<p>The relation of regional precipitation and streamflow sensitivities to warming is complicated by runoff often being the small residual in the balance between precipitation and evapotranspiration. In addition, the inhomogeneous nature of land-hydrological properties and hydrological interventions by humans, like irrigation and dams, have made streamflow sensitivities challenging to constrain with both climate models and observations. Here, we elucidate the hydrological processes driving the regionally varying mean and extreme streamflow sensitivities to warming across the contiguous United States in a counter-factual warming scenario using GFDL’s moderately high-resolution global climate model. We show that over the West Coast and eastern US, atmospheric rivers are the dominant driver of high-flows in the present climate and of more frequent high-flows in a warmer climate. Over the mountainous western US, streamflows dwindle despite increases in precipitation and antecedent soil moisture, as loss of snow fuels evapotranspiration at double the rate of precipitation changes.</p>