Water balance

A system can be one of several hydrological or water domains, such as a column of soil, a drainage basin, an irrigation area or a city.

According to the US Geological Survey:[4] An understanding of water budgets and underlying hydrologic processes provides a foundation for effective water-resource and environmental planning and management.

Comparison of water budgets from different areas allows the effects of factors such as geology, soils, vegetation, and land use on the hydrologic cycle to be quantified.A general water balance equation is:[5] where This equation uses the principles of conservation of mass in a closed system, whereby any water entering a system (via precipitation), must be transferred into either evaporation, transpiration, surface runoff (eventually reaching the channel and leaving in the form of river discharge), or stored in the ground.

[7] To estimate the drainage requirement, the use of a hydrogeological water balance and a groundwater model (e.g. SahysMod[8]) may be instrumental.

[9] “Making water available for its many uses and users requires tools and institutions to transform it from a natural resource to one providing services”.

Under various drivers, such as, climate change, population increase, and bad management, water storage of many WRS is decreasing, say per decade.

This means that the volume of water in a WRS decreased after a decade, i.e., inflow was less than outflow during that time interval.

[11] In general, a WUS is a water construct of a user, such as a city, an industry, an irrigation zone, or a region, and not a geographic area.

Considering that the annual change in storage of an urban area is negligible, water balance equation becomes