1. 2005 Water Resources Outlook for Idaho and the Western U.S.
JISAO Center for Science in the Earth System
Climate Impacts Group
and Department of Civil and Environmental Engineering
University of Washington
October, 2004
Alan F. Hamlet
Andy Wood
Dennis P. Lettenmaier

2. Background

3. Background: Forecast System Schematic
NCDC met. station obs. up to 2-4 months from current
local scale (1/8 degree) weather inputs
soil moisture
snowpack
Hydrologic model spin up
SNOTEL Update
streamflow, soil moisture,
snow water equivalent, runoff
25th Day, Month 0
1-2 years back
LDAS/other real-time met. forcings for spin-up gap
Hydrologic forecast simulation
Month
INITIAL STATE
SNOTEL
/ MODIS*
Update
ensemble forecasts
ESP traces (40)
CPC-based outlook (13)
NCEP GSM ensemble (20)
NSIPP-1 ensemble (9)
* experimental, not yet in real-time product

4. Seasonal Climate Forecast Data Sources
ESP
ENSO/PDO
ENSO
CPC Official Outlooks
Seasonal Forecast Model (SFM)
CAS
OCN
SMLR
CCA CA
NSIPP-1 dynamical model
VIC Hydrology Model
NOAA
NASA UW

5. Background: Hydrology Model

6. Background: Estimating Initial Conditions SNOTEL assimilation
Assimilation Method
weight station OBS’ influence over VIC cell based on distance and elevation difference
number of stations influencing a given cell depends on specified influence distances
spatial weighting function
elevation
weighting
function
SNOTEL/ASP
VIC cell
distances “fit”: OBS weighting increased throughout season
OBS anomalies applied to VIC long term means, combined with VIC-simulated SWE
adjustment specific to each VIC snow band
important point(s):
the approach attempts to make use of forecast skill from 2 sources:
better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models;
the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling).
Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

7. snow cover (MODIS) assimilation (Snake R. trial)
Framework: Estimating Initial Conditions
snow cover (MODIS) assimilation (Snake R. trial)
Snowcover BEFORE update
Snowcover AFTER update
MODIS update for April 1, 2004 Forecast
snow
added
removed

8. Background: Streamflow Forecast Locations
California
Columbia R. basin
in development:
Colorado R.,
Upper Rio Grande
Snake R. basin

9. Linkage to Reservoir Models
Streamflow
Forecast
Bias Correction
Storage
Ensemble
Reservoir Model
Observed Reservoir
Contents
Demand Scenarios

10. ColSim
Storage Forecast

11. Recap of Water Year 2004

12. Initial Conditions for Winter 2003-04
Soil Moisture and Snow Water Equivalent (SWE)

13. Initial Conditions for Winter 2003-04
Soil Moisture and Snow Water Equivalent (SWE)

14. Initial Conditions for Winter 2003-04
Soil Moisture and Snow Water Equivalent (SWE)

15. Initial Conditions for Winter 2003-04
Soil Moisture and Snow Water Equivalent (SWE)

16. Initial Conditions for Winter 2003-04
Soil Moisture and Snow Water Equivalent (SWE)

17. Winter 2003-04: PNW streamflow
By Fall, slightly low flows were anticipated
By winter, moderate deficits were forecasted

18. Winter : seasonal volume forecasts Comparison with RFC forecast for Columbia River at the Dalles, OR
UW forecasts made on 25th of each month
RFC forecasts made
several times monthly:
1st, mid-month, late
(UW’s
ESP unconditional and
CPC forecasts shown) UW
RFC

19. Last winter: volume forecasts for a sample of PNW locations

20. Last winter: volume forecasts for a sample of PNW locations

21. Last winter: volume forecasts for a sample of PNW locations

22. Last winter: volume forecasts for a sample of PNW locations

23. Last winter: volume forecasts for a sample of PNW locations

24. Last winter: volume forecasts for a sample of PNW locations

25. Last winter: volume forecasts for a sample of PNW locations

26. Evaluation of Last Year’s ColSim
Storage Forecast
Obs.Sys Storage
Sept 15, 2004

27. System Storage Forecast from SnakeSim:
Jackson Lake
Palisades
Island Park
Ririe
American Falls
Lake Walcott
11 ENSO neutral years (reshuffled 3 times)
Random historic demand scenarios
Full Pool
Active Reservoir Storage (kaf)
Obs. Storage
Sept 30, 2004
Green = ensemble mean

28. Outlook for Water Year 2005

29. Winter Climate Forecasts Dominate Hydrologic State Variables Dominate
April 1 SWE (mm)
Winter Climate
Forecasts Dominate
Hydrologic State
Variables Dominate
June
December
March
Range =16.7%
of ensemble
summer mean

30. Initial Soil Moisture Conditions

34. Natural Flows at Milner 1928-1989

35. Simulated Natural Flow at Milner (Oct ESP Nino3.4 between +0.2 and +1.2)

36. Upper Snake Storage Climatology
Historic water years
Storage
Sept 30, 2004

37. System Storage Forecast from SnakeSim:
Jackson Lake
Palisades
Island Park
Ririe
American Falls
Lake Walcott
Nino3.4 anomaly between 0.2 and 1.2 C
Demand aligned with water cond.
October 1 Spin Up
Active Reservoir Storage (kaf)

38. Impacts of the West-Wide Drought on the Pacific Northwest

39. 1930s Drought Soil Moisture
Soil moisture-defined drought
Percent severity
SAD curve to left. To right, raw percent severity (below 80% is white) on top panel, drought classifications on bottom panel. Consistently severe for areas up to ~ 5 km^2 up to 36 month duration. At this point areas are encompassing cells that only experience drought for a few of the 36+ months.
Figure courtesy of Elizabeth Clark and Kostas Andreadis, UW

40. Current Drought Soil Moisture
Soil moisture-defined drought
Percent severity
Severity for longer duration drops quickly with area, while remaining durations are fairly consistent in severity up to ~ 3.5 million km^2.
Figure courtesy of Elizabeth Clark and Kostas Andreadis, UW

41. Concluding Remarks
Soil moistures in Oct, 2004 are wetter overall in comparison with Oct, 2003.
Drought risks appear to be about the same as last year based on likely mid-winter Nino3.4 anomalies, and the highest likelihood is for flows clustered around normal conditions (very high and very low flows unlikely). However, one very high and one very low flow year have both occurred for this range of Nino3.4 anomalies, so both extremes cannot be ruled out.
The wild card is the West-wide drought. If the large scale climate anomaly that has impacted precipitation over the west continues to impinge on southern Idaho, analogue years based on Nino3.4 anomalies may not be very representative. Will the drought continue, and will it impact Idaho if it does?