Diverging Impacts of Snow Fraction and Soil Drainage on Seasonal and Annual Water Balances Across Snow-Influenced Catchments

Abstract

Snowmelt-driven streamflow provides water for ecosystems and for 2 billion people. While climate shapes distinct water balances across regions, its influence on variations within individual regions remains less constrained. This can result in regionally uncertain climate impacts on local streamflow. Here we show how both climate and soil drainage nonlinearity (estimated by modeled nonlinearity of saturated-zone recharge to root-zone storage) control seasonal and annual water balances of 230 snow-influenced catchments across the contiguous United States. Classification of these catchments into three groups with largely uniform climates indicates that climate (here: aridity and climate seasonality, defined as the seasonal magnitude of the difference between precipitation and potential evapotranspiration) causes distinct regional hydrological differences. Our application of a common water-balance framework to these groups indicates that climate also shapes what factors further drive within-region hydrological differences. In humid catchments with winter-dominated precipitation (located in the Pacific Northwest), streamflow seasonality and annual water balances show little sensitivity to differences in the fraction of precipitation falling as snow (snow fraction). By contrast, in relatively arid catchments with winter-dominated precipitation (i.e., the Mountain West) larger snow fractions increase streamflow and its seasonality significantly, with these effects amplified by greater soil-drainage nonlinearity. In further contrast, in the Northeast and the Great Lakes (where precipitation is less seasonal or summer-dominated) stronger soil drainage nonlinearity reduces annual streamflow. We explain these diverging impacts on streamflow by showing how the effect of soil drainage nonlinearity and snow fractions vary regionally depending on the prevailing water and energy balance regimes.