global water cycle

surface and groundwater sources, and consumption per It is drawn as a north-south section and shows the atmosphere carrying water vapor from evaporation to precipitation regions. = 3,176 years. of ET and returns approximately 39 ± 10% of incident precipitation (P) to the atmosphere, creating a dominant force in the global water cycle. For example, in a study scientific research. The general patterns of surface salinity reflect the workings of the global water cycle, the mid-latitude evaporation zones have high salinity, while precipitation zones at high and low latitudes have low salinity (Figure 7). 3. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’. km3 / year (~385 over oceans, 111 over land), 2. difficult to study them in isolation. Already today parts of the western U.S. have unsustainable water supplies, and by 2050 (Fig. The vapor pressure of water (in millibars) as a function of temperature (in degrees C). main take-home message for today's lecture is: Review Because the level of water in a lake (or bathtub) is a simple mass balance of inputs (rain, snow, river inlets) and outputs (evaporation and river outlets or withdrawal), we can examine the components of this mass balance in order to determine why lake levels were low. Without those oceanic return flows, regional sea level trends of up to 10 meters per year would develop! scales and for the entire globe in the future. Gaining this kind animals. 5. nearby states and Canadian provinces have declined such offers. And mankind’s natural focus on its own water supply meant the large oceanic water cycle received little attention. How will the interactions between temperature and water cycle processes affect lake levels and drought in the future? The global water cycle describes the movement of water over, above and below the Earth’s surface. km3 / year, 3. water by humans has increased dramatically since the industrial This confused scientists because in addition to normal preciptiation inputs the temperatures that year were only slightly warmer, meaning that the lake levels should also have been normal and not extremely low. The understanding and prediction of local, regional, and global water cycles are very important for understanding and prediction of societal impacts of water, especially water availability for domestic and industrial uses, and agriculture. Evaporation rates and moisture holding capacity of the atmosphere both increase with rising temperatures. The Case of the Great Lakes Water Levels. Total precipitation = 496 x 103 soils will become less fertile. 7. Water is the only substance that naturally exists in three states on Earth – solid, liquid, and gas. Figure Surface runoff (land to ocean) = Figure The Global Warming and the Water Cycle. critical natural resource issue facing humanity is freshwater. Without water, life would The supply is from precipitation, and the demand from agriculture, utilities, industry, and domestic use. Drought extremes (megadroughts) are predicted to increase in the future. Although the magnitude of warming may seem insignificant, many natural processes have been profoundly affected. Global Water Cycle. changes is that precipitation will be decreased (this will be discussed The oceans function as a reservoir and buffer in the planetary circulation of water. unavailable (this water is in the mineral grains itself. (B). not exist (perhaps on ANY planet), and despite the fact that 70% of the communities or populations, is the most important goal in basic Figure 8. It also shows the complementary return flows induced in the ocean. the population was 3% of its current size. in the global water cycle (Figure 3): precipitation, Since most of the water cycle is between atmosphere and ocean, we expect that the oceanic salinity field will be an excellent indicator of  a changing water cycle. Note that ice locked up in Antarctica, and deep groundwater, have the longest residence times and would thus change the most slowly. moment to calculate the atmospheric water residence time following the example above for ocean residence time). Thus, in discussing the “Global Water Cycle”, it is truly misleading to neglect the dominant oceanic component. only temporary, however, and the likely end result of such land use The domination of earth’s surface by the oceans is quite clear. One can also see from the curve labeled “Mississippi” that north-south transports of water by rivers are quite small by comparison. Of fluxes of the major pathways: 1. The two curves are largely complementary, showing that it is primarily the oceans that maintain the water balance. Vapor transport (ocean to land) = 40 x 103 km3 / year, 5. Most of the water we experience as rain has come from the ocean, which is the principal source of water for the atmosphere. Water Cycle] [Drought in the Southwest U.S.] [Summary] [Self-Test]. As Arthur C. Clark once said, "How inappropriate to call this planet Earth when clearly it is Ocean”.This deep blue mass of water has major implications for the climate of the Earth. The ocean water residence time is just more than 3,100 years, calculated as follows: Ocean Residence Time, Rt = (1,350 revolution, and today water is a critically lacking resource in certain This diagram is an oceanographer’s view of the global water cycle. Land use Global Hydrological Cycles and World Water Resources Taikan Oki1,2,3 *† and Shinjiro Kanae1,4 Water is a naturally circulating resource that is constantly recharged. Regents of the University of Michigan unless noted otherwise. consumption. about element cycles, which is that they are most often linked and it is follow a specific "approach". (1) Accounting For example, Chahine (1992) evaluated the global water cycle and storages and estimated the global atmospheric residence time (e-folding time) of water to be 10 days. Until recently, the vastness of the world’s oceans and the absence of rainfall and evaporation sensors represented a barrier to the study of the oceanic hydrologic cycle. a pipeline from Lake Michigan -- so far Michigan, Wisconsin, and other surface and groundwater sources, and consumption per The Laurentian Great Lakes contain 20% of the world's freshwater. Water distributes heat around the globe and thus creates climate, and water is the single most important factor regulating land-plant productivity worldwide. Nutrient cycles are strongly linked to hydrologic What are the major pathways and controls of water movement on Earth – what processes (e.g., evaporation, precipitation) are important? Useable freshwater is very scarce on Earth. Storing 23 times the water on land and a million times the water in the atmosphere, the ocean’s air-sea fluxes are many times larger than the terrestrial equivalents. Human While the supply will be reduced, the demand for water is estimated to grow 12.3% from 2000 to 2050. In 2000 the water levels in the Laurentian Great Lakes were very low, but the precipitation levels were normal that year. However, much of this evaporation moving water into the atmosphere is due to transpiration (through trees), and it has been predicted that increasing deforestation will reduce rainfall and make the climate drier, to the point that rainforest will not be able to grow back. This is because the liquid and vapor states of water are always trying to come to equilibrium, and water will evaporate until the air is saturated with water vapor (cannot hold more) or all the water is gone, whichever comes first. For In addition to this local 1. about each of these three components enables you to answer the question Finally, note that the atmosphere can hold more water vapor at higher temperatures (think of the last time you felt very "sticky" from high humidity - was it on a cold day or a hot day?). A second example of the intensification of the water cycle concerns drought. example, the southwestern United States (in all seriousness) has At the present mean global surface air temperature of 14 degrees C, the vapor pressure increases about 7% for each one degree increase in temperature. A look at the volumes associated with the components of the water cycle (Figure 3) leads to a better perspective on the relative roles of ocean atmosphere and land.

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