Two main branches of hydrology are:
- Surface water hydrology: This branch of hydrology deals with the study of the movement, distribution, and quality of surface water, including rivers, lakes, and wetlands. This includes the study of precipitation, evaporation, snow and ice, and the water cycle in general. Hydrologists in this branch study the physical, chemical, and biological processes that govern the movement and distribution of surface water and its interactions with the environment.
- Groundwater hydrology: This branch of hydrology deals with the study of the movement, distribution, and quality of groundwater. This includes the study of aquifers, wells, and springs, as well as the interaction of groundwater with surface water and the environment. Hydrologists in this branch study the physical, chemical, and biological processes that govern the movement and distribution of groundwater, and how groundwater interacts with the subsurface environment.
Both of these branches are interrelated as surface water and groundwater are part of the same water cycle and are connected through infiltration and discharge. Hydrologist also use their understanding of surface water and groundwater to study and mitigate the effects of natural hazards such as floods and droughts, and to manage and protect water resources for drinking, irrigation, and other uses.