Transcription of The Hydrological Cycle
1 UNESCO EOLSSSAMPLE CHAPTERSHYDROLOGICAL Cycle Vol. I The Hydrological Cycle - Encyclopedia of Life Support Systems (EOLSS) THE Hydrological Cycle Director, State Hydrological Institute, St. Petersburg, Russia Keywords: Hydrosphere, Hydrological Cycle , precipitation, evaporation, river runoff, surface and subsurface water, inflow, water exchange, water balance, water storage, water withdrawal, water consumption, anthropogenic climate change. Contents 1. Introduction: Definitions of Hydrosphere and Hydrological Cycle 2.
2 Composition of the Hydrosphere Distribution of Water Water in Oceans and Seas Subsurface Water Ice, Glaciers, Permanent Snow Cover Subsurface Ice in Permafrost Zone Water in Lakes and Reservoirs Water in River Channels Water in Swamps Soil Moisture Water in the atmosphere Biological Water 3. Schematic Diagram of the Hydrological Cycle 4. Water Exchange in Nature Water Exchange between Ocean and atmosphere : Precipitation and Evaporation from Water Surface Water Exchange between Land and atmosphere ; Precipitation and Evaporation from Land Water Exchange between Land and Ocean; River Runoff Surface and Subsurface Water Interaction 5.
3 On Man s Activity Effects on the Hydrological Cycle Transformation of Vegetation Cover and Earth's Surface Forest and Forestry Effects Land Plowing, Agricultural Practices, Use of Meadows as Pastures Urbanization Reservoirs and Hydromelioration Practices Freshwater Use Man's Impact on Climate by Changing Atmospheric Characteristics Possible Climate Change due to Evaporation Increase Climate Change Resulted from Changes in the Composition of the atmosphere 6. World Water Balance 7. Conclusions Glossary Bibliography Biographical Sketch UNESCO EOLSSSAMPLE CHAPTERSHYDROLOGICAL Cycle Vol.
4 I The Hydrological Cycle - Encyclopedia of Life Support Systems (EOLSS) Summary The Hydrological Cycle is a process of constant water exchange or water circulation in the hydrosphere, in the system of the atmosphere - Earth s surface soil cover - upper lithosphere (to a depth of 2000 m). Water in the hydrosphere is liquid, solid or gaseous; during the Hydrological Cycle it moves under the effect of heat energy, gravitation and capillary forces, converting from a liquid to its solid state or gas, and back.
5 The Hydrological Cycle is one of the major geophysical processes on the planet providing relative stability of natural conditions and continuous distribution of water between ocean, land and atmosphere . Quantitative characteristics of water storage in different parts of the hydrosphere are given in this chapter, water accumulated in the oceans and seas, in aquifers, in ice and permanent snow cover, in lakes and reservoirs, in river channels, in swamps, in soils, in the atmosphere , as well as in living organisms.
6 The general system of the global Hydrological Cycle is considered; it is shown that the contribution of particular type of water to the hydrosphere depends not only on its volume but also on its rate of migration or annual discharge and renewal during the water Cycle . In this sense, water in river channels is advantageous if compared with the other types of water in the hydrosphere: it is renewed quickly during the water Cycle (over 17 days on average), which explains the great importance of river runoff as the basic source of fresh water for different human needs.
7 Water exchange processes are discussed in details in the systems: ocean atmosphere , land atmosphere , ocean land, surface and subsurface water. The results of this exchange are analyzed as mean annual distribution of precipitation, evaporation, river runoff and surface/subsurface runoff on the planet. Much emphasis is focused on the problem of human impact on the Hydrological Cycle and on analysis of the contemporary world water balance as a quantitative characteristic of global Hydrological Cycle components averaged for a long-term period.
8 The effect of changes in the top cover of the Earth, construction and operation of reservoirs, freshwater use for human needs, anthropogenic effects on characteristics of the atmosphere due to higher evaporation because of freshwater use for human needs, and intensive burning of carbonic fuel (oil, gas, coal), are all described. Analysis of the global water balance components has been made for a long-term period (about 50 years) for each continent, ocean and for the whole planet.
9 Finally, brief conclusions are made and objectives are formulated for future research, mainly related to a more accurate estimation of particular types of water storage in the hydrosphere, studies of their exchange, more detailed and reliable assessments of the components of the Hydrological Cycle and world water balance essential under the conditions of observed and expected great changes in the global climate. Quantitative characteristics of the hydrosphere and the global Hydrological Cycle given in this chapter are mainly based on research results obtained by Russian scientists, who UNESCO EOLSSSAMPLE CHAPTERSHYDROLOGICAL Cycle Vol.
10 I The Hydrological Cycle - Encyclopedia of Life Support Systems (EOLSS) traditionally generalize and analyze the data of the world hydrometeorological network and study the dynamics of global water resources and water balance. 1. Introduction: Definitions of Hydrosphere and Hydrological Cycle There is much water on our planet in a free state, forming oceans, seas, lakes, rivers, ice cover, soil moisture and subsurface water; water is available in the atmosphere and biosphere, and it is found in minerals in the Earth s crust, bound chemically and physically.
