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African Water Stress Study for the World Water Development Report II
Entry ID: UNH_WWRDII_AFRICA


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Summary
Abstract: Outputs from a Water Balance and Transport Model (WBM/WTM) were used
to determine the spatial distribution of renewable water supply,
expressed as the sum of local runoff and river corridor
discharge. Monthly atmospheric forcings from 1960-95 were from (New et
al., 1998). Estimates of domestic and industrial water demands
(Vorosmarty et al., 2000a; 2004) were apportioned by urban/rural
population densities. Agricultural withdrawals were based on African
water statistics (Jippe Hoogeveen, FAO/AGL, Rome Italy) at the
sub-basin level, and a mapping of irrigation-equipped lands (Siebert
et al., 2002). All supply and demand estimates were resampled as
required and georegistered to a 6 min grid and river network (STN-06),
updated from a previous flow topology (Vorosmarty et al., 2000b) using
a network rescaling algorithm that processed 1-km digital streamlines
(Fekete et al., 2001). STN-06 basin boundaries were compared to a
hand-corrected database provided by FAO. Water scarcity was evaluated,
in part, by computing the Climatic Moisture Index (CMI, Willmott and
Feddema, 1992), the ratio of annual precipitation (P) to annual
potential evapotranspiration, (PET). Specifically CMI = (P / PET) -1
when P < PET and CMI = 1 - (PET/P) when P = PET. The CMI ranges from
-1 to +1 , with wet climates showing positive values, dry climates
negative. PET was estimated using a physically based function
(Shuttleworth and Wallace, 1985). We grouped CMI into major climate
categories following Koppen. The coefficient of variation (CV)
computed for all variables is the ratio of the standard deviation to
the mean over the time series analyzed.

Water supply in each grid cell (n) has two sources: locally-generated
discharge (QLn) and river corridor discharge (QCn), which enters from
upstream cells. QLn is the product of runoff (Rn) and cell area
(An). QCn accumulates QLn in a downstream direction along the STN-06
digital nertwork. Cells with mean upstream runoff < 3 mm yr-1 were
considered inactive or non-perennially discharging (Vorosmarty et
al., 2000b). Water use is represented by local demand (DIAn), the sum
of domestic, industrial and agricultural water withdrawals. Dividing
DIAn by QCn yields an index of local relative water use. A high degree
of stress is indicated when the relative water use index is > 0.4 or
40% (34). DIAn summed in a downstream direction (in a similar manner
as QCn) and divided by QCn is called the water reuse index and
represents the extent to which runoff is recycled or reused as it
accumulates and flows toward the basin mouth. The water reuse index
typically increases in a downstream direction, indicating reuse and
recycling of river corridor water. This index can, however, decrease
when mainstream flow is diluted by more pristine (less-recycled)
tributary waters.

Downloadable files include:
- Agricultural area in km2: Spatial distribution of agricultural area
per grid cell (in km2 per grid cell): FAO/AGL, Rome Italy.

- Annual CMI, mean: Mean annual climate moisture index computed from
1960-1995 annual time series: Willmott and Feddema, 1992.

- Annual CMI, coefficient of variabiltiy (CV): Interannual variability
of the CMI, as represented by the CV, which is computed as the
standard deviation divided by the mean: Willmott and Feddema, 1992.

- Domestic + industrial + agricultural water use, 1995 (DIA, in km3/yr):
Sum of human water use in 1995 in km3/yr per grid cell: Vorosmarty et
al., 2005.

- Annual discharge (Q), mean in km3/yr. Long-term average annual river
flow (discharge, Q) computed from the 1960-1995 time series:
Vorosmarty et al., 2005.

- Annual discharge (Q), 30-yr low in km3/yr.Minimum annual river flow
(discharge, Q) selected from the 1960-1995 time series: Vorosmarty et
al., 2005.

- Annual discharge (Q), annual coefficient of variability
(CV). Interannual variability of discharge, as represented by the CV,
which is computed as the standard deviation divided by the mean:
Vorosmarty et al., 2005.

- Seasonal variability, ratio of monthly maximum to monthly minimum (Q
maxmin): Ratio of monthly maximum discharge to monthly minimum
discharge, representing the range of intra-annual discharge
variability: Vorosmarty et al., 2005.

- Irrigated area: Spatial distribution of irrigation-equipped area (in
km2 per grid cell), aggregated to 6-min (latitude by longitude)
resolution. Primary source: Siebert et al., 2002.

- Annual runoff, mean: Mean annual runoff (in mm/yr per grid cell)
computed from 1960-1995 annual time series: Vorosmarty et al., 2005.

- Annual runoff, coefficient of variability: Interannual variability of
runoff, as represented by the CV, which is computed as the standard
deviation divided by the mean: Vorosmarty et al., 2005.

- Relative water stress index (RWSI), mean annual Q: Ratio of domestic +
industrial + agricultural water use in 1995 (DIA) to long-term mean
annual discharge (Q). Water stress is indicated when RWSI is greater
than or equal to 0.4: Vorosmarty et al., 2005.

- Relative water stress index (RWSI), 30-yr low Q: Ratio of domestic +
industrial + agricultural water use in 1995 (DIA) to 30 year low
discharge (Q): Vorosmarty et al., 2005.

- Months with RWSI exceeding 0.4. Number of months within an average
years during which the RWSI equals or exceeds 0.4: Vorosmarty et al.,
2005.

- Number of people exposed to water stress: Number of people (per grid
cell) within grid cells that experience RWSI equal to or greater than
0.4, on an average annual basis: Vorosmarty et al., 2005.

- Number of people exposed to water stress: Number of people (per grid
cell) within grid cells that experience RWSI equal to or greater than
0.4, for the 30 year minimum discharge: Vorosmarty et al., 2005.

- Water reuse index (WRI), mean annual. Water reuse index is computed as
the ratio of cumulative DIA to mean annual discharge, representing the
degree to which river water is reused by humans as it flows along a
river network: Vorosmarty et al., 2005.

Related URL
Link: GET DATA
Description: Access to African water stress study data


Link: VIEW RELATED INFORMATION
Description: Access to documentation


Geographic Coverage
 N: 40.0 S: -35.0  E: 60.0  W: -10.0

Data Set Citation
Dataset Originator/Creator: Water Systems Analysis Group
Dataset Title: African Water Stress Study
Dataset Series Name: World Water Development Report II
Dataset Release Place: Durham, NH
Dataset Publisher: University of New Hampshire
Online Resource: http://wwdrii.sr.unh.edu/download.html


Temporal Coverage
Start Date: 1960-01-01
Stop Date: 1995-12-31


Location Keywords
CONTINENT > AFRICA


Data Resolution
Latitude Resolution: 6 min
Longitude Resolution: 6 min


Science Keywords
ATMOSPHERE >ATMOSPHERIC WATER VAPOR >EVAPOTRANSPIRATION >POTENTIAL EVAPOTRANSPIRATION    [Definition]
BIOSPHERE >TERRESTRIAL ECOSYSTEMS >AGRICULTURAL LANDS    [Definition]
HUMAN DIMENSIONS >HABITAT CONVERSION/FRAGMENTATION >IRRIGATION    [Definition]
HUMAN DIMENSIONS >ENVIRONMENTAL GOVERNANCE/MANAGEMENT >WATER MANAGEMENT    [Definition]
TERRESTRIAL HYDROSPHERE >SURFACE WATER >DISCHARGE/FLOW    [Definition]
TERRESTRIAL HYDROSPHERE >SURFACE WATER >RIVERS/STREAMS    [Definition]
TERRESTRIAL HYDROSPHERE >SURFACE WATER >RUNOFF    [Definition]
LAND SURFACE >LAND USE/LAND COVER >LAND COVER    [Definition]
HUMAN DIMENSIONS >SOCIAL BEHAVIOR >VULNERABILITY LEVELS/INDEX    [Definition]


ISO Topic Category
FARMING
ENVIRONMENT
IMAGERY/BASE MAPS/EARTH COVER
INLAND WATERS


Project
WWAP >World Water Assessment Programme    [Information]


Keywords
water use
water re-use
water stress
relative water stress index (RWSI)
climate moisture index (CMI)
agricultural water use
industrial water use
domestic water use
potential evapotranspiration
PET
World Water Asessment Programme
World Water Development Report II


Data Set Progress
COMPLETE


Originating Center
UNH


Data Center
Water Systems Analysis Group, Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire    [Information]
Data Center URL: http://www.wsag.unh.edu/

Data Center Personnel
Name: CHARLES J. VOROSMARTY
Phone: (603) 862-1792
Fax: (603) 862-0188
Email: charles.vorosmarty at unh.edu
Contact Address:
Water Systems Analysis Group
Complex Systems Research Center
Institute for the Study of Earth, Oceans, and Space
University of New Hampshire
Morse Hall, 39 College Road
City: DURHAM
Province or State: NH
Postal Code: 03824
Country: USA



Distribution
Distribution_Media: online
Distribution_Format: JPEG, ascii, ARC
Fees: none


Personnel
CHARLES J. VOROSMARTY
Role: INVESTIGATOR
Phone: (603) 862-1792
Fax: (603) 862-0188
Email: charles.vorosmarty at unh.edu
Contact Address:
Water Systems Analysis Group
Complex Systems Research Center
Institute for the Study of Earth, Oceans, and Space
University of New Hampshire
Morse Hall, 39 College Road
City: DURHAM
Province or State: NH
Postal Code: 03824
Country: USA


Publications/References
Fekete, B.M., Vorosmarty, C.J. and Lammers, R.B. 2001. Scaling gridded
river networks for macroscale hydrology: Development, analysis, and
control of error. Water Resources Research 37:7 1955-1967.

New, M., Hulme, M. and Jones, P. 1998. Representing twentieth century
space-time climate variability. Part II: Development of 1901-1996
monthly grids. J. Climate 13: 2217-2238.

Shuttleworth, W.J. and Wallace, J.S. 1985. Evaporation from sparse
crops: an energy combination theory, Quarterly
J. R. Meteorol. Soc. 111: 839-855.

Siebert S., DC6ll, P. and Hoogeveen, J. 2002. Global map of irrigated
areas version 2.1 Center for Environmental Systems Research,
University of Kassel, Germany / Food and Agriculture Organization of
the United Nations, Rome, Italy.

Willmott, C.J., and Feddema, J.J. 1992. A more rational climatic
moisture index. Prof. Geographer 44: 84-87.

Vorosmarty, C. J., E.M. Douglas, P. A. Green and C. Revenga,
Geospatial indicators of emerging water stress: an application in
Africa, Ambio, in press, 2005.

Vorosmarty, C.J., Brunner, J., Revenga, C., Fekete, B., Green, P.,
Kura, Y. and Thompson, K. 2004. Case studies: Population and
climate. In: Kabat, P., Claussen, M., Dirmeyer, P.A., Gash, J.H.C.,
Bravo de Guenni, L., Meybeck, M., Pielke Sr., R.A., Vorosmarty, C.J.,
Hutjes, R.W.A. and Lutkemeier, S. (eds), Vegetation, Water, Humans and
the Climate. Springer, Heidelberg, Germany.

Vorosmarty, C.J., Green, P., Salisbury, J. and Lammers,
R. 2000a. Global water resources: Vulnerability from climate change
and population growth. Science 289, 284-288.

Vorosmarty, C.J., Fekete, B.M., Meybeck, M., Lammers, R. 2000b. A
simulated topological network representing the global system of rivers
at 30-minute spatial resolution (STN-30). Global Biogeochemical Cycles
14, 599-621.

Creation and Review Dates
DIF Creation Date: 2005-12-12
Last DIF Revision Date: 2012-11-02


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