Abstract: Warming in the Arctic is expected to lead to greater variability in rain precipitation. It is
not yet known how this variability will affect the coupled hydrology and thermal dynamics of
continuous permafrost areas. We used an observation-informed thermal-hydrology model of a
hillslope-riparian zone draining to a headwater stream to quantify how rain variability,
independent of the long-term mean, affects the hydrologic behavior of a supra-permafrost
aquifer along a typical hillslope in the North Slope of Alaska. We used climate records (1981 –
2020) to generate synthetic rainfall, systematically altering rain variability while keeping other
hydroclimate conditions unchanged. We conducted 108 ensemble numerical simulation
experiments covering the summer rain season while keeping total cumulative rain and other
climate forcings at their 40-year day-of-year means, so that any differences in modeled
response were due to rain variability alone. Results show that increased rain variability
amplifies transient groundwater fluxes during storm events, reduces inter-storm drainage and
increases outflow flashiness by more than 100% across the variability range. Increased rain
variability alters water table position, water saturated thickness, and the timing and magnitude
of hillslope outflow to the stream. Integrated hydrologic responses show that as rain variability
increases, there is an increase in cumulative downslope outflow, reduced evapotranspiration,
and reduced surface-to-subsurface fluxes. Because the export and transformation of soil carbon
from aquifers depend on soil moisture and groundwater flow, changes in rain variability will
affect carbon cycling in Arctic landscapes.