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3. Some Critical and Emerging Areas
Pages 62-213

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From page 62...
... The evolution of sedimentary basins and the genesis of ore deposits are fundamentally influenced by ground water flows operating on time scales of 102 to 106 years and spatial scales 62
From page 63...
... One challenge we still face is to improve our understanding of the interaction between the hydrologic cycle and the general circulation of the ocean-atmosphere system. There is a
From page 64...
... The interaction between land surface processes and regional weather is another exciting frontier in hydrologic science. For instance, under what conditions will the spatial distribution of evaporation generate regional circulations that could influence mesoscale rainfall and regional climate?
From page 65...
... It is precisely in the interplay between the different scales that the hydrologic cycle offers unique scientific challenges in the search for general principles. In plant dynamics it is known that the abundance of species and their spatial distribution are related to environmental conditions called ecological optima.
From page 66...
... Acid rain is a clear example of the importance of understanding and predicting the effects of the chemical composition of precipitation. The use of rainfall composition data as tracers of the hvdrolo~ic cycle offers singular opportunities to better understand J ~ J V 1 1 the relationship between the chemistry of rainfall and the chemistry of soils, ground water, and surface waters.
From page 67...
... In fact, they look as if they were a stochastic process, and thus the phenomenon is called deterministic chaos. Is this phenomenon detectable in hydrologic processes?
From page 68...
... Hot springs develop when meteoric water originating from rainfall or snowmelt circulates to depths of several kilometers, adsorbs heat from the surrounding rock matrix, and then is able to move relatively quickly to the ground surface along fault zones. Figure 3.1 shows how heat flow from deeper levels of the earth's crust can be captured by the ground water flow system and diverted to a major fault zone.
From page 69...
... The vadose zone is a storage component of the hydrologic cycle, a reservoir of water, air, and reactive inorganic and organic solid matter. It influences the runoff cycle and ground water recharge by affecting both the flow patterns and the quality of surface and percolating subsurface waters.
From page 70...
... Although rates of ground water flow are much lower than those in the upper few hundreds of meters of the earth's surface, and time scales may approach 106 years or longer, from a geologic viewpoint ground water circulation within the upper crust is no less important than the near-surface component of the hydrologic cycle. Permeability is the parameter that quantifies the ability of a fluid to flow through the interconnected pore spaces of a rock or soil.
From page 71...
... Recently, attempts have been made to quantify the role of ground water flow in regional metamorphism, where, for example, a rock such as limestone is transformed to marble. The concepts and tools of hydrologic analysis are being adopted to solve a number of fundamental geoscience problems, and opportunities abound for collaborative research.
From page 72...
... 72 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES EM. KI N AH U~B {HE RT~: ~ it's ~~: ~~ ~ ~ :~ ~ ~ :: : ~ A:: ~~ ~~ ~~ ~~ ~~ ~ ~ ~ aft: ~~ :: ~ Buff 9Q~3~1~9~891~ ~~:~: :: :: ~~ ~: I: ~ : i: ~ ;~: : A:: : ~ : I: ~ Hi: ~~ i: ~ : ~: ~~:~:~I~Ngeoph~ys~i~cs"~:s~ ~~m~uch~:br~er ~that~:~t~na::rr~a~ppl~c~ion~:~:~: Amp; ~~ ~ ~ ~ ~~ ~ ~ ~~ ~ ~~ ~ ~ ~ ~ ~ ~ ~ .
From page 73...
... When rocks slide past each other along a fault, friction generates heat. Thermal pressurization within a fault zone during faulting can cause fluid pressures to rise to near-lithostatic values, leading to strain weakening as the earthquake progresses.
From page 74...
... Fluid pressures approaching lithostatic values can develop during the evolution of a sedimentary basin because of the combined effects of compaction of the sediments, heating of confined fluids, and dehydration of clay minerals. These overpressures modify the flow patterns from those that would be predicted solely on the basis of ground water recharge from regions of higher elevation within the basin.
From page 75...
... Most studies are based on the concept of homogeneous rock properties, but there is little reason to expect that spatial variability will be any less important at depth than it is for near-surface environments. Similarly, there is a paucity of detailed data to test hypotheses and model assumptions rigorously.
From page 77...
... As a result, it is probable that largescale patterns and rates of fluid flow and mass transfer at greater depths within the crust are controlled by fractures and shear zones. It has yet to be established that conventional modeling approaches, based on assigning medium properties such as permeability to representative volumes of the rock mass, provide the correct framework to quantify mesoscale ground water flow and solute transport in deeper crustal rocks.
From page 78...
... There are two approaches to the description of ground water flow in geologic media containing fractures: (1) the continuum approach, which treats the fractured medium as if it were equivalent to a porous medium, and (2)
From page 79...
... In the early 1970s, de long developed a continuum model for solute transfer in networks of fractures with uniform spacing and infinite length, but a corresponding theory does not exist for the realistic case of finite-length fractures, irregularly located within a rock mass (de long and Way, 1972~. Even less is known of solute transport processes in unsaturated fractured rock.
From page 80...
... Fluid flow laws have yet to be determined for rough-walled fractures, with basic questions to be resolved on the nature of fluid pathways in single fractures and on the dependence of fluid flux on the stress field within the rock mass. Little quantitative work has been carried out on the transport of reactive solutes in fracture networks.
From page 81...
... Spatial Variability and Stochastic Simulation What are the relationships between the spatial structure of medium and flow system variables, such as hydraulic conductivity and fluid velocities, and the geologic processes forming soils, unconsolidated sediments, and rock units? Spatial Variability and Geostatistics One of the key advances in subsurface hydrology over the past decade has been the incorporation of the spatial variability of the hydraulic properties of porous media into our theories of fluid flow and solute transfer.
From page 82...
... This latter situation is frequently the case in studies of deeper ground water flow systems. Measurements of fluid pressure and the collection of representative water samples can present significant technical challenges, especially in deeper boreholes and in lower-permeability systems.
From page 83...
... Stochastic Analysis and Prediction Uncertainty Solutes that enter a ground water flow system are carried away from the point of entry in the direction of ground water flow. This process is known as advection.
From page 84...
... Studies of the variance of a random function under conditions found in subsurface environments are needed to establish the criteria for equating a measured transport property with its ensemble average. What kinds of field experiments are needed to assess the calibrations and predictive application of stochastic transport models at length scales of 100 to 1,000 m?
From page 85...
... Dealing with the Complexity of Reactive Solutes Although there has been growing appreciation of the effect of the "unmappable" heterogeneity of water-bearing strata, much of our understanding of basic subsurface processes depends on our still rather imperfect capability to quantitatively analyze solute transport under homogeneous and piecewise-homogeneous (i.e., "mappably" heterogeneous) circumstances.
From page 86...
... ~ ~ ~ ~ ~ ~ :. ~~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ :~ ~~:~cown~s~:~n~:~a~n ~obse~rvat'~o~n~wel l~nea~r:~pump~:i~g Apt .: HA rnetho;~i~s~se~d:~: ::~ : :::: ~ ~ ::: :::: : ::: : ~ ::: :: :~:: :::: ~ :: :::::: ::::::: :::~:: :::: ::: ~ :::::: ::: :: :::::: ::: :: :: :::::: : ::::: I: :: :::: :::: :::: ;~ ode mat ,~e~m:~6t'~c~a So :ution~th~e~appropriate:~boanda~ pry: ~:~ it Hat bier Developed any Analogy ~~with~:~e~ a:vai:l~l~e~ heat flows: solutions :: ::::::~::: :: ::::::: :: :::: :::: :: ::: : : :~ ~ ~~ : :~ :: ::: :::::: :::: :: ::~: ::~ :~ If: , ~ , .
From page 87...
... Methods for describing solute transport in geologic media have had to outgrow their roots in chemical engineering and other nonhydrologic sciences. This state has now been reached, calling for special efforts and opening interesting possibilities.
From page 88...
... Microbial ecology under field conditions of severely limited mineral nutrients and energy-yielding compounds has yet to be critically studied. Contamination of Ground Water Flow Systems .
From page 89...
... chemical species that are miscible with the pore water and migrate with the ground water flow as a dissolved aqueous phase, (2) organic liquids that are only sparingly soluble in water and move as a-separate phase through the pore space, and (3)
From page 90...
... improvements In simulation capabilities. HYDROLOGY AND LANDFORMS Introduction Geomorphic processes driven by water shape the land surfaces on which human populations and all other terrestrial biota live.
From page 91...
... The altered earth materials are the hydrologic media that determine how ground water moves, whether rainfall is absorbed by soils or flows over the ground, and how chemicals (including pollutants) are immobilized or transmitted in percolating waters.
From page 92...
... Adjacent to the Himalayan chain, the vast Indo-Gangetic lowland is composed of alluvial landforms (including channel bars, floodplains, river terraces, FIGURE 3.5 Channel network formed by ebbing tide in the Gulf of California. SOURCE: Photograph by Anne Griffiths Belt.
From page 93...
... As a land surface is eroded, water is concentrated along depressions either by surface runoff from higher parts of the landscape or by ground water discharging into the depressions. The result is a stream network in which water flows faster and deeper than over the surrounding landscape and has a greater capacity for transporting sediment evacuated from hillslopes.
From page 94...
... Perturbations of the water or sediment fluxes from the drainage basin, as a result of environmental change or human activity, cause changes in channel and valley floor characteristics, often with widespread effects on human habitat. Some Frontier Topics Prediction of Landscape Evolution Most geomorphological research has been aimed at understanding the nature and chronology of landscape development, and it has yielded many important insights concerning the large-scale form and dominant erosion processes of most of the earth's regional landscapes.
From page 95...
... ._ ~ St. Louis FIGURE 3.7 Annual discharge of suspended sediment at six stations on the Missouri River and two stations on the Mississippi River showing the effects of reservoirs on downstream sediment loads, 1939 to 1982.
From page 96...
... Both the understanding of mechanics and the capacity for prediction of geomorphic processes decrease as one moves to interactions between processes on larger scales, but the problems and prospects are exciting. For example, research on the exchanges of water, sediments, and nutrients between river channels and their floodplains is in its infancy, despite long-standing assumptions that the fertility of floodplains is the result of nutrient-rich sediment from certain favorable rocks.
From page 97...
... Prediction of landscape-scale erosion and sedimentation requires viewing landforms in a wider context, including soil and vegetation covers. Changes in the condition of land surfaces therefore depend on the link between erosion and the regional soil-water balance, vegetation cover, and land use.
From page 98...
... 98 lo lo lo Cal 11 o o ._ V' U)
From page 99...
... Competition for runoff, and therefore drainage area, between growing channel networks leads to a land surface that is differentiated into hillslopes and channels connected in a regular, dendritic, spacefilling pattern. The change of the sediment transport mechanism from hillslope to channel may be modeled through the attainment of a threshold value by the function describing the mechanics of the particular erosion process (such as surface erosion, seepage erosion, or mass failure)
From page 100...
... in Venezuela and Kirkby (1976) in England, it was shown that the topology and geometry of the channel network are intimately linked with the hydrologic response of drainage basins and particularly with the flood hydrograph that results from storms occurring over the basin.
From page 101...
... Moreover, a physically based determination of these scaling exponents is expected to identify some general physical principles, e.g., uniform distribution of energy expenditures in channel networks, as a basis for discovering the signature of river basin dynamics in the geometry of channel networks. Investigations outlined above involve only the spatial variability and neglect the issue of time.
From page 102...
... In some localities, chemical tracers and isotope distributions also provide information about sources of sediment and rates of accumulation. If anthropogenic disturbances cause future climatic changes with rates and magnitudes at least equal to those in postglacial times, it is reasonable to anticipate that there will again be widespread alterations of the vegetal and hydrologic condition of subhumid land surfaces, and changes in the magnitude of hillslope erosion relative to the sediment transport capacity of trunk streams.
From page 103...
... SOME CRITICAL AND EMERGING AREAS 103 ; ~ ~ ~ : ~ :: ~ ~ : : : :~ ~ : ~ : it:: : ::~:: :~ :: :: ~ ::::: :~: '~n:~::~:v:~:rs:e ~~:~:~ - rn:_~ :~ :: ::: :: :~: :~: :: act: I: :: : : :: : :: ~~;~YC :^An , .
From page 104...
... improved understanding of the interaction between the hydrologic cycle and the general circulation of the coupled ocean-atmosphere system, and (2) eluci
From page 105...
... A comprehensive approach involving both observation and modeling of the coupled ocean-atmosphere-land surface system is essential for the effective study of climate. Some Frontier Topics Diagnostic Studly of the Global Water Balance How can general circulation models simulate the quantitative structure of the global hydrologic cycle and help to evaluate its effect on climate?
From page 106...
... of the processes involved in the hydrologic cycle is essential for successful general circulation modeling. To the hydrologists, GCMs offer a fresh approach to two main principles of hydrologic science—the hydrologic cycle and the water balance.
From page 107...
... Both the reduction of precipitation and, to a lesser extent, the increase of potential evaporation further deplete soil moisture from the dry continental surface. This description indicates that the land surfaceatmosphere interaction has a positive feedback effect on the aridity of a continent.
From page 108...
... 108 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES ~ :::: ~ ~ :~ 1~ ~~ ~:~:A:I:MOS~PH~ERIC:~ GE:NERAL:~::CIRC~U~LATION~MODE;ILS~ ::~I ~:~ : ~ ~ :~:~ ~~:~ ~~:~Ear~ly~:~:~in:; then twentieth century,: ~L.~:~:R~i~6hardso~n ~~p~ro-ppsed~th~,~s~ince~ :~:::~the~ ~atmos~pfie~re ~ isle ~:~a~m~wi ng ~ fl uid~ ~:~: its motions ;~cou lo pred~itl:ed Phi nag. ~:~e~:basic~:~equati~ons:~of :hy:d rod~ynam~ic~s.~ ~ Un:fo~nately j~th~e~:sh~er~s~ize~:~ i:: ::::~th~e~ p~rob~le~m~:m~ade: ~th~e~:~::num~be~r ~:of~::~n~ecessa~:ry~c~altu~J:~ation~s:~:~to~o:~il~a:Fge:~to:~be :: : ::: ::~ : :::: :: :: :: :: :: :: : ~ ::~ ~ ::::: ::~:~ ~~ :: :~: :~ : ~ an: amp:: :~: i: ~ca~r~ri~ed~0ut~:~ desk :~:c~a~Icu~I~ators~ At i: the:~ti~me.~:~:~After ~:W0rId: :~:W:a~r~ II~,:~:t~hk ~~:~:~ ~:~dev~lop~men~t ::~of~eleŁtr~onic~comp:ute~rs~ v~in~c~reased ~~the~calcO~l:a—~~; :~ :~ bower ~~th~at~:~::c:ou lode directed: to ~ ~solvt~:n~g ~~me~eq~u:at:~ons:~nt~atmos:pher:~Ec~ :: .
From page 109...
... For the validation of a climate model, it is also necessary to determine more accurately the thermal and water balance of the global atmosphere and the exchange of energy and moisture between the global atmosphere and the land, ocean, and ice-covered surface based on the comprehensive observations from satellite and ground stations. One of the main objectives of GEWEX is to accomplish this by a comprehensive strategy combining both observational and modeling approaches (see Chapter 4~.
From page 110...
... 110 6 8 O 4 eC o LL 2 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES 8 · e · · ~ · O 04 ~ ;S~; o 90 60 30 0 -30 -60 -90 LATITUDE (degrees)
From page 111...
... 1983 by the American Meteorological Society. the global water balance and its variability requires accurate assessment of both reservoirs and fluxes.
From page 114...
... 4 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES : I: ::: :FRO:M::~D:ES~E~RT TO:iRAlN:~FO~R~F~r~:~ :: : :~ ~ :: ~ ~ ~~ ~~:~ Aver ~~rece~nt~geol~ogic-~:~:t~l~me~l~ghl~y visible changes: i n Other global water :: I ::: : : ~ I:: ~ ~ : :: I: :: ~ 1: : ,:: ::: :' : : : : : : : ~ :: ~~ Ail: gal ~ance~na~ve occurrence ae~::rl~se~:~:anc ta Tots Sea :~ Never ~ it lies a Vance And I i: ~~retreat~:~of~cont:i~nental~; :~ :ice~ s~h~eets,i~and~:~:th~e~ formation land ~Ide:sicc-~ation~ 0 f I major bakes and ~~ waterways. ~~:At~th~e::~ ::peak~:~:of:~:~:the last;:~:: :Ice~:~ :Age,:~ some ~~ ::: ~ ~ : :::: :~ ~ I:: :: ~1~8~000 y:e~ars:~ago,::~when::a~s far::south~:a:s ~Ke~ntuc~ky~:s:om~e:~:1 500 m of i:ce~:: ~ .
From page 115...
... , soil moisture, ground water, and evaporative fluxes have been relatively neglected. Advances in technology are badly needed in these cases.
From page 116...
... The boundary forcing is exerted as the fluxes of heat, water vapor, and momentum between the surface and the atmosphere. It is influenced by the fluctuations of sea surface temperature, soil moisture, snow and ice surfaces, and vegetation.
From page 117...
... A1though the mechanisms of this interaction lie outside the committee's definition of hydrologic science, the results of the interaction are crucial to the hydrologic cycle at global and regional scales. What is the interactive relationship among rainfall, cloudiness, soil moisture, surface temperature, reflectivity, and vegetation cover?
From page 118...
... suggested that land surface plays the decisive role in the droughts that plague the West African Sahel. He noted the increase of surface albedo that results from the deterioration of vegetation, caused by overgrazing, and theorized that intensive desertification in the Sahel might have been responsible for the reduction of precipitation in the early 1970s.
From page 119...
... Most of the evidence for land surface influences on such largescale climatic anomalies has come from numerical modeling studies. Thus far, the only strong observational support at the regional scale derives from studies of snow cover, an extreme case of land surface change.
From page 120...
... 20 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES ~;~ ~ ~ ~:~::~GRE~J~HoitSE~IGASE:S~A~N~D ::~Ł LOB~AL ~ ~HYOROL~OG~Y :: : :~ ::: : ::: ~:~:~ ~:~:l~ne:~atm~osp~re ::~con~ta~i~n~s: ~va:r~i~ous ~t:race~:~ ~aa~ses~. both::~ n~at~r~l~:~:~n~fl~ ~mA:n- ~: :: >ac~:~that~effecti~vely~trap ~:tlie~o~ptgo~ n~g~ ~ te~r~strl~a 1~ :~ - iation:~ ~a~nd~:~::warm :~:~ ~:~ the~cli:mate.:~Si~nce :the~ ir duistr~i:a~l~Revolution~,~;:~concentra~ti~ons~of some~of ~::~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ , ~ ~ ~ ~ ~ ~ ~ ~ : ~ ~ - , e s e ~ ~ ~ s o - c a ~ l ~ e a ~ ~ ~ ~ ~ g r ~ e e i n ~ 1 0 u ~ s e ~ ~ ~ ~ ~ g ~ a s e s ~ ~ ~ : S U ~ Ł ~ ~ ~ : a s ~ ~ c a r 3 0 ~ ~ n ~ ~ ~ : ~ ~ c ~ ~ i o x i d ~ e ~ ~ ~ m ~ e t h a ~ n e ~ , ~ ~ ~ : n i - ~ ~ ~ : : : : ~:u~s~ogiJe,~a~nd~l~c~hiovfluorocar~b~ns ~h~ave~ been~incre~sin~:st~ilu; n :~ : ~ne~: ~:~rmospne re.~ ~ '~ ~ ~tne ~esen t~em~iss i on ~:~rates ~: ~co~n ti~n u e~,: :~ ;tl~:~:~com b~; ned~ ;:~:~:~:~ I :: ~:::::~:: ~: :~ ::::~:~: :::~ :::~ : ~::: ::::: ::::: - ::::: ::::: :::~ :~ :~:~ ~ ::~ :~:~ :: : ~ ::~ :~ ~ ~t: ~e:~r~m~a~ ~ totci~tro~m~:~atrn~pheric~carbon~diox~ide:~a~nd ~: other ~ green~hou~s~e:~:~:~ : ~:~gases~:id~entified ~:above~cou~ld:~doubl~e~from~:th~e~ prei~ndu:strial ~:l~evel~s~ometime~ ~ :~ ~:~d~ip~e~ ~fi:r*
From page 121...
... A high albedo over a significant portion of a continent has a profound cooling effect on air masses in What are the physical factors that control the snow coverclimate feeciback process and its role as amplifier of climatic change?
From page 122...
... The cold air mass flows out of the Arctic and reaches and interacts with the surrounding, warmer water bodies. The cooling effect of snow cover also increases the summer-winter contrast of surface air temperature in high latitudes.
From page 123...
... When the nearsurface temperature of the atmosphere drops, a larger fraction of precipitation falls as snow and the melting of snow becomes less likely, resulting in expansion of the snow-covered areas. Because of the increased reflection of solar energy from the expanded snow cover, the sensible heat flux from the earth's surface to the atmosphere is reduced, further reducing the surface air temperature.
From page 124...
... 24 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES ISI~ ~i~rr~ru~n4ff~ TO pi ls~j^~ Invest-: Id wit: _ ~~I—~~ma.s:;es Em ~p ~d: i: [= ur~; ~ eat ~~ ~
From page 125...
... Remote sensing offers many possibilities for data collection that should be fully exploited to gather information about the snow cover over the large scale of interest for snow-climate studies. The use of remote sensing includes measurements of fundamental interest to snow hydrology such as snow-covered area and, more recently, the possibility of determining albedo directly.
From page 126...
... 126 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES : I:: ~ Ail: of: ~~T~H~o~NT:~WA~lT~E~ :~ :~ ~~ ~ ~ ~ ,,_ ~~ ~~ s~ ~ ~ .~ ~~ I: : I: ~ ~ : :~ :: ~ :f~1~:Q~_:~1~:~::~ :~ ~ ::~ ~~ :~ ~ ~ : ~:~::~::~:~:~i~W~a-r~re~n~T~ho~r~n~th~w~a~i~td~h~as~:~b~ee~n~:~:~d~e~sc~r~:i~bed~:~by~:::~s~om~e~:p~ee~r~s:~as~:~"th~e~mo~st ~influ~e~ntial~climamlo~ist of ~ hilt ~eene~rat::i~on."~ ~This: ora~lis~e~w~as ~:earn~ed~in~ ;~ ~~pa~rt~i~r~ h~is~fu~n~dame~nta~l~stu~diies~ into Ethel n~atu~re~of~ev~aporation~ ~an:d~h;~s~ ~fo~rm~u:~la~t~'o~n~ of~the~concept~of~potential eV~a~potran~s~pi~;rati~o~n~:,~:~for~h~i~s~ out-: :~ I: sta~d~ing~l~9485~ paper ~~An~:Approach~ Towards ask Rati~onal:~l~as~sifica~tio~n:~ of ~CIimate '' Air his establishment of the~Laboram~CI imato~l:o~r~at ~Sea~b~o~k~ ~~:~ New Jersey ~ which Became acid m~ecca~r~c~limatologists And hydrologists ~~:~ From All: ~~pa~s:~:~of i:h~e~wo:r~ld~ ~~ and his Early ~lea~dersh~i~p~of~th~e ~~ World Aim: ~:eteoro~Io~ical~ ~~O~r~an~zat'~on~is~Com~m~s~sion Or Clim~atoi~o~v:.~ ~~ ~~ ~ ~~ = ~He~hi' ~ Early ~~ ~~ :: ~~:U~nliversity ~i~(th~e:n:l~l:a:l~te~ac~h~e:r~s' ~ co:lil:~e~ge) ll li~n~l~ :~1 ~:9~2211~a~n~d ~~ Undertook:: ~so:m:~ell~g~radu- ~ :~:: l Mat work at The ~Un;~vers~ity~of~ Michigan before moving onto ~th~e~De~pa::rt-~ meant of ~~ Geography at the tLJniversi~ty~of~ Ca~l~i~lb:rn~ia, ~~ Berkeley:, ~ where he ;~c~a~m~u~n~;d~er The Influence Of ~ ~~Car~::~Sa:ue~r~a:~n~d ~ gra~d~-u~ated~:~:w~i:~h A Ph.
From page 127...
... To understand the climate or even short-term weather patterns of a snow-covered continent, it is necessary to understand a wide range of the physical properties of snow and to use these to determine the boundary conditions for models of atmospheric circulation. HYDROLOGY AND WEATHER PROCESSES Introduction Of all the processes in the hydrologic cycle, precipitation in all its forms probably receives the most public attention.
From page 128...
... Humaninduced changes in land surface characteristics are accelerating around the globe, and thus it is urgent to understand the influences of land surface processes on weather and climate. Once again, we stand on the threshold of a time in which a new array of tools, notably remote sensing of the land surface from satellites, in combination with targeted field experiments, promises advances on this challenging and important set of problems.
From page 129...
... Do the resultant changes have an impact on weather? Statistical studies have established the role of land surface characteristics in determining mesoscale meteorological patterns and in the development of severe weather events.
From page 130...
... Hydrologists who study processes that govern the surface water balance, and hence evapotranspiration, must consider variations in the properties of soils and vegetation that are important on scales of a few meters, and there are no accepted methods for estimates on kilometer and greater scales. Multidisciplinary studies are under way that attempt to bridge this scale gap by increasing understanding of the fundamental hydrologic processes that can lead to parametric formulations for land surface processes on the 10- to 100-km scale.
From page 131...
... Before we can answer such questions about how alterations in land surface properties can alter weather and climate, and improve predictions of elements of the hydrologic cycle regionally, we must learn how to make quantitative estimates of regional water budgets on both the atmospheric and the terrestrial sides of the interface. We want to know the daily and seasonal cycles of these fluxes and storage terms and their sensitivity to soil and vegetation type, state of growth, and precipitation history, including the effects of uneven distribution of precipitation.
From page 132...
... OPPORTUNITIES IN THE HYDROLOGIC SCIENCES ~~FLASH~F:L~OODS:~ ~~ ~~ ~:~ ~~:~ ~~: ~:~ ~ ~~ ~ ~~ ~ :: ~ ~ :~:::: If::: if::: ~ :~ :: ::: : :: :::::: :~ ::~:: :~:: ~ ~ : ~::~: ~ :: ::: ~ ~~ I:: ~~ ~ :~ ::: at: :~::~::: ::::::: ::~ ~ ::::: :~ ~~ ~ :~:~:~::::::~: :: I:: ~~ ::~: :~:: :: :~:: ::::::: ~~ ~:~::~ :: :: :::: ::~:~:: ~:~::: ~~ :::: ~::~: ~~:~ ::~: : :: ::: i::::: :: ~ ~ ~ ~ ~ ~ ~ .
From page 133...
... The Rapid City, Big Thompson, Kansas City, and Johnstown flood disasters are all examples lacking a significant cyclonic storm or strong front. The apparent paradox extends to tropical cyclones; many powerful hurricanes produce moderate rainfall, whereas some of the worst flood disasters are associated with weak or dissipating storms.
From page 134...
... The convective clouds continue to grow and die along this same line for many hours; the line may be slow or fast moving and may propagate with a velocity different from that of the ambient wind at any level. After some hours, the stratiform precipitation region forms, its water source a combination of water vapor and ice crystals adverted from the debris of the continually dying convective clouds in the adjacent line, and independent mesoscale ascent.
From page 135...
... 50 100 150 FIGURE 3.16 Schematic of the structure of a mesoscale convective system as viewed by radar in horizontal and vertical cross sections during (a) formative, (b)
From page 136...
... There is an important additional factor that must be supplied by hydrologists: what will be the response of the river basin? Improved warnings of flash floods require that better rainfall observations and predictions be coupled with hydrologic models of runoff production on the basin scale.
From page 137...
... SOME CRITICAL AND EMERGING AREAS :/Synoptic Rain Area) al ~ MCS An/ Convective Cells 137 ~ Mean Wind O O / ')
From page 138...
... 138 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES Atmospheric processes at the unresolved scales have to be treated statistically because the information needed to describe these processes is not available or because the physical processes themselves lead to inherent fluctuations at such scales. In this latter case, owing to the nonlinear and turbulent nature of atmospheric flow, even processes resolved by a model have only limited ranges of predictability in the deterministic sense.
From page 139...
... ished ? Preliminary analysis of spatial rainfall data over different-sized regions shows the presence of fundamental structures that are likely to be of great theoretical and practical importance.
From page 140...
... OPPORTUNITIES IN THE HYDROLOGIC SCIENCES 16 to 40,000 km2. This phenomenon suggests that spatial rainfall may not have a unique length scale, for otherwise the variance would decrease as A-~.
From page 141...
... . Copyright ~ 1987 by the American Geophysical Union.
From page 142...
... Between rainfall events, there is a continuous return flux of the water available at the surface to the atmosphere in the form of evaporation. Clearly, mass transport of water is the common denominator of these surficial processes in the hydrologic cycle.
From page 143...
... The state of the art of accounting for and describing surficial processes holds both formidable challenges and unique opportunities. One theme common in the hydrologic literature today is that it will be possible to describe the global hydrologic cycle only when we understand the relationship among relevant hydrologic processes on different temporal and spatial scales.
From page 144...
... The retention of soil moisture and the attendant runoff from naturally occurring rainfall, snowmelt, or irrigation are fundamental processes upon which civilization depends for food production, potable water, and navigable streams and waterways. Infiltration the process that partitions precipitation or irrigation into that part temporarily stored in the soil and that part remaining on or flowing over the soil surface depends on the soil, its relief, and its management.
From page 145...
... Deterministic models of infiltration and unsaturated soil water flow are giving way to spatially stochastic concepts. Interest now centers 1o2 ~ _ I 1o1 1 PLOT 1 / PLOT 2 I ~ ~ I .1 0.3 0.4 0.5 SOIL WATER CONTENT (cm3 cm~3)
From page 146...
... on the value of the unsaturated hydraulic conductivity (K)
From page 147...
... Indeed, multiphase flow including the migration of partially miscible and immiscible fluids offers a challenge to the hydrologic community that only recently emerged, albeit in the form of a practical problem resulting from ground water contamination. Runoff Production by Precipitation One of the major difficulties in understanding and quantifying runoff generation in river basins stems from the presence of spatial variabilities in topography, geology, soil type, and vegetation, as well as in climate fluxes such as rainfall, infiltration, and evapotranspiration.
From page 148...
... More recently, however, questions have arisen concerning the acidification of streams and the contamination of ground and surface waters by pesticides, herbicides, and fertilizers, which have underscored the need for the investigation of the spacetime structure of river runoff to the channel network as a result of rainfall and snowmelt. This need has intensified debates about each process of runoff generation at the smallest contributing catchments, such as the role of flow in macropores, the effect of microtopography and vegetation on surface flow hydraulics, and the relative importance of random and trending spatial patterns in land surface and nearsurface characteristics.
From page 149...
... SOME CRITICAL AND EMERGING AREAS ~~ ~~-~ ~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ Ether Uses. ~ -diversion -~w-=r~not~on~ ~~mod~ifi~es~th~e~ori~gin~al~e~asystem~, ~~ ~ tS~ ~ ~ ~ :~ ~; ~ :~ ~~: ~ ~~ ~ ~~ ~ ~: ~ T: ~ ~ :~ :~ ~~ ~~ :~: ~ ~ ~ :~ ~~ ~~ ~ ~ .
From page 151...
... Evaporation is a major component of the hydrologic cycle, as on a global basis its temporal average is equal to that of precipitation. Even on the land surfaces, it still amounts on average to about 60 percent of precipitation.
From page 152...
... The partition of the available energy at the earth's surface into evaporation and sensible heat flux is dictated by the nature and the state of the vegetation and the attendant soil moisture stresses. In spite of the importance of the problem, in current hydrologic practice there are no operational methods available to measure, forecast, or otherwise determine the actual evaporation from river basins.
From page 154...
... How do surface radiation balance and boundary layer dynamics control land surface evaporation at the mesoscale? The region of the atmosphere that is most directly affected by the land surface is referred to as the atmospheric boundary layer.
From page 155...
... and suitable formulations for the boundary conditions, including those to calculate momentum, heat, and water vapor fluxes. One component of these GCMs, to which they appear to be quite sensitive, is the proper formulation of the hydrologic budget of the land surfaces of the earth, namely, soil moisture, evaporation, and related variables.
From page 156...
... The hydrology of these cold regions is dominated by freezing and thawing processes and by the presence of ice on and below the surface. Surface water and ground water interactions involve the usual multiphase porous media flow, coupled with heat flow, phase changes, and other complications such as solute rejection, water pumping, and ice segregation.
From page 157...
... The hydraulic conductivity, for instance, depends not only on the physical properties of the soil and the fluid, but also on variables such as temperature and the amount of ice in pore spaces. Ice lenses restrict infiltration during spring melt, influencing surface water runoff and ground water recharge.
From page 158...
... Improved understanding of the snow problem could aid in the solution of the soil problem, as similar processes of heat and mass transfer are involved in both. Many opportunities exist for scientific advancement in this field of surface water and ground water interactions in the presence of freezing.
From page 159...
... · Water resources development in arctic and alpine lands will be aided if many problems caused by freezing can be solved. Water quality is affected by solute rejection during freezing, ground water between or under perennially frozen layers may be under high pressures, and modification of these systems by humans may lead to untoward results unless a proper understanding of heat and mass flow in freezing soils is at hand.
From page 160...
... Hydrology of Snow-Covered Areas The distribution of snow deposition is not uniform, and the processes of snow metamorphism and melt proceed at different rates in different parts of a single drainage basin. Seasonally snow-covered areas of the earth, especially in mountain ranges, are important components of the global hydrologic cycle, even though they do not cover a large portion of the earth's surface area.
From page 161...
... How can we integrate the radiation balance over large areas to provide estimates of times and rates of snowmelt in alpine terrain? In a seasonal snow cover, newly fallen snow is thermodynamically unstable, undergoing continuous metamorphism until melt occurs in the spring.
From page 162...
... The amount and chemical composition of water entering streams and lakes in alpine areas depend on the quantity and composition of atmospheric deposition of water and chemical species and on the hydrologic and biogeochemical processes occurring in the snowpack and in the drainage basin. Understanding these processes requires a coordinated, interdisciplinary effort.
From page 163...
... Thus the principal use of remote sensing of snow in these wavelengths has been to map the extent of the seasonal snow cover. Throughout the world, in both small and large basins, maps of the snow cover throughout the snow season are used to forecast melt.
From page 164...
... , but the application of the findings is essential to solving problems at much larger scalesfrom drainage basins (10 to 100 km) to continents (1,000 to 10,000 km)
From page 165...
... Of critical importance is the mass and heat exchange at the interface between the water and the surrounding atmosphere. Most methods available are based on similarity formulations for the profiles of mean wind speed, temperature, and humidity above the water surface.
From page 166...
... Yet the microphysical mechanisms of evaporation and related transport phenomena from a water surface disturbed by waves are poorly understood. The fluxes of water vapor, sensible heat, momentum, and other admixtures near the water surface are primarily the result of the turbulence in the air, but this turbulent flow interacts strongly with the irregular wave field of the underlying water surface.
From page 167...
... Thus evaporation is a "consumptive" use, and this fact is fundamental to water resources planning and management. The vapor transfer at water surfaces must be predicted as accurately as possible, because such information is indispensable in designing the capacity of storage and flood-control reservoirs and assessing the value of natural water bodies for municipal and industrial water supply, navigation, irrigation, and recreation.
From page 168...
... Moreover, the nature of organic coatings on stream sediments is an important factor in the quality of runoff, which in turn deeply affects the stream biota and all the living communities in the watershed. The hydrologic cycle clearly is fundamental to the patterns of adaptation of terrestrial and aquatic living systems.
From page 169...
... However, as stated in Chapter 2, the committee's definition of hydrologic science is restricted to processes that are significantly interactive with the hydrologic cycle. That is, the biological processes of interest here are not just affected by hydrology but in turn affect hydrology in a significant manner.
From page 170...
... Stepping back from the individual tree and the complexity of its interactions with its neighbors to take a wider view of the forest admits simpler physically based models that can capture the primary distributional features of a given community. For example, modeling savanna vegetation as a tree-grass system where the two vegetation types compete for water and solar energy has provided insight into the conditions for both equilibrium and stability of such communities.
From page 171...
... Since both carbon dioxide and water vapor exchange occur through the stomata, the evapotranspiration rate is often used as the basis for estimating productivity (Figure 3.22~. Optimality Constraints on Vegetation Communities Do adaptive or evolutionary pressures lead plant communities to states of development or to physical characteristics that are in some sense optimal with respect to a critical clirnension of their environment?
From page 172...
... . 1 1 1 1 100 200 500 1,000 2,000 ACTUAL EVAPOTRANSPIRATION, mm/yr FIGURE 3.22 Net primary productivity in relation to actual evapotranspiration.
From page 173...
... transpiration and that this is the so-called climatic climax state of the community. Where vegetation types having similar physiology are present at the same site, competition for resources will occur.
From page 174...
... 174 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES : ::: :: : : ::: ~ i: M~ICH~AE~L:::EVE:IWARI: : (:1 904-11989~) ~ I I ~ :: : ~ Michael Evenari ~ is best~known~ in The field of Plant ecology,~especially~as A :~ ~ _ _ _ :: : _ ~ ~ ~: : A:: :: ~ ~~ : A:: ~ : :::: ~~ ~ Pioneer i n plant ecoph~ysiolog;y,~ but ~~ his~ll~Gareer ~ illustrates l~h~v~imp~ortant:~landl interrelated~hydrology~i~s to~other~fiel~ds.~Evenar~i wasl~rn~in Gerrnan~y~;n~1~904 as; Walter Schwartz.
From page 175...
... Microbial Transformations of Ground Water Contaminants What is the nature of the feedback processes that occur between biochemical processes and the various physical transport mechanisms? Subsurface microbiology and biotransformation of organic contaminants offer scientific and engineering challenges.
From page 176...
... 176 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES ~~:~ ~~:~:~CHARI:ES~:~R:~HU~R~S:H ~~ ~~ ~~:~:~ :: : i:: ::: : i:: :: ~:~895~-~1~ 9Wi~:: ~ ~~ ~~ The ~~\Ve~s~ Ewe ~~Of~l~g~1 1~p~1~r~the ~~establ~'shme~nt~of National ~~ ~ ~ :~ ~ ~ ~ ~ ~: ~ ~ ~: ~ ~ ~ ~~: ~ ~ ~ ~~ ~ ~ ~ ~ ~ ~ ~~ ~ ~ ~ ~ ~~ ~~ ~~ ~ ~ ~: ~ ~~ ~ ~ ~ ~ ~ ~re~i~n~th64~ ~E~a~s(~pri~mar~l~y~to~pr~re~st~a:6d ~~ where rest~r~c~es~i~n h~3Aw~f~rc~::~ ~n:~:v~if,~hl~tr~m~ ~~ :~+P~ti~m~ Little was Own About t~inMl~u~ence~l~rests~o~n~water~t~ld~ing~ ~~a~nd~reg~lat~ion~streamflow~.
From page 177...
... SOME CRITICAL AND EMERGING AREAS 177 IHI~i:s;~:c~on~tr~f:b~u~ti;~ons~to~lth~e ~~h~y~diro~log~i~c~ Sciences l~a~:d~ocum~ente~d:~ :~in~; ~~ ~ Over 1~ ~:p~u~b-~l~catio~n~s~. ~:~ ::rerh~aps: ~t~e~gre~a~test ~trl~u~te~to As ~g~e~nl~u~s~:~l~:s:~ that: ~~ ~~ ~ ~ ~: ~~ ~: ~ ~ ~ ~ ~~ ~ ~~ ~ ~ ~ ~ ~: ~ ~ ~ ~ ~ .
From page 178...
... HYDROLOGY AND CHEMICAL PROCESSES Introduction Chemical processes in the hydrosphere determine the composition of natural waters, control rates of chemical weathering and the geochemical cycles of most elements, and influence the chemistry of both the earth's crust and its atmosphere. Trace atmospheric gases emanate in large part from aquatic and wetland systems, influencing climate and hence the hydrologic cycle itself.
From page 179...
... Hydrologists will need to focus more on the actual pathways and residence times of individual water parcels in different environmental compartments. A1though many traditional problems in hydrology (e.g., large-scale water balances, flood forecasting, and ground water resource evaluation)
From page 180...
... Research using rainfall composition data as tracers of the hydrologic cycle offers opportunities to understand better the
From page 181...
... However, it has only been during the last two decades that analytical facilities have been capable of demonstrating the great variety and range in concentration of substances included in precipitation. Gases, liquid droplets, and particulates are released into the atmosphere from natural and anthropogenic sources on the land surface.
From page 182...
... 182 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES thy ~~ ~~ ~~ ~~ ~ ~~ ' ~~ ~~: ~ ~ ~~ ~~ ~~ ~~' :~:~:~::~: ~ :: ~~:f~d~D~may~h~ave~ ˘r~the~:~n~aturai~ro-~ ~:~ 'if ~ ~ ~~ ~ .: ~~ ~ ~ ~~ ~ ~~ :~ ~~ ~~ .~ ~~ ~ ~ ~~ ~ ~~ ~~ ~ ~~ ~~:~ ~.:~.
From page 183...
... As the seasonal snow cover thickens with the included impurities,
From page 184...
... Thus the events during any particular winter can have a considerable effect on the details of an acid flush. Large variations In the chemical contamination of snow occur vertically over the scale of the thickness of snow cover and laterally over the regional scale.
From page 185...
... Quantitative ignorance of these pathways is a major obstacle to understanding the chemistry of the water when it re-emerges as streamflow. Weathering, microbial transformations, production of humic materials, and plant uptake profoundly influence subsurface water chemistry; yet, models of each are in their infancy.
From page 186...
... ~ ~;;;, | Polymers | Mineral Weathering FIGURE 3.28 Some physicochemical factors controlling the acidity of water in soils. The close interaction of both chemical and hydrologic processes is involved in the ultimate determination of soil water chemistry.
From page 187...
... Contaminant Fate and Transport The frontier issues in ground water and soil water contaminant fate and transport share much with the issues of subsurface acid deposition effects described earlier. Usually, however, the chemicals of concern issue from point sources.
From page 188...
... Clay minerals themselves carry adsorbed ions that can be exchanged with other ions in solution, thereby affecting water quality. Thus one must understand sediment-solution interactions in order to understand the chemistry of surface waters.
From page 189...
... . This means that a surface water system can develop a significant "memory"; therefore a common simplifying assumption, that adsorbed solutes are transported almost entirely in dispersed fine-grained sediments, can be very wrong.
From page 190...
... Global Chemical Cycles What are the feedback links that control the interaction between the hydrologic cycle and the global chemical cycles of crucial elements, such as carbon and nitrogen? Several elements have biogeochemical cycles that are important at the planetary scale and are linked to the habitability of the planet as well as to the distribution and productivity of its ecosystems.
From page 191...
... An example is the problem of methane release from wetlands. Methane gas follows water vapor and carbon dioxide in importance as a greenhouse gas.
From page 192...
... So o o by= 1. Methanogenesis FIGURE 3.30 Processes involved in methane evolution from northern peatlands.
From page 193...
... SOME CRITICAL AND EMERGING AREAS 193 _ :: ::::~:: :: : ::::: A: If: ::: ::~: ~ ::::: :: ::~ :~ ::::: ::::: :::: i: :: :: :~: ::~ ~ :~: ~ i:: ::::~: ::::::: ~ ~ ::::: :: ~ : ~ :: :::~::: i:: ::::: :::: :: ::: ::~ :~::::: ::: ::: ~ :~ :: :::: : ::::: i: ::~ ::: :~ ~ : :::: :: :~ : i: : :::: : ::: : ::: ~~ :: ~ : :: :: ::::: ~ :: :~: : : :: :: :~:::~:: ::::~: : ::::: ::::: : :: :: ::: : ::: : :: ::: :::::::: ::::::: :: :: ::: :: :::::: : ::: ~ : ~ ::~: :::: :: :~: :::: : :: : : ::: : : i: : : ::: : ::: :::: : :: : :: :: : :: :::::::: ::::: ::::: :::::: ~ :::::: :~: : :: i:: :: :::::: ~ ::~: :: i: ~ : ::::: : : ::: ~ : ::: :::: :~ ::: :: :: :: : : ~ :: :: ::: :::: :: :: :: ~:~:::::~:~: :::: ~:~:~:~ aft: :~: ~~: :::: ~ ~~ ~~ : ::::::: :~ :: ::::: ::: ::: :~: :: ~:~ ~ :~^R:~:~T~:::~: ~~ ~ A~:~::~I: ::C:~:: :: ~ :: i:: :~ : ::: ~ :: :: .
From page 194...
... The early attempts at a quantitative understanding of hydrologic phenomena were directed toward laboratory experimentation of individual processes, for example, water movement over land, in channels, and into and beneath the surface, and their mathematical characterizations. These efforts led to a fairly comprehensive laboratory-based understanding of many individual components of the hydrologic cycle.
From page 195...
... In this section, some of the emerging new directions in theoretical investigations of hydrologic phenomena are described to illustrate the ideas and objectives listed above. Some Frontier Topics Scaling and' Multiscaling Invariance in Spatial Variability of Hydrologic Processes "This paper is an invitation for the reader to solve the problems of pure and applied geometry involved in its approach to the notion of length and shape rather than an attempt of the author to answer the questions by himself." So reads the abstract to the classic paper by Hugo Steinhaus (1954)
From page 196...
... In his paper entitled "Erosional Development of Streams and Their Drainage Basins: Hydrophysical Approach to Qualitative Morphology," Robert E Horton (1945)
From page 197...
... The search for an invariance property across scales as a basic hidden order in hydrologic phenomena, to guide development of specific models and new efforts in measurements, is one of the main themes of hydrologic science. Modern approaches to problems in hydrology are moving toward scaling theories as much out of pragmatic necessity as out of pure scientific curiosity and rigor.
From page 198...
... If the spatial and/or temporal variabilities embody a fundamental hidden order that manifests itself across a wide range of scales as an invariance property, then it must be formulated mathematically and tested empirically, for the presence of such a property must be obeyed by more specific mathematical models. Recent investigations of the scaling properties of river networks have provided new theoretical insights into the widely known empirical feature that, on the average, rivers drained by larger drainage basins have flatter slopes than those drained by smaller basins.
From page 199...
... On the application side, such theories will guide hydrologic predictions for river basins under sparse data sets, and due to anthropogenic changes, as well as aid in the development of fundamental mathematical models of the hydrologic phenomena. Stochastic-Dynamical Analysis of Hydrologic Time Series An important task in hydrology or in any other branch of natural science, for that matter is to reconstitute from the data the principal features of the underlying physical system and to make predictions about its future evolution.
From page 200...
... Nevertheless, the traditional statistical analyses are not always telling the whole story, and it is important to adopt complementary approaches that are based on a more dynamical view of the hydrologic phenomena. The importance of a dynamical approach stems from recent developments in physical and mathematical sciences.
From page 201...
... This view is reminiscent of a great number of natural processes. For instance, it has been used recently to model the principal features of the abrupt climatic changes associated with Quaternary glaciations.
From page 202...
... However, once the system lands in either of these states, it is still subjected to variability arising principally from two sources. The first one includes the imbalances that inevitably exist between such internally generated processes as transport and radiative mechanisms, and the second source arises owing to disturbances of an external origin, such as the sea surface temperature anomalies.
From page 203...
... This intermittent evolution looks very much like the record of Figure 3.33. More generally, it provides us with an archetype for understanding other hydrologic processes beyond our specific example, for instance, river flows that seem to exhibit abrupt transitions.
From page 204...
... New physical insights and predictive capabilities will emerge from such analyses in the future. Nonlinear Dynamics and Predictability of Hydrologic Phenomena Weather and climate processes of hydrologic interest, such as rainfall, exhibit a complex and highly variable structure in time and space.
From page 205...
... SOME CRITICAL AND EMERGING AREAS Are there strange attractors in hydrologic time series? What are the limits of preclictability of hydrologic phenomena?
From page 206...
... 206 OPPORT~ES ~ ME HYDRO[OGIC SCONCES so :~ I?
From page 207...
... These techniques hold the potential to enhance understanding of different dynamic scenarios in diverse hydrologic processes, e.g., river flows, sediment flows, and rainfall, which is necessary both for developing physical descriptions of these processes and for making predictions. SOURCES AND SUGGESTED READING Hydrology and the Earth's Crust Back, W., and R
From page 208...
... 1986. Statistical theory of ground water flow and transport: pore to laboratory, laboratory to formation, and formation to regional scale.
From page 209...
... 1981. Satellite Observations of Variations in Northern Hemisphere Snow Cover.
From page 210...
... 1975. The seasonal variation of the hydrologic cycle as simulated by a global model of the atmosphere.
From page 211...
... 1982. Land Surface Processes in Atmospheric General Circulation Models.
From page 212...
... 1979. World Water Resources and Their Future.
From page 213...
... Erosional development of streams and their drainage basins: Hydrophysical approach to quantitative morphology.


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