Controls on Flow Permanence in Temporary Rivers: A Framework of Hydrogeomorphic Processes Across Space and Time.

Abstract:

Temporary rivers, those rivers that periodically cease to flow, constitute over half of the total discharge of the global river network and are expected to increase in extent as a consequence of climatic shifts and water resource development. Despite their ubiquity, projected increased frequency, and ecological significance, the spatial and temporal controls on flow permanence remain poorly understood. Hydrogeomorphic research to date on temporary rivers has primarily focused on network expansion and contraction patterns with comparatively little consideration of mechanistic controls on temporary streamflow dynamics. The present work integrates hydrologic, geomorphic, and land cover processes across spatiotemporal scales that control streamflow dynamics in temporary rivers that are meaningful to ecological research in these systems. We first present a conceptual diagram that describes spatiotemporal expansion and contraction cycles of temporary rivers. Spatiotemporal dynamics of network expansion and contraction are complex; however, commonalities in wetting and drying patterns and degrees of connectivity exist at network (>10³m), reach (10^1-3m), and local (<10¹m) spatial scales. Next, we propose a spatiotemporal framework to evaluate hydrologic, geomorphic, and land cover controls on temporary streamflow based on a synthesis of the current state of knowledge. For example, we identify specific precipitation patterns and watershed characteristics that influence flow permanence across spatial and temporal scales that range from the watershed to sub-meter and millennial to hours. Finally, we discuss research priorities for temporary rivers that can elucidate confounding interactions and directionality of hydrology, geomorphology, and land cover on flow permanence. Two methods priorities for future field research are: use of tracers and isotopes for identifying age, sources, and pathways of water within a riverscape and monitoring networks for assessing spatiotemporal patterns of surface and subsurface flow within temporary river networks. Currently, we are forced to infer from studies of perennial rivers and a few well studied temporary rivers. Further temporary river specific research is required to test and validate our assertions.