This subject area deals with the science of the circulation of water in the earth-atmosphere system i.e. the water cycle. The water cycle is the circulation of water evaporated from the sea and land surfaces, its transport through the atmosphere to the land and its return to the sea via surface, subsurface and atmospheric routes. Although called a cycle, the process is much more complex than a mere cycle. All kinds of short-cut and parallel processes take place. For example, a drop of water evaporated from the sea may precipitate back into the sea without completing the entire cycle. The water cycle refers to the general circulation, which results from the fact that there is on average above the earth's land surface more precipitation than evaporation. Water precipitated over land passes through a number of storage media, which can be regarded as subsystems of the water cycle.
Surface detention and interception storage are considered as separate systems. Interception storage refers to the precipitation intercepted by vegetation before it evaporates. Detention storage is water temporarily stored in pools or depressions. This water may evaporate or infiltrate into the soil to replenish the soil moisture reservoir or percolate to the groundwater. The flow of soil moisture in downward direction is called percolation and in upward direction capillary rise. The annual amount of percolation is usually larger than capillary rise, resulting in a recharge of groundwater reservoir. Groundwater flow ultimately discharges from the groundwater storage into the channel system.
Most often the study of the water cycle, on a catchment or basin scale, can be represented quantitatively through a water balance. Trying to understand the inter-linkages between various components of water balance is the subject of hydrologic modeling. In general, a model is a mathematical or physical description that represents a physical, biological or social system. It simplifies the complexity of the real world to a certain degree of accuracy and a fundamental objective of hydrological modeling is to provide reliable information for water resources management such as:
- to predict extreme events, such as floods, low flows and rainstorms;
- to interpolate and extrapolate a hydrological time series;
- to provide insights into physical, chemical or biological processes involved in the hydrological system;
- to support decision making in relation to design, planning, operation and management of water related infrastructural measures and man-induced changes in the hydrological regime including climate change.
Hydrologists apply scientific knowledge and mathematical principles to solve water-related problems in society: problems of quantity, quality and availability
- Hydrologist/Flood specialist
- Flood risk assesor
- Water Resource Modelling