Center for Research in Water Resources
The University of Texas at Austin
This is the third version of the Digital Atlas of the World Water Balance.
Previous versions of the atlas presented on GISHYDRO 97 and GISHYDRO 98
have featured a compilation of global climate data, in GIS format, for
use in characterizing the water balance of the earth. The data and other
materials contained on the previous versions of the Atlas can be accessed
online by clicking on the respective links below:
GISHYDRO
98
GISHYDRO
97
In this version, the emphasis is shifted from the characterization of vertical processes to the characterization of horizontal processes affecting the movement of water over the land surface. The data presented in this atlas are intended for use in continental scale runoff routing and other large scale modeling applications.
The National Center for Atmospheric Research is working with a number
of universities and other research institutions to develop a better understanding
of global climate. An important part of this research is the development
of a fully coupled climate model incorporating all phases of the global
hydrologic cycle. These models, commonly known as General Circulation Models
(GCM), are continually being refined with a view to improving our understanding
of the earth's climate. Runoff generated in the the land surface component
of these models is currently being transferred to the ocean with little
or no routing. The development of a global database of routing parameters
will allow for the inclusion of more sophisticated routing procedures in
the models. The data presented in this version of the digital atlas have
been processed as part of that process.
Drainage Basins
The drainage basins presented in this Digital Atlas are delineated
for sections of coastlines. These sections are in turn defined by intersecting
the continental margin with a 3 degree by 3 degree mesh. While these basins
may in fact correspond to the outline of a single river basin, this is
not necessarily the case. They are delineations of the portion of land
draining to the section of coastline or ocean defined by the each 3 degree
mesh box. The data are presented in the form of compressed Arc Info coverages.
Refer to the Terrain Analysis
documentation on drainage basins for more information and images.
Modified Terrain Grid
The modified terrain grids are derived from the original DEM by projecting
into a lambert azimuthal projection, inserting sinks in inland catchments
and filling the resulting grid. The DEM cannot be used in its original
state because it contains sinks which curtail the flow of water. By filling
in any unwanted pits, a modified terrain grid is produced in which water
can flow uninterrupted over the land surface. The data are presented in
the form of compressed Arc Info grids. Refer to the Terrain
Analysis documentation on modified terrain grids for more information
and images.
Flow Direction Grid
The Flow direction grids resolve the flow in each cell into one of
the eight compass directions. Each grid cell is assigned a value of 1,
2, 4, 8, 16, 64 or 128 for a downstream flow direction of east, southeast,
south, southwest, west, northwest, north and northeast, respectively. The
directions are assigned based on the simple premise that water flows downhill
and in the direction of stepest decent. Refer to the Terrain
Analysis documentation on flow direction grids for more information
and images.
Flow Length Grid
One of the key factors in determining the shape of any flow hydrograph
is the distance that incident moisture travels to the measurement point.
The flow length grids are a useful source of this information. They provide
the distance that water from a given cell would have to travel to get to
the basin outlet. Travel times can be computed from flow lengths by dividing
by flow velocity. The flow lengths are reported in kilometers on this CD-ROM.
Refer to the Terrain Analysis
documentation on flow length grids for more information and images.
Flow Accumulation Grid
The flow accumulation grid is a measure of the number of cells upstream
of a given cell. Since the area of each cell in this data set is one kilometer
squared, the value in each cell is exactly equal to its upstream drainage
area. Flow accumulation grids are particularly useful in hydrologic model
because they are required inputs for a number of GIS delineation processes.
A river network can be derived by specifying a minimum drainage area for
the formation of a river. Watersheds can also be derived from flow accumulation
grids. The grids presented on this CD-ROM are in the form of Arc Info integer
grids. However, these flow accumulation grids do not contain value attribute
tables (.VAT). VATs are required for some Arc Info commands but their
inclusion in large DEMs causes the grid to increase in size by a factor
of 3 or 4. Use the Arc Info Grid command BUILDVAT to create a VAT in these
flow length grids. Refer to the Terrain
Analysis documentation on flow accumulation grids for more information
and images.
Projection file for Africa
Projection file for Asia
Projection file for Australia
Projection file for Europe
Projection file for North America
Projection file for South America
| Region | Major Basins | Modified Terrain Grid | Flow Direction Grid | Flow Length | Flow Accumulation |
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| Asia |  |
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| Australia |  |
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| Europe |  |
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| North America |  |
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| South America |  |
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| Africa | Asia | Australia | Europe | North America | South America |
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Primary Contact
Kwabena Asante
University of Texas at Austin
Center for Research in Water Resources
Austin, Texas 78712
e-mail: kwabs@mail.utexas.edu
Online: http://www.ce.utexas.edu/stu/asanteko
Phone: (512) 471-0073
Fax: (512) 471-0072
These materials may be used for study, research, and education, but
please credit the authors and the Center for Research in Water Resources,
The University of Texas at Austin. All commercial rights reserved. Copyright
1999 Center for Research in Water Resources.
