Hydrologie

Hydrologie, or hydrology, is the science that studies the distribution and movement of Earth's water. It analyzes the occurrence of water in the atmosphere, on the surface, in soils and rocks, and how water interacts with living organisms and human activities. The discipline draws on physics, chemistry, geology, and geography to describe patterns and processes.

The hydrologic cycle encompasses precipitation, evaporation and transpiration, infiltration and percolation, runoff, and the storage and movement of water in soils, rivers, lakes, and aquifers. Hydrology distinguishes surface-water hydrology, which focuses on rivers, lakes, wetlands, and floods, from groundwater hydrology, which studies aquifers and subsurface flow. Hydrometeorology links weather and water, emphasizing how atmospheric processes influence water supply and hazards.

Data and methods rely on field observations (rain gauges, stream gauges, groundwater wells), remote sensing, and hydrological modeling. A central concept is the water budget: precipitation minus evapotranspiration minus runoff plus changes in storage equals zero. More detailed budgets may include groundwater storage changes. Hydrological models range from simple empirical rainfall–runoff models to complex distributed physically based models, often integrated with geographic information systems and data assimilation.

Applications cover water resources management, flood forecasting and risk assessment, drought monitoring, irrigation planning, hydropower, ecological flow assessment, urban drainage, and climate-change impact analysis. Subfields include hydrogeology, surface-water hydrology, ecohydrology, and hydroinformatics, each addressing different aspects of water movement, quality, and its ties to ecosystems. The field has historical roots in systematic rainfall and discharge measurements and the development of groundwater hydraulics, notably Darcy’s law, with formal hydrology maturing in the 19th and 20th centuries.