Exploring the Origins of Snow Drought in the Northern Sierra Nevada, California

Abstract

The concept of snow drought is gaining widespread interest as the climate of snow-dominated mountain watersheds continues to change. Warm snow drought is defined as above- or near-average accumulated precipitation coinciding with below-average snow water equivalent at a point in time. Dry snow drought is defined as below-average accumulated precipitation and snow water equivalent at a point in time. This study contends that such point-in-time definitions might miss important components of how snow droughts originate, persist, and terminate. Using these simple definitions and a variety of observations at monthly, daily, and hourly time scales, the authors explore the hydrometeorological origins of potential snow droughts in the northern Sierra Nevada from water years 1951 to 2017. This study finds that snow droughts can result from extreme early season precipitation, frequent rain-on-snow events, and low precipitation years. Late-season snow droughts can follow persistent warm and dry periods with effects that depend upon elevation. Many snow droughts were characterized by lower snow fractions and midwinter peak runoff events. These findings can guide improved evaluations of historical and potential future snow droughts, particularly with regards to how impacts on water resources and mountain ecosystems may vary depending on how snow droughts originate and evolve in time.

Snow Drought Risk and Susceptibility in the Western United States and Southwestern Canada

“…Defining snow drought types by climatic causes is a relatively new concept (e.g., Harpold et al, ). While several recent studies have increased our understanding of snow drought (e.g., Cooper et al, ; Hatchett & McEvoy, ; Sproles et al, ), a regional assessment of snow drought risk has never before been completed. In this study, the dry versus warm snow drought definition proposed by Harpold et al () was expanded to include snow droughts that are caused by the co‐occurrence of warm and dry conditions.…”

“…Defining snow drought types by climatic causes is a relatively new concept (e.g., . While several recent studies have increased our understanding of snow drought (e.g., Cooper et al, 2016;Hatchett Note. Volume (vol.)…”

“…Water & McEvoy, 2018;Sproles et al, 2017), a regional assessment of snow drought risk has never before been completed. In this study, the dry versus warm snow drought definition proposed by was expanded to include snow droughts that are caused by the co-occurrence of warm and dry conditions.…”

“…Warm snow droughts reduce the annual flood peak due to increased rain versus snow proportion and a lengthening of the melt interval before the peak flow (Rood et al, ) and also increase flood risk due to rain on snow events (Allamano et al, ; Harpold et al, ; Rood et al, ). Hatchett and McEvoy () showed that in Sierra Nevada watersheds, warm snow droughts correspond to lower snow fractions and often include midwinter flood events. Considering no change in the seasonal timing and magnitude of precipitation, warm snow droughts and the associated lower snow fractions lead to decreased annual runoff (Alexander et al, ; Berghuijs et al, ; Dierauer et al, ) and a shift in water supply away from summer and toward winter (Leith & Whitfield, ; see also Adam et al, ; Alexander et al, ; Déry et al, ; Pederson et al, ; Whitfield & Cannon, , among others), negatively impacting water quantity, water quality, hydropower operations, winter snow sports, and summer recreation (Alexander et al, ; Sproles et al, ).…”

Snow Level Characteristics and Impacts of a Spring Typhoon-Originating Atmospheric River in the Sierra Nevada, USA

“…Heavy October precipitation events create positive water year precipitation anomalies, which can facilitate the onset of warm snow drought conditions if rain occurs rather than snow. Warm snow droughts are characterized by near or above normal precipitation but below normal snowpack [48] and can imply that water is not being stored in the snowpack and must be managed through legally-constrained reservoir operations [14]. Other early water year warm snow droughts related to typhoons include the Columbus Day Storm in October 1962, which had origins as Typhoon Freda, and the water year 2017 warm snow drought initiated by Typhoons Songda and Haima [48].…”