12. EARTH OBSERVATION DEMANDS FOR IMPROVED WATER
RESOURCES MANAGEMENT
107
undertook efforts to integrate hydrological records to obtain continental and
global scale water balances. Besides databases on hydrology records,
numerical models can provide essential information on water balance terms.
Numerical hydrological models compute water fluxes at a range of space and
time scales and are therefore important tools to quantify water resources and
evaluate water availability. Land surface models coupled with atmospheric
models represent the exchanges of heat and energy between land and
atmosphere at the continental and global scale. Stendel and Arke (1997)
critically examined the output data of several coupled land surface models
against observations of rainfall, evaporation and surface runoff. Their study
represents the state of the art on large scale distributed water flow analysis.
Another example of bringing together valuable historical records is the
ongoing compilation of the IIMI’s World Water and Climate Atlas by Utah
State University (Hargreaves and Jensen, 1997) which is based on rainfall
and temperature data gathered from 56,000 stations world-wide. The
reference evapotranspiration for unstressed grass has been estimated using
the approach proposed by Hargreaves (1994). This methodology is based on
minimum and maximum near surface air temperatures and extraterrestrial
radiation, and gives acceptable (standard error of estimate of
Allen et al., 1995) to accurate results (standard error of estimate
in non-extreme circumstances). Moisture adequacy—indicating the
need for irrigation and drainage—can be derived from this rainfall and
reference evapotranspiration information at 2.5 km grids. Choudhury (1997)
has published a worldwide assessment of reference evapotranspiration based
on the equation of Penman-Monteith (Monteith, 1965) using satellite and
assimilated data for a 24 month period (January 1987 to December 1988).
Because vegetation affects the radiation, energy and water balances, the
presence of vegetation communities and agricultural areas play a major role
in the establishment of water fluxes. Vegetation Indices determined from
NOAA satellites are available with a resolution of 1.1 km (LAC) and
degraded resolution (GAC), and stored in freely available databases such as
‘Pathfinder’ (e.g., Defines et al., 1995). Land cover data sets have also been
compiled, for example under the auspices of the International Geosphere
Biosphere Program (IGBP) in their working group Data and Information
System (DIS) using vegetation measurements of the 1.1 km LAC data
(‘DISCover’, Belward, 1996). Classes such as croplands and
cropland/natural can be derived from DISCover, though irrigated agriculture
does not appear in the legend of this particular database. A similar situation
can be found on the 10 Minutes Pan-European Land Use Database which
recognizes only arable land. The improved European based databases CoORdination of Information oN the Environment (CORINE; Anon, 1992) and
RESOURCES MANAGEMENT
107
undertook efforts to integrate hydrological records to obtain continental and
global scale water balances. Besides databases on hydrology records,
numerical models can provide essential information on water balance terms.
Numerical hydrological models compute water fluxes at a range of space and
time scales and are therefore important tools to quantify water resources and
evaluate water availability. Land surface models coupled with atmospheric
models represent the exchanges of heat and energy between land and
atmosphere at the continental and global scale. Stendel and Arke (1997)
critically examined the output data of several coupled land surface models
against observations of rainfall, evaporation and surface runoff. Their study
represents the state of the art on large scale distributed water flow analysis.
Another example of bringing together valuable historical records is the
ongoing compilation of the IIMI’s World Water and Climate Atlas by Utah
State University (Hargreaves and Jensen, 1997) which is based on rainfall
and temperature data gathered from 56,000 stations world-wide. The
reference evapotranspiration for unstressed grass has been estimated using
the approach proposed by Hargreaves (1994). This methodology is based on
minimum and maximum near surface air temperatures and extraterrestrial
radiation, and gives acceptable (standard error of estimate of
Allen et al., 1995) to accurate results (standard error of estimate
in non-extreme circumstances). Moisture adequacy—indicating the
need for irrigation and drainage—can be derived from this rainfall and
reference evapotranspiration information at 2.5 km grids. Choudhury (1997)
has published a worldwide assessment of reference evapotranspiration based
on the equation of Penman-Monteith (Monteith, 1965) using satellite and
assimilated data for a 24 month period (January 1987 to December 1988).
Because vegetation affects the radiation, energy and water balances, the
presence of vegetation communities and agricultural areas play a major role
in the establishment of water fluxes. Vegetation Indices determined from
NOAA satellites are available with a resolution of 1.1 km (LAC) and
degraded resolution (GAC), and stored in freely available databases such as
‘Pathfinder’ (e.g., Defines et al., 1995). Land cover data sets have also been
compiled, for example under the auspices of the International Geosphere
Biosphere Program (IGBP) in their working group Data and Information
System (DIS) using vegetation measurements of the 1.1 km LAC data
(‘DISCover’, Belward, 1996). Classes such as croplands and
cropland/natural can be derived from DISCover, though irrigated agriculture
does not appear in the legend of this particular database. A similar situation
can be found on the 10 Minutes Pan-European Land Use Database which
recognizes only arable land. The improved European based databases CoORdination of Information oN the Environment (CORINE; Anon, 1992) and