Human and natural systems are tightly linked in coastal areas, where hydrologic processes are intensifying. Studying these processes is important for understanding vulnerability to water resources, improving management capabilities for flood forecasting and risk assessment, water supply planning, water quality, and ecosystem protection and restoration. The coastal critical zone (CZ) is a “hotspot" of biogeochemical activity, where large quantities of nutrients and Blue Carbon are cycled and stored. In the coastal CZ nutrients and anthropogenic pollutants that are deleterious to water-quality and ecosystems are trapped and attenuated, reducing fluxes to the coastal ocean. Thus, changes in the coastal CZ and transformation of coastal landscapes have important implications not only for ecosystems, human communities, and the global economy, but also for global elemental fluxes. We welcome submissions on exchange of surface and groundwater in coastal watersheds; hydrologic controls on sediment supply and salinity; and compound extremes (i.e. hurricanes and atmospheric rivers).