Climate and landscape control on seasonal and annual water balance in snow-influenced catchments

Snowmelt-driven streamflow provides water for ecosystems and one billion people. The total and temporal variability of available streamflow depends on how water fluxes are influenced by individual catchments and their climatic setting. Climate factors typically cause different seasonal and annual water balance between large regions but influences on local variations remain less understood. Here we show how both climate and landscape (expressed as soil drainage nonlinearity) control seasonal and annual water balances of 219 snowy catchments across the contiguous United States. These highly diverse catchments are first classified into three groups that are largely climatologically homogenous. This grouping indicates that climate (aridity and climate seasonality) causes distinct hydrological differences between regions. We apply a common framework to these separate group that indicates that climate also shapes what factors further drive within-region differences. Specifically, in humid catchments with winter-dominated precipitation (located in the Pacific Northwest) streamflow seasonality and annual water balances are insensitive to differences in the fraction of precipitation falling as snow (snow fraction). In relatively arid catchments with winter-dominated precipitation (located in the Rocky Mountains) larger snow fractions lead to more annual streamflow with stronger streamflow seasonality and their higher soil drainage nonlinearity enhances these effects. However, in the Northeast and the Great Lakes (where precipitation is less seasonal or summer dominated) higher soil drainage nonlinearity leads to less streamflow. We explain these paradoxical sensitivities by showing how the effect of soil drainage nonlinearity and snow fractions vary regionally depending on the prevailing water and energy balance regimes.