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 2011-2040 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.

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. 2005 was about 150% of average accumulation, i.e. a wet year. Unpublished data, CADWR

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:10.1029/2005WR004387,2006 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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