River stresses in anthropogenic times: Large-scale global patterns and extended environmental timelines

Abstract

Global perspectives on the complexities of environmental change impacts associated with past and present human activity are needed for the food and water security challenges of the twenty-first century. This is especially true for rivers, for which the onset and persistence of a range in human activities, altering their function and form, have been temporally and spatially variable. Ancient civilisations, states and empires extended geographically to cover sub-continental areas where their river modifying activities became linked to regional Earth system stresses arising from climate and land use change. We present a new interpretative framework for characterising and classifying human impact on river systems, emphasising that this has taken place over decadal to millennial time periods on a sub-continental scale. This 16-element classification and documentation of different human transformations, including land management, urbanisation, industry and engineering activities, is used to explore anthropogenic channel and floodplain disruptions that have followed each other in different sequences in different places. It is significant that these inadvertent and deliberate human interventions have also taken place in parallel with contrasting climatic fluctuations that have been sub-continental in scale and varied in time. We assess the influence of the dominant modes of regional climate variability (monsoons, El Niño Southern Oscillation, Indian Ocean Dipole, North Atlantic Oscillation, Pacific Decadal Oscillation and Siberian High) on the speed and pattern of river system adjustment to anthropogenic perturbations. Some river civilisations have proved resilient to change given their adaptive management, while others have been overwhelmed by climate-related changes in river morphodynamics. We conclude that integrated socioeconomic, climatic and hydromorphological histories provide usefully instructive antecedents for sensibly managing, as they evolve, the even more serious coupled environmental stresses likely in the future.

Human influence on the morphological adjustment of river channels: The evolution of pertinent concepts in river science

“…The evaluation of specific systems, illustrated for Fountain Hills, Arizona, USA, is one way of holistically assessing how present systems achieve stated objectives and are sustainable. Such evaluations could be very significant in the light of the conclusion by Macklin and Lewin () that for the Anthropocene, it is desirable to disaggregate the global contextual histories and regional susceptibilities of rivers to environmental perturbations. Perturbations in response to future global changes may require the development of new concepts that will require existing ones (Tables and ) to be adapted and further evolved.…”

“…For example, bankfull capacity and channel morphology are not now considered as the product of single channel‐forming flow frequency but rather is determined by the combination of relatively low flows that play an important role in fine sediment transport and bed configuration (e.g., Ma, Huang, Nanson, Li, & Yao, ). For impounded rivers, a hierarchy of impacts was emphasized (Petts, ), and for longer term change, much more information has been obtained by comparing data bases of dated alluvial units with direct or proxy records so that more detailed river responses and the record of late Quaternary environmental changes could be collated (Macklin & Lewin, , , ). Greater understanding of interaction of the two timescales was facilitated by concepts of reaction time and relaxation time (Graf, ), and a further focus for investigations was how change occurred.…”

Changes in floodplain geo-ecology in the Belgian loess belt during the first millennium AD

“…Variation in human activities has greatly impacted the processes and intensities of erosion, sediment transport and storage throughout the Late Holocene, and many lowland rivers around the world have responded to these variations (Notebaert & Verstraeten, 2010;Brown et al, 2018;Macklin & Lewin, 2019). The process-response relationship on a long timescale has been well established: The general concept of fluvial response following human disturbances in NW Europe is that of continuously increasing human impact since Neolithisation which caused a continuous aggradation in the floodplain, although delayed (e.g.…”

Evaluation of extremal hypotheses in an undeveloped alluvial river

“…Initial quantitative work focused on straight irrigation channels to predict cross-sectional dimensions of width, depth, slope, and velocity, which require the least long-term maintenance (Blench, 1957;Inglis, 1947;Jefferson, 1902;Kennedy, 1895;Lacey, 1929;Lindley, 1919). More recently, river management has shifted away from stable planform design to an alluvial corridor perspective that highlights the importance of geomorphic adjustment and rates of change across various spatial scales (Biron et al, 2014;Copeland et al, 2001;Kondolf, 2011;Piégay et al, 2005) to allow for the prediction of evolutionary trajectories that account for climate change and anthropogenic impacts (Brierley and Fryirs, 2005;James, 2017;Macklin and Lewin, 2018). Quantitative methods to account for these trajectories are based on early work in regime theory that later spawned numerous investigations into empirical, theoretical, and optimal approaches for predicting fluvial systems in dynamic equilibrium.…”