River networks dampen long‐term hydrological signals of climate change

River networks may dampen local hydrologic signals of climate change through the aggregation of upstream climate portfolio assets. Here we examine this hypothesis using flow and climate trend estimates (1970–2007) at 55 hydrometric gauge stations and across their contributing watersheds' within the Fraser River basin in British Columbia, Canada. Using a null hypothesis framework, we compared our observed attenuation of river flow trends as a function of increasing area and climate trend diversity, with null‐simulated estimates to gauge the likelihood and strength of our observations. We found the Fraser River reduced variability in downstream long‐term discharge by >91%, with >3.1 times the attenuation than would be expected under null simulation. Although the strength of dampening varied seasonally, our findings indicate that large free‐flowing rivers offer a powerful and largely unappreciated process of climate change mitigation. River networks that integrate a diverse climate portfolio can dampen local extremes and offer climate change relief to riverine biota.