undesred spllage. Only the output of the frst month was retaned; the results of the 11-month model results were dscarded and the next tme-step performed daly optmzaton of the second month. In order to better represent the level of foresght of future nflows that the model has (agan tryng to replcate the level of nformaton that has a real operator) we have made the followng changes to the modeled developed n Vcuna et al. (28): 1. We ncluded a smaller tme horzon for the daly optmzaton module that better reflects uncertantes assocated wth flood events. The dea was to reduce that foresght to a more reasonable level (5 days nstead of a whole month). 2. We reduced the amount of foresght the model s assumng n determne reservor releases. As mentoned before the model used to have at the monthly tmescale a perfect foresght of 11 months worth of future nflows. Durng the snowmelt season 2-3 months of nflows foresght s reasonable (e.g. f the operator s makng a decson n Aprl), however at some other months the only nformaton avalable for the reservor operator are average flows for a gven months (e.g. f the operator s makng a decson n October). Here we replcated ths level of knowledge by ntroducng a varable factor that weghs perfect and average nflows to fnally estmate the nflow condtons as s avalable for the LP model at any pont n tme. If we look at the LP model formulatons (Appendx C) we have that under the new confguraton, two thngs j j change as compared to the base formulaton. In the frst place dn, dlast are not necessary the frst and last day wthn a month but are nstead the correspondng ntal and fnal days of a seres of consequent segment of 5 days that would be used n the daly wndow of optmzaton. The second change s wth the mass balance equaton were now nstead of usng the perfect foresght nflow ( I n ) we use now a modfed tme seres of nflow condtons that s constructed n the followng way. 1

12 For a gven month m and year t. For n=1:5 (daly wndow of optmzaton) I n tmd,, = I (actual nflow condtons for year t, month m and day d) For n=6-17 (sub-monthly and monthly wndow of optmzaton) I n tm, ( s ) I m s = I * wm + *(1 wm) (weghted average of actual flows for a gven month and year and average nflow condtons for that partcular month). s The weghng factor wm s a functon of the ntal month of the tme seres (month s) and the month n whch we are dong the forecast. Ths factor changes over tme to reflect the better forecast of nflow condtons avalable at dfferent ponts n the year. For example w s m n October (month s) s equal to for all months to reflect a complete uncertan scenaro, whereas s wm when s s May would be close to 1 to months durng the snowmelt season (m=june, July, August, September) but then afterwards. Ths new formulaton represents more realstcally reservor operatons under uncertanty and offers a better test to assess the mpacts assocated wth clmate change, especally those related to the change n flood events frequency and magntude. 2.2 Development of future clmate change scenaros The optmzaton model ntroduced n the prevous secton wth ts new methodology accurately represents hstorc reservor operatons. Ths calbrated model s used to estmate the mpacts that clmate change could have on the followng detaled operatng varables: Mnmum stream flows: the model s used to determne how often mnmum stream flow requrements are controllng operatons n the system of reservor. In future studes ths requrements could be modfed to represent dfferent regulaton envronments. Outflow of the hgh elevaton system onto the valley floor. For example n the case of the UARP system, Folsom Reservor s located just downstream of the last reservor that composes ths UARP system, whch releases becomes the nflow condtons nto ths mportant pece of the Central Valley Project (CVP) system. The model smulates condtons at a daly level so t could be used for example to estmate future changes floodng condtons affectng the operatons of ths reservor that could affect the cty of Sacramento. Splls and other reservor operatng varables: A detaled model as ths one based on prncples such as water balance but consderng detal constrants and operatng characterstcs could be used to smulate changes n a set of dfferent relevant operatng varables. For example the model could be used to estmate power capacty (as compared to energy generaton) n crtcal summer months. 11

13 In order to represent changes n future hydrologc varablty we are usng nstead of a perturbaton rato approach (Vcuna et al., 27, Vcuna et al., 28) drect tme seres of hydrologc condtons as projected by the VIC hydrology model run by a gven clmate change scenaro. The dfference n these two approaches s shown n Appendx D. Usng an approach that not reles on the perturbaton ratos s benefcal because the effects of changes n the nter annual varablty of clmatologc and hydrologcal varables could be studed wth such approach (Purkey et al., 28). For the specfc mpacts assocated wth hydropower operatons usng a drect hydrology approach allows the exploraton of the transent and progressve effects of clmate change. Ths s crtcal to answer questons about when should operatons (or forecastng schemes) be altered base on the already vsble effects on the hydrologc condtons. All the above are the benefts of usng a detaled water based model such as the one developed n ths project. 12

14 3. Case Studes: Upper Amercan Rver Project and Bg Creek System The focus of ths project s the study the operatons under hstorc and clmate change hydrologc condtons of hgh elevaton hydropower systems usng an optmzaton model that ncludes detals about the system confguratons and constrants. As case studes of ths project we have selected two hgh elevaton systems n Calforna. One of them s the Upper Amercan Rver Project (UARP) located n the Upper Amercan and Rubcon basns (headwaters at 9,9 ft ( 3, m)) and operated by Sacramento Muncpal Utltes Dstrct (SMUD). The second case study s the Bg Creek system located n the upper San Joaqun basn (headwaters at 14, ft ( 4,2 m)) and operated by Southern Calforna Edson (SCE). A map showng the locaton of both systems s presented n Fgure 1. The UARP system was constructed between 1957 and It ncludes 11 reservors that can mpound over 425, acre-feet (ac-ft) of water, eght powerhouses that can generate up to 688 megawatts (MW) of power, and about 28 mles (45 km) of power tunnels/penstocks. The system s located above Central Valley Project (CVP) s Folsom Dam. Annual runoff to the UARP system s roughly 1, TAF. The project s currently n a FERC (Federal Energy Regulatory Commsson) relcensng stage, and thus suffcent data were publcly avalable to conduct the case study. The Project s composed of seven separate developments (a summary wth major characterstcs of these developments s shown n Table 1). The Bg Creek system s one of the largest and oldest hgh elevaton hydropower systems n Calforna, consstng of 9 power generaton plants for a total generaton capacty of approxmately 1, MW and about 54.3 mles (87.4 km) of power tunnels/penstocks. The Bg Creek system has a storage capacty of 56 thousand acre-ft (TAF) dstrbuted wthn 6 major reservors located wthn the upper San Joaqun rver watersheds. The system s located above Pacfc Gas&Electrc (PGE) s Kerckhoff reservor and hydropower staton and CVP s Mllerton Lake. Annual runoff to the Bg Creek system s roughly 1,8 TAF. Bg Creek System accounts for 9% of SCE s hydropower resources. The project s also under a FERC relcensng process. The Project s composed of nne separate developments (a summary wth major characterstcs of these developments s shown n Table 2). As can be seen from the data presented n both Tables 1 and 2 and above, the UARP and Bg Creek posses those typcal characterstcs of what have been normally domnated a hgh elevaton hydropower system (Aspen Envronment and M-Cubed, 25). Elevaton of the components n both cases are above 1, ft (hgher n the case of the Bg Creek). And n both cases the storage to runoff rato s relatvely small:.4 (425 TAF/1, TAF) and.3 (56 TAF/1,8 TAF) n the case of the UARP and Bg Creek systems respectvely. 13

15 Table 1. UARP system components ncluded n the model COMPONENT PARAMETER Loon Lake Robbs Peak Unon Valley Jones Fork Jaybrd Camno Whte Rock Elevaton (ft) 6,41 5,231 4,87 5,45 4,45 2,915 1,85 Head (ft) Reservor Capacty (TAF) Reservor depth (ft) Depth/Head 15% 6% 86% 9% 9% 7% 22% Penstock capacty (cfs) 999 1,249 1, ,344 2,99 3,948 Capacty (MW) Table 2. SCE system components ncluded n the model COMPONENT PARAME TER Portal PH Bg Creek No 1 Bg Creek No 2 Bg Creek No 2A Bg Creek No 3 Bg Creek No 4 Bg Creek No 8 Eastwood PS Mammoth Pool PH Elevaton (ft) 7,643/ 7,328 6,95 4,81 5,37 2,23 1,43 2,943 6,67 3,33 Head (ft) 23 2,131 1,858 2, ,338 1,1 Reservor Capacty 125/ (TAF) Reservor depth (ft) Depth/ Head 8% 4% 1% 3% 6% 13% 1% 3% 19% Penstock capacty ,265 3,437 1,35 2, (cfs) Capacty (MW)

16 UARP Formatted: Font: Palatno Lnotype, 12 pt Bg Creek Formatted: Font: (Default) Palatno Lnotype, 11 pt Fgure 1. Locaton of UARP and Bg Creek systems 15

17 4. Results 4.1 Hstorc operatons results and analyss of changes ntroduced To smulate hstorc operatons of the UARP and Bg Creek systems we used as nput tmeseres of daly nflows nto the set of reservors that compose both systems. In the case of the UARP system the tme perod covered was whereas n the case of the Bg Creek system the perod covered was The nter annual varablty of hydrologc condtons n both the UARP and Bg Creek systems s shown n Fgure 2 showng the smlar pattern but dfferent magntude of annual runoff n both systems. Annual Inflows (TAF) UARP SCE Fgure 2. Annual runoff nto the UARP and Bg Creek systems. The hstorc operatons for both systems were smulated usng the LP optmzaton routng explaned n Secton 2 of ths report. As explaned before we have consdered two dfferent objectves to determne these operatons. On one case the objectve functon consders only energy generaton revenues (we call ths the energy drven model) and the other we consder both energy revenues and storage value (we call ths the energy and storage drven model). Two exemplfy the dfferences between these two alternatve confguratons we present a summary of the UARP system s operatons n the followng set of fgures. We frst pay attenton to the results on energy generaton were we compare the results wth hstorc condtons. Fgure Fgures 3 and 4 show the comparson between energy generaton on an annual bass and on a monthly bass (as a percent of total generaton) for three cases: Actual hstorc Modeled hstorc under the energy drven model Modeled hstorc under the energy revenues and storage value drvers. 1 These data sets were provded by SMUD and SCE respectvely. 16

18 In the Fgure 3 showng the monthly pattern of generaton we have ncluded as well the results n energy patterns from a energy storage model consdered n the comparatve study presented n Madan et al. (27) and the monthly average energy prces. In Fgures 5, 6 and 7 we show average monthly and annual splls and average monthly end of month storage for all reservors respectvely comparng the two structures of objectve formulatons. Monthly percent Generaton 14% 12% 1% 8% 6% 4% 2% Energy prce ($/MWh) % Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Hst Generaton Generaton Energy Drven Generaton Energy and Storage Drven Generaton Madan Kaveh et et alal. (27) Average energy prces Formatted: Font: Tmes New Roman Fgure 3. Comparson between hstorc and modeled monthly percent energy generaton n the UARP system 35 Annual Generaton (GWh/year) Hst Generaton Generaton Energy Drven Generaton Energy and Storage Drven Fgure 4. Comparson between hstorc and modeled annual energy generaton n the UARP system 17

19 As can be seen from the results shown n Fgure 3 the model drven purely by energy revenues s not representng accurately energy generaton (the only varables avalable for comparson) at both the annual scale (model over predcts generaton) and at the monthly scale (where there s too much generaton n the wnter months and too lttle n the sprng months). The generaton pattern follows a pattern that s close to average energy prces (also shown n the Fgure), so t seems that operatons are not purely drven by ths varable. A system that s drven purely by energy prces and mportantly wth a fxed head (as we have set t up here for our LP confguraton) has lttle ncentve to fll up the reservors. So t tres to keep them as empty as possble ganng always from the releases made and the energy beng generated. Wth a closeto-empty reservor s much easer to handle splls whch are reduced n most of years to just comply to mnmum stream flow requrements (see Fgures 5 and 6 for the energy drven case) (remember that here splls consders all flows not passng through turbnes so ncludes stream flow requrements). Wth a reducton n splls water passng through turbnes s enhanced and so energy generaton s hgher than at the hstorc condtons. Includng a value for storage for dfferent months n order to represent objectves other than energy revenues clearly mproves the results. By addng ths value, reservor storage ncreases (compare two scenaros n Fgure 7) nducng a relatve hgher amount of splls (Fgures 5 and 6), reducng energy generaton (Fgure 4) and shftng generaton to months wthout a relatve hgher energy prce (especally sprng months). There s stll a slght over predcton n generaton whch s probably due to: an under predcton of splls (attrbuted to a better predcton of flows and the dampng effect of consderng a tme resoluton of daly nstead of hourly for example) an over estmate of the generaton capacty of the power plants especally n the generaton effcency. Monthly Average splls (cfs) Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Modeled Splls Energy Drven Modeled Splls Energy and Storage Drven Fgure 5. Average monthly splls (TAF) n the UARP system 18

20 Annual total splls (TAF) Modeled Splls Energy Drven Modeled Splls Energy and Storage Drven Fgure 6. Annual splls (TAF) n the UARP system Storage (TAF) Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Storage Energy Drven Model Storage Energy and Storage Drven Model Capacty Fgure 7. Average end of month storage for the whole system (TAF) n the UARP system In the case of the Bg Creek system smulatons we also consdered a storage value as part of the LP objectve functon. After calbratng ths storage value we obtaned operatons that agreed greatly wth the hstorc operatons of ths system as can be seen n Fgures 8 and 9. In these Fgures we compare monthly average and annual energy generaton of the SCE system. 19

21 Monthly percent Generaton 16% 14% 12% 1% 8% 6% 4% 2% % Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Hst Generaton Generaton Energy and Storage Drven Fgure 8. Comparson between hstorc and modeled monthly percent energy generaton n the Bg Creek system Annual Generaton (GWh/year) Hst Generaton Generaton Energy and Storage Drven Fgure 9. Comparson between hstorc and modeled annual energy generaton n the SCE system 2

22 4.2 Clmate change results The 28 Clmate Change Impacts Assessment s n charge of provdng the clmate change scenaros to be used n the studes that are part of the Second Bennal Scence Report to the Calforna Clmate Acton Team. A descrpton of the ntatve and the work done to make avalable the set of clmate scenaros can be found n the group s webste ( General Crculaton Model (GCM) output data was statstcally downscaled usng two approaches: the Bas Correcton and Spatal Downscalng (BCSD) approach and a Constructed Analogues (CA) downscalng approach. A comparson of both methods can be found n Maurer and Hdalgo (28). The CA requres GCM output that was not avalable for all scenaros consdered n the project. In order to nclude the largest possble arrange of scenaros we have chosen to use the BCSD downscaled datasets. All the scenaros used n ths work (lsted n Table 1) were prevously run through the VIC 2 hydrology model. From the set of grds that span the spatal resoluton of VIC n the Serra Nevada we selected a subset that completely enclosed the boundares of the UARP and Bg Creek systems watersheds. We followed by usng the methodology explaned n the prevous chapter (and n more detal n Appendx D) to develop tmeseres of future hydrologc condtons for the two systems for each one of the clmate change scenaros. Table 1. Clmate change scenaros used n the analyss GCM Emsson scenaros 3 CNRMCM3 B1 A2 GFDL CM21 B1 A2 NCAR PCM1 B1 A2 MIROC32MED B1 A2 MPIECHAM5 B1 A2 NCARCCSM3 B1 A2 2. The varable nfltraton capacty (VIC) model s a macroscale, dstrbuted, physcally based hydrologc model that balances both surface energy and water over a grd mesh, and has been successfully appled at resolutons rangng from a fracton of a degree to several degrees lattude by longtude. A descrpton of VIC can be found n Cayan et al. (26). 3. A2 and B1 are two of the future carbon emssons scenaros developed by the Intergovernmental Panel on Clmate Change n ts Specal Report on Emssons Scenaros (SRES). A2 reflects a future wth relatvely hgh carbon emssons, whle B1 reflects a future wth lower CO 2 emssons. These clmate change scenaros consdered n ths study were selected n an attempt to bracket the uncertanty exstng among models on Calforna clmate change clmatc predctons. A descrpton of the scenaros used n ths work can be found n (ref when avalable). A descrpton of the hydrologc model VIC can be found n (Njssen, et al., 1997). 21

23 Table 2 summarzes the man characterstcs of the scenaros developed by comparng the followng metrcs for three dfferent perods: Hstorc ( ) as represented by the clmate change scenaro; Early 21 st century (211-24); Md 21 st century (241-27); Late 21 st century (271-21). To smplfy the presentaton we show the average of the absolute value for the hstorc perod and the dfferent clmate scenaros for the dfferent varables. To show the change for later perods we show both the average and range of the relatve comparsons for the dfferent scenaros. The results are shown for the hydrology of the UARP and the Bg Creek system separately. Average annual nflow Average March through September (typcal snowmelt season) percent of annual nflow Average December through February 9 th percentle flows (ndcatng floods occurrng durng wnter months) The hydrologc scenaros showed n the Table present us wth the followng future condtons: Consstent wth prevous works done n Calforna there s clearly uncertanty n terms of the overall amount of water that could be flowng through the system. For both systems we see that average annual nflow s slghtly decreasng for the early part of the century for the average condtons for the scenaros projectons; by md century ths reducton n nflows s more obvous and n the case of the UARP system t s projected by almost all scenaros (wth just one showng just a slght ncrease n nflows; by end of the century the uncertanty s stll very large (specally for the Bg Creek System) and the magntude of the nflow reducton s even larger when takng the scenaros n average. Another mportant observaton to make wth regards to the change n the amount of water flowng through these systems s that the projectons show much larger reductons n the Bg Creek system than on the UARP system. Ths s a consstent result wth the projected changes n clmatc condtons n Northern and Southern Calforna (reference when avalable) In terms of the tmng of nflows there s a clear reducton of the snowmelt season runoff consstent wth the noton that ncreasng temperatures modfy the tmng of streamflow towards earler n the water year (Vcuna and Dracup, 27). All the scenaros and for all tme perods we see ths trend (wth the excepton of one scenaro n the early 21 st century for the UARP system whch shows a slght ncrease n snowmelt season runoff as a percent of annual runoff). Ths can be verfed by lookng Fgure 1 were we present average monthly runoff for both systems and the four dfferent tme perod. Agan we see that, although the drecton of ths trend s the same n both systems, the magntude of the change s larger n the UARP system than n the Bg Creek system. In the case of the UARP system and consderng the results n average we have that hstorcal hydrologc condtons represent that almost 7% of runoff flows durng the typcal snowmelt season. Ths number s reduced by more than 2% n average for all scenaros. So future hydrologc condtons n the basns feedng the UARP system show that around 55% of runoff occurs durng the months from March through September. The 22

24 condtons for the Bg Creek system n contrast show that the snowmelt season runoff represents almost 9% of annual runoff under hstorc condtons and that number s reduced to slghtly above 75% under future (end of century) projectons. Interestng to note that that number s stll above current condtons for the UARP system. Consderng that there are not sgnfcant dfferences n temperature projectons for both regons, ths dfference n hydrologc pattern can be attrbuted only to the dfference n elevaton of both systems (the Southern Serra Nevada Mountans beng hgher than the Northern counterparts). Ths has been a typcal result for studes done n Calforna n terms of dfferences n the sensblty of the two regons for the changes n temperature levels. And fnally n average all scenaros show an ncrease trend n extreme flows durng the wnter months. Ths s an expected result assocated wth the projectons n temperature ncrease but that could be compensated n some cases wth a reducton n precptaton and runoff. That s why n some of the scenaros there s a reducton n wnter extreme flows. By the end of the century however, even wth the largest reductons n flows that are projected by that tme the ncrease n temperature s enough to ncrease extreme runoff n all scenaros. It s nterestng to note that the Bg Creek system has under hstorc condtons smaller extreme flows durng the wnter months although t has a larger amount of water flowng through the system as compared to the UARP system. But ths system also experences a larger ncrease n these flows under the projected future scenaros. It s expected that ths ncrease n extreme flows for both systems could dffcult ther operatons durng wnter months and ncrease the amount of undesred splls occurrng. 3 Average Monthly Runoff (m /s) Hstorc Early 21st Century Md 21st Century Late 21st Century Hstorc Early 21st Century Md 21st Century Late 21st Century O N D J F M A M J J A S O N D J F M A M J J A S Fgure 1. Changes n monthly hydrologc condtons n UARP and Bg Creek systems 23

25 Table 2. Comparson of hydrologc condtons for dfferent tme perods and the two hydropower systems consdered n ths study (absolute value for hstorcal perod and average plus range n percentage change for future perods) Varable Perod UARP System System Bg Creek System Annual Runoff n TAF (mll m 3 ) Percent runoff durng snowmelt season (%) Average 9th percentle runoff durng wnter months n cfs (m 3 /s) Hst 1,4 (1,238) 1,88 (2,229) Early -.3 % (-22 % / 21.6 %) -1 % (-25.6 % / 21.8 %) Md -9.3 % (-34.9 % /.6 %) % (-49.3 % / 8.9 %) Late -1.1 % (-24.5 % / 16.4 %) % (-39.9 % / 21.3 %) Hst 68.9% 87.8% Early -8 % (-16.2 % /.3 %) -3.4 % (-7 % / -.1 %) Md -9.5 % (-15.1 % / -1.4 %) -6.4 % (-12.1 % / -1.2 %) Late % (-32.9 % / %) % (-28.5 % / -6.3 %) Hst 1214 (34) 74 (2) Early 12.4 % (-7.1 % / 36.2 %) 24.1 % (-3.7 % / 6.5 %) Md 7.5 % (-1.9 % / 31.5 %) 25.9 % (-18.3 % / 61 %) Late 24.1 % (1.4 % / 53.7 %) 7.7 % (15.3 % / %) To present the mpacts that these clmate change scenaros could have on the operatons of the UARP and Bg Creek systems we have the selected the followng key varables: Annual and Monthly Energy Generaton Average August system capacty (a measure of the ablty of the system to meet peak demands by the end of summer) Annual and Monthly Spllage Downstream release (to Folsom and Mllerton dams) A Table summarzng the output for all scenaros and all tme perods s presented as follows. The format of presentaton s smlar to the case were we show the projected hydrologc condtons. For each of the varables consdered we show frst the average value for the hstorc perod and then for each of the future tme perods we show the average change (percent change from hstorc condtons) and the range consderng the results from all scenaros. 24

26 Table 3. Comparson of dfferent system outputs for dfferent tme perods and the two hydropower systems consdered n ths study (absolute value for hstorcal perod and average plus range n percentage change for future perods) Varable Perod UARP System System Bg Creek System Hst 1,976 3,58 Energy Generaton n GWh/year Energy Generaton revenues n mll $/year Average August Power Capacty n MW Average Splls n cfs (m 3 /s) Early 2.1 % ( 19.9 % / 14.9 %).6 % ( 14.2 % / 23.2 %) Md 8.2 % ( 31.3 % /.2 %) 8 % ( 38 % / 3.3 %) Late 12.2 % ( 25.1 % / 7 %) 1.4 % ( 26.8 % / 17.4 %) Hst Early 1.3 % ( 14.5 % / 1.8 %).7 % ( 11.3 % / 26.4 %) Md 5.8 % ( 23.1 % / 2.2 %) 4.7 % ( 33 % / 9.6 %) Late 8.5 % ( 18.5 % / 5.2 %) 7.8 % ( 23.4 % / 17.2 %) Hst 654 1,34 Early.2 % (.6 % /.1 %).1 % (.2 % / %) Md.2 % (.6 % /.3 %).1 % (.3 % /.1 %) Late.1 % (.6 % /.2 %).2 % (.6 % /.1 %) Hst 269 (8) 3,447 (98) Early 19.2 % ( 43.4 % / 96.1 %).5 % ( 31.9 % / 26.5 %) Md 1.8 % ( 59.5 % / 49.5 %) 17.3 % ( 56.1 % / 13.1 %) Late 1.8 % ( 27.2 % / 14.5 %) 21.8 % ( 48.3 % / 25 %) Several conclusons can be derved from the results presented n Table 3. Frst we can see that n average there s a reducton n the energy generaton and the assocated revenues that can be obtaned from the operaton of these systems. There s however a large uncertanty n the results wth some scenaros showng an ncrease n energy generaton benefts. Ths uncertanty s smaller at md century where most scenaros show a reducton n benefts. Smlarly to the conclusons derved n Vcuna et al. (28) we can see also that the reducton n revenues s smaller than the reducton n energy generaton. Ths s explaned by the fact that wth a 25

27 reducton n flows there s larger storage capacty avalable n the system to move the water to when t s more valuable (e.g. summer months). To further understand the mpacts that changes n the hydrologc condtons have on the operatons of these systems we have produced a seres of addtonal fgures. Frst n Fgure 11 we compare for all scenaros but just the last tme perod (late 21 st century) the changes (as compared to hstorc values) n annual system runoff wth annual changes n annual energy generaton and annual revenues. In the chart we have also ncluded the best ft lnear relaton for all four data sets wth the man propertes of these relatonshps presented n Table 4. The fgure shows a seres of nterestng results. Frst we corroborate here that there s a clear relaton between changes n energy generaton and revenues and changes n system runoff. The R 2 of the lnear correlatons for the four data sets presented n ths chart s above.92 for all cases. So n all four cases the change n annual runoff s a large predctor of the change n system energy generaton and revenues assocated. And the sgn of the coeffcent of ths varable clearly shows that as annual runoff s reduced energy generaton and revenues are reduced as well. It s nterestng though to note here some subtletes n these asseveratons. Frst we see that for both systems the coeffcent for the relaton between energy generaton and runoff s greater than the coeffcent for the relaton wth revenues and runoff. Ths shows agan as expressed earler the ablty of the system operatons to move water throughout the year to ncrease the ablty to generate at tmes when energy s more valuable. We see also that the coeffcents for the UARP system are smaller than the coeffcents for the SCE system for both types of relatons. Ths means that for a gven change n annual runoff the UARP system has assocated a larger reducton n annual generaton and revenues than the Bg Creek system. Ths result s attrbuted to the fact that the hydrologc changes (n terms of pattern changes) n the UARP system are larger than those affectng the Bg Creek system as was already mentoned. The projected hydrology n the UARP system s more nconvenent wth more water flowng n months when t s not needed (wnter months) and less when t s needed (late sprng and summer months). 26

28 Change n annual energy generaton and revenues (%) Change n annual runoff (%) SCE Energy vs Inflows SCE Dollar vs Inflows UARP Energy vs Inflows UARP Dollar vs Inflows Fgure 11. Comparson between changes n hydrologc condtons and UARP and Bg Creek systems outputs Table 4. Summary of lnear correlatons between changes n annual runoff and system outputs Varable UARP System Bg Creek System Energy vs Runoff Revenues vs Runoff Energy vs Runoff Revenues vs Runoff R Coeffcent

29 Average Monthly Release (cfs) Changes n Reservor Release Hstorc Early 21st Century Late 21st Century Average Monthly Release (cfs) Changes n Reservor Release Hstorc Early 21st Century Late 21st Century Average Monthly Splls (cfs) O N D J F M A M J J A S Changes n Reservor Splls Hstorc Early 21st Century Late 21st Century O N D J F M A M J J A S Changes n Storage Average Monthly Splls (cfs) O N D J F M A M J J A S Changes n Reservor Splls Hstorc Early 21st Century Late 21st Century O N D J F M A M J J A S Changes n Storage Average Monthly Storage (TAF) Hstorc Early 21st Century Late 21st Century System Capacty Average Monthly Storage (TAF) Hstorc Early 21st Century Late 21st Century System Capacty O N D J F M A M J J A S O N D J F M A M J J A S Fgure 12. Summary of UARP and Bg Creel system s operatons under three dfferent tme perods 28

30 The nconvenence of ths projected hydrology s evdenced wth changes n the system operatons that can be verfed n the charts presented n Fgure 12. In these charts we compare three man systems operaton varables: reservor release through turbnes, splls and storage at the monthly level for three dfferent tme perods (hstorc, early and late 21 st century). The charts presented show that both systems have a comparable tmng of reservor release through turbnes wth the excepton that they tend to be larger n early sprng months n the UARP case. However, the tmng of splls s clearly dfferent n both systems. Under hstorc condtons splls durng wnter months are qute larger n the UARP system than n the Bg Creek system, the latter havng most of ther splls occurrng concentrated durng the sprng and summer months. Ths dfference s even larger under the clmate scenaros especally by the end of the century were the UARP now experences the most of the occurrence of splls durng the wnter months but the Bg Creel system stll has them concentrated durng the sprng and summer months and at a smaller magntude than under hstorcal condtons. So n the case of the UARP system, the larger change n tmng of runoff ncreases the occurrence of splls n wnter months and that explans the reason why there s a larger reducton n energy generaton and revenues. It also nterestng to note now gong back to Fgure 11 that ths change n tmng of runoff affects UARP system operatons n a way that n the future an ncrease n runoff has assocated a smaller (n a relatve sense) ncrease n revenues. Than can be checked by lookng that for those scenaros that have an ncrease n runoff n the UARP system the dots representng the changes n outputs s below the 45º lne meanng the change n smaller n a relatve sense. We see also that the lnear relaton between revenues and runoff n ths system s weaker than the relaton between energy generaton and runoff n ths system. The dfference between the coeffcents of those relatons (see Table 4) s larger than the dfference exstng n the case of the Bg Creek system. In the case of the Bg Creek system we have that for most scenaros wth the excepton of the drest one the ncrease n revenues s larger than the ncrease n runoff. Fnally we can see that reservor storage s kept at smlar levels under all dfferent tme perods. The mpacts of clmate change n both systems are reflected by an ncrease n storage durng the late wnter and early sprng months and slght reducton durng the late sprng and summer months. Ths last reducton s more evdent n the case of the Bg Creek system due to the larger reducton n runoff as projected for ths system. These results reflect the great flexblty that a hgh elevaton hydropower system has n managng ther reservor nflows. Not havng flood control rules attached to ther management operatons allowed these systems to deal very effectvely wth changng nflow condtons by change the tmng reservors are beng reflled and empted. Wth regards to the capacty of these hydropower systems to generate energy when the demand s at ts peak levels (summer months) we can see that the new hydrologc condtons bascally reman unaltered ths capacty. The average system power capacty n August s reduced at the most n.6%. A reason behnd ths nsenstvty s that t has to be kept n mnd that these hgh elevaton systems have a large proporton of ther head avalable fxed (use the gradent n the terran as avalable head) ndependent of storage at the reservors. The results presented are only for the month of August whch typcally has the largest load for energy n Calforna. Ths demand s hghly determned by the occurrence of extreme hot days or heat waves (Mller et al., 28). An ncrease n temperature levels should ncrease the occurrence of extreme hot days n several regons n Calforna and thus affect the energy load demand (Mller et al., 28; Hayhoe et al., 24). One of the effects of these changes n terms of the operaton of a hgh elevaton 29

31 hydropower system could be an extenson of the number of months when the load s at maxmum levels. The effect that ths could have on both the UARP and Bg Creek systems s shown n Fgure 13. In ths Fgure we present a comparson of the percent tme (number of days) wthn a month that temperature levels ndcate the occurrence of a heat wave (defned as a day wth temperatures above hstorc 95 th percentle, ref when avalable) and the percent tme where system power capacty (s above the 99% percent level). Ths nformaton s presented for four cases: hstorc and late 21 st century for the UARP and Bg Creek systems. For each one of these cases we present the analyss for the months from May tll September and n each case we show the average for all 12 scenaros but also the range n the condtons. It can be shown n ths Fgure that both systems operatng accordng to hstorc objectves (hstorc energy prces and peak demand) shouldn t have problems supply energy at tme wth peak demand from May untl July. In August and especally n September we see that the Bg Creek system would face a stuaton where the number of days wth head waves n the future wll exceed the number of days the system s at peak capacty. The UARP system s expected to have fewer problems than the Bg Creek system meetng ths change n peak demand capacty n August. In September we see though that the range of heat waves percentage overlaps the range of peak system capacty. Based on these results we can conclude that these two systems shouldn t have problems meetng peak power demands n the late sprng and early summer months even wth an ncrease n power demand assocated wth ncreased occurrence of heat waves. However, f there s an ncrease n heat waves latter n the summer, these two systems (especally the Bg Creek system) would have trouble meetng peak demand unless keepng extra water stored n reservors and hence reducng even further the amount of energy beng generated (due to ncreased splls) a. Bg Creek/Los Angeles Hstorc b. Bg Creek/Los Angeles Late 21 st Century Formatted: Font: Tmes New Roman, 1 pt, Italc Formatted: Font: Tmes New Roman, 1 pt, Italc MAY JUN JUL AUG SEP Ocurrence of heat waves (%) System at peak power capacty (%) MAY JUN JUL AUG SEP Ocurrence of heat waves (%) System at peak power capacty (%) c. UARP/Sacramento Hstorc d. UARP/Sacramento Late 21 st Century Formatted: Font: Tmes New Roman, 1 pt, Italc Formatted: Font: Tmes New Roman, 1 pt, Italc MAY JUN JUL AUG SEP Ocurrence of heat waves (%) System at peak power capacty (%) MAY JUN JUL AUG SEP Ocurrence of heat waves (%) System at peak power capacty (%) Fgure 13. Comparson between occurrence of heat waves and system at peak capacty 3