Increased summer air temperatures in interior Alaska have caused drought stress and growth suppression in several boreal tree species. The response of Alnus tenuifolia (thinleaf alder) to a warming climate could substantially impact interior Alaskan floodplains due the role alder plays as the dominant N-fixer. We studied the effects of inter-annual variation in monthly meteorological and hydrological variables on annual alder radial growth (directly related to N-fixation input), the landscape variability in alder climate sensitivity, and the long-term trends in climate and hydrology. Alder ring-width was positively correlated with the Palmer Drought Severity Index and river discharge in June, and with river discharge in August, suggesting vulnerability to moisture limitation. The sensitivity of alder radial growth to variation in river level was inversely related to site terrace height, while sensitivities to variation in air temperature and precipitation were positively related to terrace height. This variation in climate sensitivity underscores the importance of meteorological versus hydrologic controls on soil moisture availability and alder radial growth across the landscape. Long-term meteorological and hydrologic trends in this region suggest that drought will become more common and severe, resulting in alder growth suppression and reductions in alder-mediated ecosystem N inputs.