Incised fluvial systems are typically interpreted as recording geologically recent changes in either climate or tectonics. However, few diagnostic tools exist to evaluate whether particular incised landscapes primarily reflect climatic or tectonic perturbation. Here we summarize the results of a simple fluvial sediment transport model that allows us to contrast patterns of fluvial incision driven by changes in hydrology and sediment flux (“climate”) with those driven by changes in rock uplift patterns relative to sea level (“tectonics”). Our modeling suggests that there may be diagnostic differences between the spatial and temporal patterns of incision caused by these different processes. In particular, incision driven by climate change is most commonly accompanied by downstream migrating waves of incision and decreases in channel gradient, while under most circumstances incision driven by tectonics will be accompanied by upstream migrating incision and increases in channel gradient. We apply our modeling to a case study of the North American High Plains, where regionally elevated surfaces east of the Rockies have been incised up to 500 m by the fluvial systems draining the core of the range. Although this incision has been interpreted as reflecting a tectonic rejuvenation of the High Plains, our analysis suggests that climate change is at least as plausible an explanation to explain the incision of this landscape. Diagnostic differences between the climate and tectonic end-member scenarios might be obtained via detailed study of the spatial and temporal patterns of terrace abandonment, providing a potentially fruitful target for field investigation.