Effects of watershed topography, soils, land use, and climate on baseflow hydrology in humid regions: A review

Baseflow is the portion of streamflow that is sustained between precipitation events, fed to stream channels by delayed (usually subsurface) pathways. Understanding baseflow processes is critical to issues of water quality, supply, and habitat. This review synthesizes the body of global literature investigating relationships between baseflow and watershed characteristics of geomorphology, soil, and land use, as well as the potential effects of climate change, with an emphasis on humid, tropical and temperate (non-snowpack-dominated) regions. Such factors are key controls on baseflow through their influence on infiltration, rates of water removal from the catchment, and subsurface storage properties. The literature shows that there is much that remains to be resolved in gaining a solid understanding of the influence of watershed characteristics on baseflow. While it is clear that watershed geomorphology influences baseflow, there is no consensus on which geomorphic parameters are most closely linked to subsurface storage and baseflow. Many studies associate higher watershed forest cover with lower baseflows, attributed to high evapotranspiration rates of forests, while other studies indicate increased baseflow with higher watershed forest cover due to higher infiltration and recharge of subsurface storage. The demonstrated effects of agriculture and urbanization are also inconsistent, due to varied additions of imported water and extremely variable background conditions. This review underscores the need for more research that addresses multiple aspects of the watershed system in explaining baseflows, and for methodological consistency to allow for more fruitful comparisons across case studies. These needs are of immediate demand, given scientific and management emphasis on environmental flows required for maintenance of key ecosystem services.