Drivers of Variation in Winter and Spring Groundwater Recharge: Impacts of Midwinter Melt Events and Subsequent Freezeback

Abstract

AbstractIn areas with seasonal snowfall, the spring snowmelt often accounts for a large percentage of annual groundwater recharge. As climates warm, midwinter snowmelts are becoming more common. Although midwinter melt events can cause discrete recharge events, they can also increase soil water content and leave the ground exposed to subsequent cold periods. Without the insulating effects of snow, frozen ground can develop, which can prevent infiltration during subsequent melt events, reducing recharge, and increasing overland flow. We investigated relationships between winter precipitation, the soil thermal regime, and recharge to determine the factors that contribute to variation in winter‐spring recharge. We found that statistically significant predictors of variation in winter‐spring recharge, controlling for precipitation, were amount and cover of snow, evapotranspiration/sublimation, air temperature, and number of freezeback events occurring between two melt events. We observed that midwinter snowmelt followed by freezeback and subsequent melt events correlated with lower than expected recharge. We quantify the occurrence of this sequence of events (snowmelt followed by freezeback and another melt) and demonstrate its effect in reducing recharge in a multiyear, multilocation statistical analysis. This finding indicates that frozen ground plays a role the partitioning of precipitation between recharge and runoff, but the effect is sensitive to the magnitude and temporal sequence of precipitation events and temperature fluctuations. Understanding the complex relationships between snow, midwinter melt and freezeback events, frozen ground, and recharge is critical for predicting how climate change will affect groundwater resources in the future.