Dryland Fluvial Environments: Assessing Distinctiveness and Diversity From a Global Perspective

The idea that dryland fluvial environments are somehow distinctive or even unique compared to fluvial environments in wetter and/or cooler climatic settings has arisen in much of the literature, despite the fact that drylands are themselves inherently diverse, covering a wide range of local climatic, tectonic, structural, lithological, and phytogeographical settings. Focusing on rivers in warm drylands, this chapter outlines the main characteristics of dryland rivers, including flow and sediment transport conditions, channel forms and dynamics, channel and floodplain sedimentology, and equilibrium and nonequilibrium behavior. Although dryland rivers are commonly ascribed a set of restricted characteristics that have been derived mainly from studies in short, steep, tectonically active catchments, investigations in larger, lower-gradient, tectonically stable catchments have revealed much greater diversity in river character both within and between drylands, and have demonstrated overlap with river characteristics in other climatic settings. With this global perspective, I argue that many previous statements regarding the distinctiveness of dryland river characteristics either can no longer be sustained as generalizations, or, at the very least, the geographical and geomorphological contexts for those generalizations need to be clarified. One of the key priorities for future research will be to identify and explain the spatial extent and frequency of occurrence of river styles across different drylands. In particular, research into the controls of meandering, straight, and anabranching rivers characteristic of some moderate-to low-energy Southern Hemisphere drylands has not only contributed to greater appreciation of the global diversity of dryland rivers but is also leading to a better understanding of rivers in general. Technological and methodological developments (especially in geochronology) are enhancing understanding of dryland river process, form, and change, and this will continue to facilitate interdisciplinary work in diverse scientific and applied contexts.