Mid-Range Streamflow Forecasts for Water Supply Management in the Puget Sound Region Matthew Wiley Richard Palmer October 26, 2005

Water Resources Management and Drought Planning Group The Climate Impacts Group PRISM, Puget Sound Regional Synthesis Model

Seattle Public Utilities Tacoma Water Everett Public Utilities Partner Utilities: Central Puget Sound Water Supplier’s Forum

Outline Forecast Method and Locations Some Past Results What lies ahead…. New forecast products in the works

Mid-Range Forecasts for Utilities in the Puget Sound Using DHSVM  1-9 month lead time forecasts of streamflows  For Puget Sound area water supply systems. Forecasts are based on:  Current watershed conditions  ENSO state conditioned ESP simulations  CPC’s long-lead seasonal forecast.

Hydrologic Model - DHSVM Physically based, distributed model Calculates energy and water balance at the grid cell level. 150 meter resolution, 3hr time-step Station based meteorology Output streamflows are aggregated to monthly total volume. Recently incorporated an experimental groundwater component.

Sultan River  Snohomish PUD Hydropower project  Everett Water Supply S.F. Tolt River  Seattle Water Supply Cedar River  Seattle Water Supply Green River  Flood Control  Tacoma Water Supply All have some degree of instream flow requirements for salmon habitat preservation

Reading the forecast graphs

Last Spring’s Forecast March 2005 Forecast: Cedar River, above Chester Morse Reservoir

Conclusions from March 2005 Forecast Meeting: A 10% reduction in consumption reduces probability to around 5% chance of shortfall Current snowpack is only half of the picture, spring rains can also refill reservoirs inches* (at Seatac) between March 1 and July 1 will get us to near average storage by September 1 * (Average precip is 9.5 inches)

Retrospective: September04, Cedar River above Chester Morse 9 month lead: May forecast for a little below average

Retrospective: October04, Cedar River above Chester Morse 8 month lead: May forecast for a little below average

Retrospective: November04, Cedar River above Chester Morse 7 month lead: May forecast below average, June, July average

Retrospective: December04, Cedar River above Chester Morse 6 month lead: May forecast furthur below average, June, July average

Retrospective: January05, Cedar River above Chester Morse 5 month lead: May and June forecast below average, July average

Retrospective: February05, Cedar River above Chester Morse 4 month lead: May, June, July forecast below average

Retrospective: March05, Cedar River above Chester Morse 3 month lead: May, June, July forecast below average

Retrospective: April05, Cedar River above Chester Morse 2 month lead: May, June, July forecast below average

Retrospective: May05, Cedar River above Chester Morse 1 month lead: May, June, July forecast below average

Retrospective: June05, Cedar River above Chester Morse 0 month lead: Model hits flows well when given observed weather

Predicting Spring flows Benefit of climate information over full historic range is apparent immediately. Accuracy continues to improve as lead time decreases

Retrospective: July05, Cedar River above Chester Morse Start looking to fall…

Retrospective: August05, Cedar River above Chester Morse Start looking to fall…

Retrospective: September05, Cedar River above Chester Morse Start looking to fall…

2005 Fall Forecast Less dependant on initial conditions than Spring forecast. Monthly updates to ESP traces adds little additional knowledge. Updates to initial conditions very important for Winter/Spring. Forecasts improve as lead time decreases What are current forecast indications…

IRI - ENSO forecast Very high probability of neutral conditions continuing for several months. Streamflow forecast system set to uses ENSO neutral years only (42 traces)

CPC Elevated probability of above average temperatures for next 10 months Precipitation  EC for the next five months,  Elevated chance of above average precipitation starting in May and lasting for the Spring months,  Returning to equal changes for the coming Summer. Seems to always have above average temperature!

October05: Cedar River above Chester Morse

October05: Sultan River inflows to Spada Reservoir

October05: Green River into Howard Hansen

Mid-range Forecasts for Utilities in the Puget Sound Web based delivery and distribution of pdf summary

Mid-range Forecasts for Utilities in the Puget Sound Probability of not exceeding given historic flow thresholds MONTH min 25th 50th 75th max 05/ / / / / / Ensemble predicted flows (cfs) at specified percentiles MONTH 1% 5% 10% 20% 30% 40% 50% 60% 70% 80% 90% 95% 99% 05/ / / / / / Graphic and tabular forecasts of streamflows into the water supply reservoirs on the Cedar, S.F. Tolt, Sultan and Green Rivers

Additional Forecast Information and Products Current conditions, summary of most recent month, and year to date at SeaTac and Paine Field Average Temperature at SEATAC for 09 / Average 09 temp at SEATAC Departure from norm This is the 34 warmest (22 coldest) instance of month 09 in the record from 1950 to 2004 Total Precipitation at SEATAC for 09 / inches Average 09 precipitation at SEATAC inches Departure from norm This is the 13 driest (43 wettest) instance of month 09 in the record from 1950 to 2004

Additional Forecast Information and Products Probabilistic climate forecasts at weather stations used in hydrologic simulations (16 stations)

Additional Forecast Information and Products Simulated “current conditions” in areas without monitoring information Probabilistic snow state forecasts  At monitored locations (SNOTEL)  And unmonitored (FAUXTEL)

Experimenting with Dynamic Data Layer within Google Earth Free downloadable Earth browser We area producing Puget Sound Water Resources Forecast data overlay Linked to updateable database of forecast information

Mid-Range Streamflow Forecasts for Water Supply Management in the Puget Sound Region Matthew Wiley Richard Palmer October 26, 2005