|Title||Winter snow level rise in the northern Sierra Nevada from 2008 to 2017|
|Publication Type||Journal Article|
|Year of Publication||2017|
|Authors||Hatchett B.J, Daudert B., Garner C.B, Oakley N.S, Putnam A.E, White AB|
|Type of Article||Article|
|Keywords||america; atmospheric rivers; california; climate projections; mountain; Nevada; precipitation; rain; Sierra nevada; snow; snow level; snowpack; streamflow; variability; Water resources; western united-states|
The partitioning of precipitation into frozen and liquid components influences snow-derived water resources and flood hazards in mountain environments. We used a 915-MHz Doppler radar wind profiler upstream of the northern Sierra Nevada to estimate the hourly elevation where snow melts to rain, or the snow level, during winter (December-February) precipitation events spanning water years (WY) 2008-2017. During this ten-year period, a Mann-Kendall test indicated a significant (p < 0.001) positive trend in snow level with a Thiel-Sen slope of 72 m year(-1). We estimated total precipitation falling as snow (snow fraction) between WY1951 and 2017 using nine daily mid-elevation (1200-2000 m) climate stations and two hourly stations spanning WY2008-2017. The climate-station-based snow fraction estimates agreed well with snow-level radar values (R-2 = 0.95, p < 0.01), indicating that snow fractions represent a reasonable method to estimate changes in frozen precipitation. Snow fraction significantly (p < 0.001) declined during WY2008-2017 at a rate of 0.035 (3.5%) year(-1). Single-point correlations between detrended snow fraction and sea-surface temperatures (SST) suggested that positive SST anomalies along the California coast favor liquid phase precipitation during winter. Reanalysis-derived integrated moisture transported upstream of the northern Sierra Nevada was negatively correlated with snow fraction (R-2 = 0.90, p < 0.01), with atmospheric rivers representing the likely circulation mechanism producing low-snow-fraction storms.