Dryland Rivers and Streams

We outline key features of dryland rivers and illustrate how they differ from temperate and tropical rivers, identify gaps in the understanding of dryland rivers, and illustrate how the functioning of these systems is expected to vary under human impacts. The main concepts we cover are (1) defining dryland rivers and distinguishing them from temperate and tropical rivers, (2) exploring the geomorphological, hydrological, and biological processes of dryland rivers, (3) illustrating how dryland rivers fit into the context of riparian forests and how the aquatic and terrestrial components of these systems interact, and (4) detailing how the functioning of dryland rivers is expected to change in the context of anthropogenic drivers, including climate change. We demonstrate key features of dryland rivers, including their high hydrological and geomorphological variation, how the biotic components of these systems are adapted to this variability, and how anthropogenic changes are likely to impact the functioning and aquatic-terrestrial linkages characteristic of these ecosystems. We identify knowledge gaps where research on dryland rivers is needed, particularly in arctic regions and areas experiencing intense human pressures driven by urbanization, deforestation, and agricultural development. We further highlight how common features of dryland rivers (e.g., high degree of seasonal variability, habitat fragmentation caused by disconnected flows) make them ideal systems for studying emerging ideas derived from metacommunity theory. Despite their clear ecological importance, recent political efforts to restrict what falls under the purview of the Clean Water Act by removing dryland rivers from these protections demonstrate ongoing threats to their health and persistence, especially in densely populated regions that rely on these systems for water provisioning and flood control. Bringing awareness to these systems and the key ecosystem services and functions they perform is critical for their conservation and protection.