an orderly scheme to systematically examine and analyze the movement of water through the landscape
Global Scale
depicts cyclical movement of water between oceans and continents
a closed system since all water fluxes are transfers, the global scale encompasses all sources and sinks of water (they are internal)
generalized so it is only useful to illustrate the basic concept of a water cycle and global distribution of water (storage capacities)
Global Distribution of Water - the major phases of the hydrological cycle
surface storage (rivers, lakes)
0.02%
glaciers
1.9%
groundwater/ soil water
0.5%
atmosphere
0.0001%
oceans
97.6%
60% of river water in Amazon and Congo
about 8% of Canada is lake (largest area of lake in the world)
global precipitable water vapour = 25 mm; global average annual ppt. = 1000 mm, therefore, atmospheric water is completely recycled 40X per year or every 9 days
Regional Scale - Basin Hydrological Cycle
more common and useful scale
depicts the movement of water among storage places for discrete areas of the earth, for example ecosystems or most often drainage basins
drainage basins are by definition closed to inputs of surface water thus the number of inputs is minimized or essentially reduced to one, precipitation, although interbasin transfer of groundwater may occur, but is difficult to quantify and generally assumed to be insignificant
outputs from drainage basins are by evapotranspiration, flow at the mouth of the mainstem stream which ultimately accounts for all runoff, and possibly output (seepage) of groundwater
Limitations of the water cycle concept
descriptive and conceptual, components are not readily quantified
implies smooth (constant rate), continuous (a complete cycle), and
sequential (a distinct order) movement of water, and uniformity over time and space
thus a simple graphic depiction of the water cycle tends to be
misleading, given the large temporal and spatial variation in the distribution and fluxes of water
does not portray variation in timing and magnitude of flow and storage,
but it does capture the spatial distribution of storage zones and processes linking them, and therefore is particularly useful in geography
A Systems Approach
System
an aggregation of parts united by regular
interaction, e.g. a internal combustion engine, an ecosystem
Hydrologic System
components of a landscape or basin that store water (vegetation, soil, rock, depressions, glaciers, etc.) and interact in a regular way according to the
physical principles that govern the state (liquid, solid, gas), movement and storage of water (gravity, thermodynamics)
The hydrological system is expressed in terms of inputs, outputs and throughputs (transfers). The definition of these depends on the definition of the system, that is,
whether it is an entire basin or a subsystem such as a specific storage of water. No sequence of water flux is implied, rather all interactions and degrees of temporal and spatial variation are accommodated provided they obey physical principles. Storages and linkages can be assigned certain coefficients which reflect physical controls or flow rates and storage times characteristic of particular
environments.