the science that studies natural waters and the phenomena and processes occurring in them. As a geophysical science, hydrology is in close contact with the sciences of geographic, geologic, and biological cycles.
The subject matter of hydrology is bodies of water—that is, oceans, seas, rivers, lakes, reservoirs, swamps, and accumulations of moisture in the form of snow cover, glaciers, and soil and subterranean waters. The main problems of present-day hydrology are to investigate the hydrologic cycle and the influence on it of human activity, as well as the control of the regimen of bodies of water and the stream-flow regimen of territories; to perform space-time analyses of hydrologic elements (water level, discharge, temperature, and so on) for individual territories and the earth as a whole; and to discover patterns in the variations of these elements. The principal practical application of hydrology is in the evaluation of the present state of water resources, in forecasting their future state, and in laying the basis for their rational utilization.
Based on the specific characteristics of bodies of water and of the methods of their study, hydrology is divided into oceanography (hydrology of the sea), land hydrology (hydrology proper; more precisely, hydrology of the surface water of land), and hydrogeology (hydrology of subterranean water).
Hydrology initially developed as a branch of physical geography, hydraulic engineering, geology, and navigation and took shape as a system of scientific knowledge only at the beginning of the 20th century. A definition of hydrology as a science was provided by V. G. Glushkov in 1915. A large role in the formation of hydrology was played by the establishment in 1919 of the State Hydrologic Institute. Present-day hydrology makes wide use of methods employed in geography, physics, and other sciences, and the role of mathematical methodology is steadily increasing.
A. A. SOKOLOV and A. I. CHEBOTAREV