It was along the Indus in Pakistan, the Tigris and Euphrates in Mesopotamia, the Hwang Ho in China, and the Nile in Egypt that the first hydraulic engineers created canals, levees, dams, subsurface water conduits, and wells as early as 5000-6000 years ago.

It is defined as the transfer of liquid water into vapor state to the atmosphere. It involves the conversion of water from liquid to vapor state and then again return to the atmosphere in the form of liquid or solid precipitation that reaches the earth surface.

The rate of evaporation is defined as the amount of water evaporated from a unit surface area per unit of time. It can be expressed as the mass or volume of liquid water evaporated per area in unit of time, usually as the equivalent depth of liquid water evaporated per unit of time from the whole area.

It is defined as the fall of moisture from the atmosphere to the earth surface in any physical form. Usually precipitation is in two forms: Liquid - rainfall Solid Precipitation

In hydrology we apply scientific knowledge and mathematical principles to solve water-related problems in society: problems of quantity, quality and availability. Mathematical models of all Hydrological phenomena are made.