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Daily Scale Dew Point Anomaly Driven Snowpack Ablation in Vermont
Grunes, Anna
Grunes, Anna
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Abstract
Climate change impact on snowpack reduction is often conceptualized as increased average temperature resulting in snow ablation, and a shift in precipitation type favoring rain over snow. However, such descriptions of snowpack decrease underestimate the outsize impacts of short-term, individual weather anomalies on snowpack in the northeastern United States. Such “January thaw” type weather events occur at the daily or sub-daily scale, in contrast to the monthly or seasonal averages commonly used for snowpack impact studies. Here, we quantify how these events are increasing in frequency in Vermont. Such events, often characterized by above-freezing dry bulb temperatures, high dew point temperatures (humidity), rain, and strong southerly winds, are dominant drivers of intra-seasonal snowpack loss. As such, they can act as a key mechanistic link between climate change and snowpack loss. By comparing the changes in meteorological variables that occur within these anomalous periods at high temporal resolution, we quantified the impact of mid-winter thaws by analyzing the changes in high-quantile temperature, humidity, wind, and the co-occurrence of these variables. We find a robust trend showing a doubling of the frequency of daily scale dew point anomalies since 1960. Dew point anomalies are known to dominate snowpack ablation. We also report an increasing frequency of snow ablation co-occurring with short-term dew point anomalies, underscoring the importance of this process in northeastern snowpack dynamics. Compared to frequency, we find slightly less robust trends in the magnitude of thaws that co-occur with snowpack ablation. Finally, we find that southerly winds are consistently associated with the impactful high temperature and humidity, as expected, suggesting that climate change impact evaluations on northeastern snowpack should consider changes to larger-scale atmospheric dynamics that bring about such short-term weather anomalies.
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2022-01-01