Analysis of geomorphic systems’ response to natural and human drivers in northern Spain: Implications for global geomorphic change

An analysis of changes experienced during the last century by certain indicators of the intensity of geomorphic processes in northern Spain is presented, in order to test a previously formulated hypothesis. The hypothesis, already tested in the Rio de la Plata Basin, is that there is a global geomorphic change which implies an acceleration of geomorphic processes in general, and that such acceleration is mainly due to the transformation of land surface by human activities, not to climate factors. Sedimentation rates obtained in eight estuaries in northern Spain, through Pb-210 and Cs-137 dating of sediment cores, show a general increase since the beginning of last century, and particularly after the 1950s. Similar increases in landslide frequency have been formerly observed in some areas of the same region. Trends of change in sedimentation rates have been compared with those of potential natural (rainfall) and human (indicators of the intensity of human activities that can contribute to land-surface transformation) drivers. There seems to be no relationship between rainfall and sedimentation rate trends but the magnitude and trends of several indicators of human activity are similar to those of the latter. Data on landslide frequency obtained in a small study area also show a possible relationship with land-use change and infrastructure development, but not with rainfall. The results described are coherent with the hypothesis and suggest that the process described could have a global character. If this is so, the worldwide observed increase in flood and landslide disasters might be a characteristic of the Anthropocene and due to human-induced geomorphic change, rather than climate change (also human-induced), as often assumed. ► 20th century sedimentation rates in N Spain show in general increasing trends. ► Increasing rates do not seem to be related to rainfall trends. ► Indicators of human activity provide a better match with sedimentation rate trends. ► Results are coherent with an acceleration of processes (global geomorphic change). ► Increasing geomorphic hazards appear to be a consequence of that change.