Modeling the Boise Reservoir System with Climate Change Leslie Stillwater, Pacific NW Region

Reclamation’s Boise Project The Boise Project provides water to lands in southwestern Idaho and eastern Oregon Boise Basin Project Reservoirs, active capacities: Anderson Ranch, 413 kAF Arrowrock, 272 kAF LuckyPeak (COE facility), 264 kAF Lake Lowell, 159 kAF Irrigated Lands: 224,000 acres primary supply 173,000 acres supplemental supply

Warmer Temperatures Less Snowpack More Precipitation (some say) Greater variability in flows Earlier runoff Higher winter flows; lower summer flows Climate Change Is Likely to Bring…

Preliminary Assessment Questions will Reclamation meet it’s current contractual obligations for water storage and delivery? will Reclamation meet it’s environmental obligations? will current flood risk management practices be adequate?

The IPCC is a scientific intergovernmental body set up by the World Meteorological Organization (WMO) and by the United Nations Environment Programme (UNEP). The IPCC is a scientific intergovernmental body set up by the World Meteorological Organization (WMO) and by the United Nations Environment Programme (UNEP). The IPCC provides an objective and neutral source of information about climate change. The IPCC provides an objective and neutral source of information about climate change. The IPCC does not conduct research nor does it monitor climate related data or parameters. The IPCC does not conduct research nor does it monitor climate related data or parameters. Intergovernmental Panel on Climate Change (IPCC)

Selected IPCC Model Output Three projection scenarios for the year 2040 were selected from among the suite of IPCC models. Each applies an aggressive emissions scenario, assuming increasing emissions based on population growth and current technological and economic trends. ECHAM ECHAM developed by the Max Planck Institute for Meteorology, Germanydeveloped by the Max Planck Institute for Meteorology, Germany Echam simulations produce moderate temperature and precipitation trends when compared to other IPCC models.Echam simulations produce moderate temperature and precipitation trends when compared to other IPCC models. IPSL IPSL developed by the IPSL Institut Pierre Simon Laplace, France.developed by the IPSL Institut Pierre Simon Laplace, France. IPSL simulations produce the greatest warming and increased precipitation trends.IPSL simulations produce the greatest warming and increased precipitation trends. GISS GISS developed by NASA / Goddard Institute for Space Studies, USAdeveloped by NASA / Goddard Institute for Space Studies, USA GISS simulations produce the lowest warming trends and a small decrease in precipitation.GISS simulations produce the lowest warming trends and a small decrease in precipitation.

Selected IPCC Model Output Modeled Predictions for the Year 2040

6 Scenarios were developed from 3 Climate Change Projections for Year 2040 Echam - Temp Adjustments Only Echam - Temp Adjustments Only Echam - Temp and Precip Adjustments Echam - Temp and Precip Adjustments GISS - Temp Adjustments Only GISS - Temp Adjustments Only GISS - Temp and Precip Adjustments GISS - Temp and Precip Adjustments IPSL - Temp Adjustments Only IPSL - Temp Adjustments Only IPSL - Temp and Precip Adjustments IPSL - Temp and Precip Adjustments

Climate Impacts Group (CIG) The projected precipitation and temperature changes were downscaled to the Pacific Northwest by the Joint Institute for the Study of Atmosphere and Oceans Climate Impacts Group (CIG) at the University of Washington.

How Climate Affected Naturalized Streamflows were Developed T and P Adjustments were obtained from the Climate Impacts Group for each Climate Scenario T and P Adjustments were applied to the National Weather Service River Forecast System model (NWSRFS) to produce daily local naturalized streamflows (WY )

NWSRFS Model Forecasts streamflow Forecasts streamflow Collection of hydrologic/hydraulic models calibrated to observed snow, soil moisture, river, and reservoir conditions and historical meteorological data Collection of hydrologic/hydraulic models calibrated to observed snow, soil moisture, river, and reservoir conditions and historical meteorological data Model input (for this study): T and P Model input (for this study): T and P Model components: Model components: Sacramento Soil Moisture Accounting ModelSacramento Soil Moisture Accounting Model SNOW-17SNOW-17

NWSRFS Concepts

NWSRFS Concepts

Daily Naturalized Flows at Lucky Peak using Temperature Predictions for 2040 (NWSRFS model results)

Daily Naturalized Flows at Lucky Peak using Temperature and Precipitation Predictions for 2040 (NWSRFS model results)

How Climate Affected Streamflows were applied in the Planning and Operations Models Naturalized streamflows from each NWSRFS Climate Scenario were compared to the unadjusted NWSRFS Scenario (calibrated to historic streamflows) to produce daily local naturalized streamflow adjustments The daily streamflow adjustments were applied to the Monthly Planning Model (Snake River Revised MODSIM Model) The daily streamflow adjustments were also applied to the Daily Boise Operations Model (MODSIM)

Model Purposes and Assumptions The monthly planning model addresses storage, Reclamation contract obligations, water rights, irrigation deliveries and minimum streamflows –Modeled irrigation deliveries are based on present level delivery requirements –Environmental obligations are based on current practices The daily operations model addresses flood risk management and refill

Results (page1) The ability to refill Project reservoirs may not be significantly impacted by Climate Change, but refill is dependent on the successful response to changing flood risks Project deliveries are likely to not be significantly affected by Climate Change (natural flow diversions decline, Project storage deliveries increase) Environmental obligations for storage and streamflows are likely to not be significantly affected by Climate Change

Planning Study: Modeled Diversions Temperature Adjustments Only

Planning Study: Modeled Diversions Temperature and Precipitation Adjustments

Planning Study: Modeled Refill Temperature Adjustments Only

Planning Study: Modeled Refill Temperature and Precipitation Adjustments

Results (page2) However, winter and spring flooding and flood control operations are more likely with Climate Change and will be the major issue in the Treasure Valley Flood risk management and reservoir refill go hand-in-hand

Observations on Flood Risk Management and Reservoir Refill (page1) Current COE regulations, guidelines and space requirements are outdated, having been developed using data from 1895 through Starting about 1980, the guidelines under-predict inflows prior to April 1 and over-predict inflows after April 1 With Climate Change, the under- and over- predictions are even larger

Observations on Flood Risk Management and Reservoir Refill (page2) Accurate forecasts will become more difficult develop to due to the influences of precipitation on the basin and increased flow variability

Boise Project Flood Operations Starting on January 1, a volume forecast from ‘now’ until the end of July is developed Part of that forecast will arrive April – July producing the April 1 space requirements (rule curves) The remainder of that forecast will arrive ‘now’ – March determining the rate of release to get down to the April 1 space requirements Measure of success is discharge < 7,000 cfs at Glenwood Bridge

No Adjustment 1970/1971 Apr 1 Space (AF) required = 950,150 achieved = 885,780

Echam T 1970/1971 Apr 1 Space (AF) required = 664,530 achieved = 663,780

Giss T 1970/1971 Apr 1 Space (AF) required = 822,790 achieved = 820,390

Ipsl T 1970/1971 Apr 1 Space (AF) required = 588,970 achieved = 582,100

Echam TP 1970/1971 Apr 1 Space (AF) required = 784,410 achieved = 613,210

Giss TP 1970/1971 Apr 1 Space (AF) required = 834,650 achieved = 831,930

Ipsl TP 1970/1971 Apr 1 Space (AF) required = 852,310 achieved = 244,280

No Adjustment 1970/1971 Apr 1 Space (AF) required = 950,150 achieved = 885,780

Impacts to Reservoir Refill Refill capabilities go hand-in-hand with flood control operations When modeled, perfect forecasts (!) and revised operating rules produce excellent refill capability in all Climate Change Scenarios studied

So, will Reservoirs fill? Streamflow forecasts will need to be early – that seems unlikely Greater streamflow variability produces greater uncertainties in streamflow forecasts Operators will be hesitant to draw down early and start an early fill

So, will there be flooding in Boise? Most likely* *given our current assumptions

Comments on the Daily Operations Studies Assumptions drive the study results –A2 IPCC scenarios (aggressive emissions) –T and P results are scalable to PN Region and to the Boise Basin –Starting storage conditions of Nov 2001 (historic median) –Perfect forecasts We addressed uncertainties by employing results from a range of IPCC models

Daily Operations Study Results Reliable forecasts will be even more critical Early forecasts (prior to Jan 1) will be required Drawdown needs to start before Jan 1 Space requirements need to start earlier than Apr 1 Maintaining 55% space in Lucky Peak and Arrowrock may not be possible Glenwood Bridge discharge Jan – Apr will be higher Glenwood Bridge discharge > 7,000 cfs can be anticipated if the wettest scenario is realized

Web sites Hydromet teacup diagrams: – Intergovernmental Panel on Climate Change – NWS models – Climate Impacts Group, U of Washington –