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Hydrography is the branch of physical geography that studies the waters of the planet, thus covering rivers, seas, oceans, lakes, glaciers, groundwater and the atmosphere.

The hydrographs It is the professionals who study the hydrography of the planet, analyze and catalog the navigable waters of the world, elaborating charts and maps that show in detail the formation of the channels, the depth of the waters and the location of the channels, sand banks, sea currents. , etc. Hydrographers are also responsible for studying the influence of winds on the rhythm of waters and tides.

The hydrosphere is the liquid layer of the earth. It is made up of over 97% of water, concentrated mainly in oceans and seas, but also includes water from rivers, lakes and groundwater. In total, the water contained in the planet covers a volume of approximately 1,400,000,000 km³. Already the continental waters represent just over 2% of the water on the planet, with a volume of around 38,000,000 km³.

Liquid water passes into the atmosphere as a vapor in a process called evapotraspiration. The low temperatures of the atmosphere cause this vapor to condense into its liquid state and thus precipitate on the surface.

Scheme evapotraspiration

During the year, about 119 thousand cubic km over the continents precipitate, and only 47 thousand cubic km do not return to the atmosphere, remaining in the oceans, circulating as fresh water.

This difference between precipitation and evaporation is called water surplus and turns into rivers, lakes or groundwater. The water cycle has three main trajectories: precipitation, evapotranspiration and vapor transport.

Water cycle path

The freshwater courses, where civilizations were born, developed and died, are vital to almost all human actions. In Brazil, most of the electricity that reaches homes and industries comes from hydroelectric dams.

Aerial photograph of Itaipu - binational hydroelectric power plant located on the Paraná River, on the border between Brazil and Paraguay

Rivers are also erosive agents of relief, shaping it at their leisure. These net streams, which result from water concentration in valleys, can originate from several sources: underground sources (which form with rainwater), overflow of lakes or even from melting snow and glaciers.