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  • Author or Editor: Daniel J. McEvoy x
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Benjamin J. Hatchett
and
Daniel J. McEvoy

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.

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Daniel J. McEvoy
,
Justin L. Huntington
,
John T. Abatzoglou
, and
Laura M. Edwards

Abstract

Nevada and eastern California are home to some of the driest and warmest climates, most mountainous regions, and fastest growing metropolitan areas of the United States. Throughout Nevada and eastern California, snow-dominated watersheds provide most of the water supply for both human and environmental demands. Increasing demands on finite water supplies have resulted in the need to better monitor drought and its associated hydrologic and agricultural impacts. Two multiscalar drought indices, the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), are evaluated over Nevada and eastern California regions of the Great Basin using standardized streamflow, lake, and reservoir water surface stages to quantify wet and dry periods. Results show that both metrics are significantly correlated to surface water availability, with SPEI showing slightly higher correlations over SPI, suggesting that the inclusion of a simple term for atmospheric demand in SPEI is useful for characterizing hydrologic drought in arid regions. These results also highlight the utility of multiscalar drought indices as a proxy for summer groundwater discharge and baseflow periods.

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