Arid-Zone Rivers as Indicators of Climate Change

Arid-zone rivers exist under marginal fluvial conditions where a change in climate can lead to significant changes in flow regime, sediment transport and associated channel style. This chapter provides a brief review of the main characteristics of arid-zone fluvial environments (precipitation and runoff, sediment load, channel morphology, alluvial terraces and slackwater deposits) which may record changes in arid-zone climate. It also identifies a number of problems associated with using arid-zone rivers as indicators of climate change, namely: that the influence of climate on fluvial processes and landforms is poorly understood and has led to incorrect interpretations; that individual large floods and intrinsic threshold conditions can produce landforms and sedimentary sequences which are not in themselves evidence of climate change, for they are not in equilibrium with the prevailing climate; that there may be a strong element of equifinality in the nature of some channel responses; and that individual features, such as river terraces, can be formed at different stages of climate change in different environments. Attention is focused on using river floodplain and terrace stratigraphy as evidence of palaeoflow regimes and hence, by inference, climate change. As there is no general theory or extensive body of empirical research to assess how rivers respond to variations in climate, a case-study approach is adopted. Climate change is interpreted from alluvial sequences in four separate regional and temporal settings: historical changes on the Colorado Plateau of North America; Late Pleistocene and Holocene changes in the Alice Springs region of central Australia; changes over several glacial cycles of the Late to Mid Pleistocene in the Channel Country, an accretionary alluvial basin in western Queensland, Australia; and finally, the Nile River is examined briefly to provide an example of the climatic inferences that can be drawn from a well-known desert river sourced largely outside the arid-zone. These studies demonstrate that rivers in the arid-zone can provide a detailed picture of Quaternary climate change that correlates with and enhances records of regional and global climate change obtained from other sources, such as lakes, ocean and ice cores, sea-level data, and loess deposits.