Understanding End‐of‐Century Snowpack Changes Over California's Sierra Nevada

Abstract

This study uses dynamical and statistical methods to understand end‐of‐century mean changes to Sierra Nevada snowpack. Dynamical results reveal that middle‐elevation watersheds experience considerably more rain than snow during winter, leading to substantial snowpack declines by spring. Despite some high‐elevation watersheds receiving slightly more snow in January and February, the warming signal still dominates across the wet season and leads to notable declines by springtime. A statistical model is created to mimic dynamical results for 1 April snowpack, allowing for an efficient downscaling of all available general circulation models from the Coupled Model Intercomparison Project phase 5. For all general circulation models and emission scenarios, dramatic 1 April snowpack loss occurs at elevations below 2,500 m, despite increased precipitation in many general circulation models. Only 36% (±12%) of historical 1 April total snow water equivalent volume remains at the century's end under a “business‐as‐usual” emission scenario, with 70% (±12%) remaining under a realistic “mitigation” scenario.

Association of genetic and climatic variability in giant sequoia, Sequoiadendron giganteum, reveals signatures of local adaptation along moisture‐related gradients

“…A trend toward increased aridity along midelevation Sierra Nevada forests could undermine the long‐term persistence of giant sequoia. With end‐of‐century predictions for this region that include decreasing snowfall and earlier snowmelt, forests of the Sierra Nevada mountains will likely experience an accentuation of the summer drought that is typical of Mediterranean climates (Fyfe et al., 2017; Stewart, Cayan, & Dettinger, 2004; Sun et al., 2018). Considering the evidence presented here, we highlight the potential that increased water stress may create maladaptation of giant sequoia populations to their environment.…”

“…The slow release of water from snowmelt in the spring is an important source of moisture for seedling growth and establishment. Sierra snowpack has declined in recent years (Fyfe et al., 2017) and high‐resolution regional climate models suggest that spring snow water equivalent will decline by 73% by the end of the century, with midelevations (1,500–2,500 m) experiencing the greatest declines (Sun, Berg, Hall, Schwartz, & Walton, 2018).…”

Evapotranspiration feedbacks shift annual precipitation-runoff relationships during multi-year droughts in a Mediterranean mixed rain-snow climate

“…Our study considered two spatial scales (Figure 1): the Feather at Oroville Dam and three of its headwater sub-basins: Almanor (∼1100 km 2 , 1400-2900 m ASL, rain-shadowed), East Branch (∼2600 km 2 , 725-2550 m ASL, rain-shadowed), and Middle Fork (∼2700 km 2 , 480-2660 m ASL, partially rain-shadowed). Hydrologic studies on the Feather River at Oroville are abundant (see for example Tang and Lettenmaier, 2010;Rosenberg et al, 2011;Huang et al, 2012;Anghileri et al, 2016, and references therein), whereas headwater sub-basins have rarely been studied as stand-alone catchments (see examples in Freeman, 2011;Wayand et al, 2015;Sun et al, 2019).…”

Climate elasticity of evapotranspiration shifts the water balance of Mediterranean climates during multi-year droughts

“…For example, higher elevations of the Sierra Nevada have P > ET even in dry years, whereas lower elevations can switch from having P > ET in wet years to P < ET in dry years. These differences can be driven by local regolith lithology (see, e.g., Tague et al, 2008;Tague and Grant, 2009) as well as climate and the interaction of the two over long time periods (Klos et al, 2018).…”