Streamflow Generation across the Diverse Tropics: Heterogeneity, Evidence Gaps, and Hydrological Implications

Abstract

Tropical streamflow research has been shaped disproportionately by work in humid-forest catchments and a small number of disturbed or experimental sites, despite the much wider diversity of streamflow-generating environments across the solar tropics. Drylands, tectonically active rift zones, volcanic landscapes, karst terrain, wetlands, grasslands, internally drained basins, and other diverse tropical environments are comparatively underrepresented in process-based hydrological research. This synthesis examines how climate, landforms, and subsurface structure jointly shape streamflow generation across these and other settings. Two organizing principles recur across contrasting environments: subsurface storage architecture and threshold-controlled connectivity. Fault-controlled aquifers, volcanic and karst substrates, and internally drained basins exert strong but contrasting controls on streamflow generation, storage, and persistence, and can heighten sensitivity to longer-term climatic variation and land-use change. Site-level mechanistic understanding is strongest in systems with sustained, process-based observations, such as Andean páramos, selected montane cloud-forest catchments, glacier-fed systems, volcanic landscapes, and a small number of intensively studied seasonally dry catchments. Persistent uncertainty in subsurface–surface linkages and threshold dynamics across many regions constrains both process understanding and management. Closing these gaps requires sustained, process-resolving observations across underrepresented tropical landscapes, particularly those where livelihoods depend on streamflow regimes most sensitive to climatic and anthropogenic change.