1. Quantitative vs. qualitative analysis of snowpack, snowmelt & runoff
Interannual variability in Eastern Sierra precipitation, snow accumulation, runoff amount/timing is high relative to projected changes in the period.
Although snow index sites (snow pillows/courses) that form the basis for (statistical) seasonal water supply outlooks do also give an indication of past trends, they do not provide a basis for quantitative estimation of snowpack amount & distribution.
Accurately determining the current amount & distribution of snow water equivalent requires spatial data, i.e. from satellite remote sensing.
Accurately projecting future trends at the basin scale must build on accurate estimation of snow distribution & melt.

2. Point physically based method
Provides a point of comparison for traditional water-supply outlooks, but pushes statistical relations outside range of calibration
Outlooks perform well near the mean, but poorly at the extremes, i.e. upper & lower tercile of snow accumulation
See western Sierra example; analysis not yet done for eastern Sierra basins
Bias in April 1 forecasts (under-forecast) for July-April unimpaired runoff for 15 Sierra Nevada basins was about 150% of average accumulation, i.e. a wet year.
Unpublished data, CADWR

3. Distributed physically based approach
An analysis of coarse-scale data provides basically the same result as does an analysis of the coarse-scale outputs from various climate-model simulations.
Possible influence of a +3oC increase in average daily temperature
snow vs. rain
snow season length
rain flood storms
From Bales, R. C. , N. P. Molotch, T. H. Painter, M. D. Dettinger, R. Rice, and J. Dozier, Mountain hydrology of the western United States, Water Resources Research,W08432, doi: /2005WR004387,2006
Note that these data are at the scale of the VIC model & are adapted from VIC model inputs, after Mauer et al., 2002.
historical fraction of annual precipitation that fell in the
range -3 to 0oC
number of days per year with mean temperature -3 to 0oC
fraction of 25 largest storms with temperatures in the -3 to 0oC range

4. Distributed physically based approach
SCA time series provides only basis for basin-wide SWE estimation, which is an essential input for distributed, physically based modeling to develop streamflow scenarios.
Without accurate mass balance, modeling must be based on calibration, which adds uncertainty since the scenarios will likely lie outside the range of calibration.
Note also issue with snow courses failing to provide distributed, representative measures of snowpack. Only 6 of the sites on the E side in these basins have snow pillows (reporting to CDEC).
Historical SCA time series can be used to build the distributed data needed for credible runoff scenarios

5. Sierra Nevada snow covered area (SCA), 2004
Data developed from MODIS satellite
Spatial resolution: 500 m
Temporal resolution: daily
SCA aggregated into 4 bins to aid in viewing
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 67 – March 7

6. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 71 – March 11

7. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 72 – March 12

8. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 73 – March 13

9. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 76 – March 16

10. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 78 – March 18

11. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 79 – March 19

12. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 80 – March 20

13. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 87 – March 27

14. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 96 – April 5

15. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 133 – May 12

16. Sierra Nevada snow covered area (SCA), 2004
Owens Valley
1-25
26-50
51-75
76-100
% SCA
DoY 176 – June 25

17. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Closeup of 5 headwater basins.
Note that resolution of spatial data is 500 m
Green circles are snow-course locations
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 67 – March 7

18. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 71 – March 11

19. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 72 – March 12

20. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 73 – March 13

21. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 76 – March 16

22. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 78 – March 18

23. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 79 – March 19

24. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 80 – March 20

25. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 87 – March 27

26. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 96 – April 5

27. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Note that considerable snow remains at elevations above the snow courses, highlighting the critical need to spatial estimation of current snow amounts as a basis for projections based on future climate scenarios
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 133 – May 12

28. Sierra Nevada snow covered area (SCA), 2004
Rock
Pine
Birch
Bishop
Big Pine
1-25
26-50
51-75
76-100
% SCA
DoY 176 – June 25