PNNL

Abstract

Low snow levels over the past few decades and predictions of a low-to-no snow future have spurred research into snow droughts, which pose a threat to water security and management. Systematic data-model comparisons of snow drought have been lacking, hindering our understanding of the drivers of snow drought in the past. To address this gap, we analyzed snow drought events using standardized snow water equivalent index derived from monthly results of four numerical experiments using the E3SM Land Model (ELM) during the period of 1980-2014. Additionally, we compared snow drought duration calculated from models with those from the ERA5-Land data during selected El Niño-Southern Oscillation (ENSO) years. The numerical experiments were conducted with ELM driven by atmospheric forcings from two prescribed atmospheric forcings, and with the coupled land-atmosphere configuration of E3SM with and without plant hydraulics (PHS) feedback. Analysis reveals that 20-30% of snow droughts occur due to factors other than above-normal temperature and low snowfall, such as low soil moisture, warm soil temperature, and low relative humidity etc., especially in high latitudes (50o north). Furthermore, our study highlights the exacerbating effect of ENSO events on snow drought conditions in various regions, despite some discrepancies between model and ERA5-Land results. We also found the limitations of the coupled land-atmosphere models in our current configuration in capturing the spatial patterns of snow droughts. Our study underscores the challenge of predicting and mitigating snow drought and the need for a comprehensive understanding of the factors contributing to snow drought.