There appears to be some contention about whether the snow pack in California is increasing, decreasing or wiggle waggling. Now Eli is a RTFR kind of bunny and when someone provides a reference tends to follow the tracks, and sometimes when there is no clue he follows the Rabett tracks using the dread google. Sometimes Eli learn something, as indeed was this case when upon googling Sierra snowpack a paper by Kapnick and Hall by popped up
To assess inter-annual variations in California snowpack evolution, a metric was developed for quantifying systematic changes in snow accumulation and melt timing. In particular, we focused on the timing of peak snow mass. We created a measure of the timing of peak snow mass relying on SWE [snow water equivalent- er] observations taken around the first of the month from February to May.which, among other things, made the points that SWE on April 1 is an indicator of the water supply that will be available for the rest of the year
We used these monthly snapshots rather than daily SWE data because the daily data are only robustly available from 1980 to the present, too short a time series to calculate long-term trends in maximum SWE timing.
The peak snow mass timing is defined for any given year as the temporal centroid date, also known as the center of mass, of SWE values (SWE centroid date, or SCD) from approximately 4 February 1 to May 1 for stations with complete data over this four-month time period.
A study of the California Sierra snowpack has been conducted using snow station observations and reanalysis surface temperature data. Monthly snow water equivalent measurements were combined from two data sets to provide sufficient data from 1930 to 2008. The monthly snapshots are used to calculate peak snow mass timing for each snow season. Since 1930, there has been a trend toward earlier snow mass peak timing by 0.6 days per decade. The trend towards earlier timing also occurs at most individual stations. The majority of stations have experienced simultaneous reductions in April 1 snow water equivalent. Reductions in April 1 snow water equivalent may therefore be due to earlier snowmelt rather than reductions in total snowfall. Analysis of individual years and stations reveals that warm early spring temperatures are associated with earlier snow mass peak timing for all spatial and temporal scales included in the data set. The influence is particularly pronounced for low accumulation years indicating the importance of albedo feedback for the melting of shallow snow. Regional mean averaged March and April temperatures have increased at a rate of 0.1°C or 0.2°F per decade since 1948, and the robustness of the average early spring temperature influence on peak timing suggests the trend towards earlier peak timing is attributable to the temperature trend. Given scenarios of warming in California, we can expect to see acceleration in the peak timing trend; this will reduce the warm season storage capacity of the California snowpack.emphasis added. What water folk like Brian care about is the amount of water available to carry CA through the summer and fall, until it starts to rain and snow again. The Sierra functions as a huge reservoir which stores water over the winter and releases it well into the late spring. As the water makes its way through the hydrological system in the spring and sumer when rainfall in CA is scarce, it provides water for the cities and farms. The later the SCD and the higher the SWE then, the greater the water supply. If the trend in SCD continues, at a minimum CA will have to invest heavily (wes are poor, taxes are high and government is evil) in expanding its reservoir system.