Emerging dominance of summer rainfall in driving High Arctic terrestrial-aquatic connectivity

Abstract Climate warming-related hydrological transformations are changing material mobilization, composition, and transport pathways along the terrestrial-aquatic continuum. Here, we integrate decade-long hydrometeorological and biogeochemical data from the High Arctic to show that annual fluvial energy is shifting from a skewed (snowmelt-dominated) to a multi-modal (snowmelt- and rainfall-dominated) distribution. This shift enhanced terrestrial-aquatic connectivity for dissolved and particulate material fluxes, but to overcome the watersheds’ buffering capacity for particulate material rainfall events had to increase by an order of magnitude. Permafrost disturbances (< 3 % of the watersheds’ areal extent) reduced watershed-scale DOC export enough to offset concurrent increased DOC export in undisturbed watersheds but play a weaker role in altering C export than the increased magnitude and frequency of late summer rainfall events. However, the disturbances have primed the landscape for accelerated geomorphic change when future rainfall magnitudes and consequent pluvial responses exceed the current buffering capacity of the terrestrial-aquatic continuum.