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2. The Hydrologic Sciences
Pages 32-61

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From page 32...
... The global distributions of rainfall, snowfall, evaporation, and accumulated surface and subsurface water affect the local extent and global distribution of biomass and biological productivity. Changes in land cover and biological productivity can, in turn, affect hydrologic processes on both local and global scales.
From page 33...
... Theories for the uniqueness of water on the earth fall into two classes, genetic and evolutionary. The genetic theory holds that chemical equilibrium of accreting gas and dust in the solar nebula led to the formation of solid constituents richer in hydrated minerals at greater distance from the proto-sun.
From page 34...
... ~ ~ ~ ~ ~ ~: ~ ~ ~ :~ ~: ~ ~ ~ ~ ~ ~ ~: ~ ~ ~ ~ ~ ~ ~: ~ ~: :water~rat: 1~er~:~:an:~ surmce~runon~: ls ~ t~oom~nant~agen~t~:carv~ng~t~r:~ ~:val~leys.:: ~ :~ :: ~ ~ :~ ~: ~ ~ ~ ~ ~ :~ :: ::: ::: ~:: ::: :~: ~ ::~ ::~ C~-~ :: :~: ~: r~ : ::: : : ~: a ~ T : :~ ~ ~ ~ ~: ~ ~ ~ ~: :~ ~ ~ :~ ~ :~ ~ ~ ~ ~::~:~: :~ ~;~ ~;~ ~ ~ ::~: : ~ :o~m~parl son~ ot~ ::p~rocesses on ~t~ne~:two ~p la:nets :~s hou Id~ :~reveal ~m~h ~: a:boUt~::~ ~:~ ~:the~cha:racter ~ of:~ru~h~off Droduct~ion~ark:f~its~:~intera:ction~:~wi+~Ma~rv Sr~:lr( - r'`a~ : ~4 1 ~ ~ca ~ ~_ · ~ : ~ ~ : ~ ~ ~: : ~ :: ~: ~ : ~ :: ~ ~ :: :~ :~:: -53°C, leading to the presence of seasonal polar caps of frozen carbon dioxide and to speculation that there may be extensive subsurface frozen water. It appears that the earth also once had a carbon dioxide atmosphere that was sharply reduced by some unique process (most probably biological)
From page 35...
... This process is called the hydrologic cycle. It is the framework of hydrologic science (Figure 2.2)
From page 36...
... These are dissolved in ground water and carried to the oceans, where
From page 37...
... The central role of water in the evolution and operation of the earth system provides a rationale for seeing hydrologic science as a geoscience whose stature equals that of the ocean, atmospheric, and solid earth sciences. EARLY SCIENTIFIC INSIGHTS Concern for water as both a necessity of life and a possible hazard has been with humans throughout their existence.
From page 38...
... Water scientists and engineers focused their attention on drainage basins commonly having a characteristic horizontal scale of 10 to 100 km. Because the early foundations of hydrologic science were built on experience with the middle latitudes, some inadvertent and long-lived biases were established.
From page 39...
... in the United States founded an elegant theory that describes ground water flow. Until late in the nineteenth century hydrologic research in the United States remained the province of enterprising professors, inventors, prospectors, and wealthy amateurs.
From page 40...
... The fate of this proposal illustrates the status of hydrologic science within the U.S. scientific community during the first half of the twentieth century.
From page 41...
... ME HYDRO[OGlC SCONCES 47 In using the hydrologic cycle to define the processes encompassed by hydrologic science, Horton recognized the diversity of scales by stating: may natural exposed surface may be considered as a ~H area on which me hydrologic cycle operates. This includes, far example, an isolated tree, even a single leaf or Wig of a growing plant, the roof of a building, me drayage bash of a dver-system or any of its ~~utaries, an undrained glacial depression, a swamp, a glacier, a polar ice-cap, a group of sand dunes, a desert plays, a lake, an ocean, or me Earn as a whole.
From page 42...
... 42 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES Throughout Horton's definitive work it is apparent that 1. the central focus was still on the conservation of water mass at the scale of the river basin, where evaporation was characterized as a "water loss"; 2.
From page 43...
... E Meinzer (geologist in charge, Division of Ground Water, USGS)
From page 44...
... 44 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES i: ~ ~~ ~ ~ ~~ ~: ~ ~~ ~ ~ ~~ ~~ ~~ ~~ ~~ :: ~ ~~ ~ ~~ ~~1~g~.7~1~9~8~2') ~ ~~ ~~h~i~s~:~l:o.~n~ ~~a~n~d~d~i~t~i~n~9u~i~sh~.r~e~r.~:~i:~W~a~l~ter~ ~~:~l:~n~hp~;~n~r1~v~r~;~l~il~ ~~ ~~ ~~ ~ ~ to ~~ Erect ~~ As ~~sŁ~l~e~n~t~t~i~c~ ~~ e~n~d~eavo rs~ Toot ~~e~:~pu~ '~ C -cow ~~.~ ~~ :~ : : angbein was born in Newark, New Jersey, on Octo r; 17,: ;9:07;.
From page 45...
... Consideration of the temperate latitude megalopolis and tropical latitude deforestation made it clear that the lateral scales of human alteration of the land surface were becoming commensurate with those of atmospheric moisture exchange. The feedback effects of land surface state on the influential atmospheric processes had acquired a practical importance, and it was realized that the necessary science base was missing.
From page 46...
... Without doubt, however, volcanic activity continuously vents water vapor to the atmosphere (V') and liquid water to the oceans (VO)
From page 47...
... from ice E,e = Evapotranspiration from land = Intrusion of seawater into continental aquifers L = Loss of water to space PO = Precipitation on oceans 47 = PI = Precipitation on ice P,e = Precipitation on land R = Runoff from continents S VO Vat W = Subduction of water containing crust Volcanic venting to oceans Volcanic venting to atmosphere - Wastage of ice sheets to ocean FIGURE 2.4 The hydrologic cycle as a global geophysical process. Enclosed areas represent storage reservoirs for the earth's water, and the arrows designate the transfer fluxes between them.
From page 48...
... Water vapor is the most important of the greenhouse gases, acting to regulate the earth's surface temperature by absorbing and returning to the earth much of the thermal radiation emitted there. Oceanic precipitation (PO)
From page 49...
... For example, the direct ground water flow to the sea is missing from ATMOSPHERE ~ ~ - nws-~ - ~ ~ — Precipitation ~ ~ 107 / ~ Evaporation & TransDiration if\ Evaporation ~~ / ICE & SNOW ~ / BIOMASS :~ 43,400 of_ ~ '. 2 : : : ~ : ~ ~ _ :_ Ernie ~ ~ ~ ~ ~ ~ ~ _0 _ ~ ,$ ~ ~ ~ r — _ —~~ ~ ~ ~ i:: ::~:~::~i~: :~:i~:~:~:~:l SURFACE WATER r ~ :~:: ~ :: :: :~:::: : i:: :: : :: :: ::::: : :: :: :: :: .
From page 50...
... With typical residence times of days to months, it provides the driving potential for moisture fluxes in the soil: upward to the roots of plants and as evaporation, and downward in recharging ground water. It serves the same storage and driving functions for dissolved chemical species.
From page 51...
... In other words, given the dynamics at microscale, how can behavior at the macroscale be represented? This scale-transfer problem arises in the hydrologic sciences in attempts to describe the coupled fluxes of heat and moisture across large land surface elements, to couple the microscopic molecular processes of chemical reactions to the macroscopic averages of ground water transport equations, and to establish appropriate parameters for use in describing the behavior of ground water plumes at field scale.
From page 52...
... Particularly needed are new observational techniques to study and monitor the rates of snow accumulation and snow and ice melt over remote areas. Because of the sensitivity of snow and ice reservoirs to climate change, it is important to monitor closely the extent of snow cover, the mass balances of mountain glaciers and ice sheets, and the West Antarctic ice sheet with its fringing ice shelves.
From page 53...
... Such understanding would reveal fundamental scaling relationships of surface water hydrology over a broad range of spatial scales (i.e., 1 to 106 km2) and would have immediate applicability to flash flood forecasting in ungaged watersheds and to parameterization of hydrologic processes in regional and global models.
From page 54...
... As water infiltrates the soil and moves downward, it picks up carbon dioxide from the soil, exchanges solutes with soil and rock particles, and becomes less acidic. The percolating waters convey their solute load through the ground water and into streams.
From page 55...
... Energy production, farming, urbanization, and technology have altered the albedo of the earth, the composition of its soil and water, the chemistry of its air, the amount of its forest, and the structure and diversity of the global ecosystem. These actions of humans now extend to the "ends of the earth" high latitudes, deserts, and mountains, where they affect sensitive environments and where hydrologic data and understanding are ab
From page 56...
... data. HYDROLOGIC SCIENCE AS A DISTINCT GEOSCIENCE In 1931 Horton identified a hydrologic science of limited scope that was motivated by engineering practice to understand the quantity and movement of water at the small catchment scale.
From page 57...
... Hydrologic science can now be seen as a geoscience interactive on. a wide range of space and time scales with the ocean, atmospheric, and solid earth sciences as well as with plant and animal sciences.
From page 58...
... Similar trespassing must occur in '~4~Ns If. Oceans ~ ~~\~ 5G~ s~cea/seRegion FIGURE 2.8 Hydrologic science: a distinct geoscience.
From page 59...
... There is little doubt that coping with these issues in a timely fashion will require a much-improved scientific understanding of the earth system and its component parts. Unified and coherent treatment of hydrologic science is central to this larger effort.
From page 60...
... 1962. Scientific Hydrology.
From page 61...
... 1971. Scientific Framework of the World Water Balance.


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