1. C. Rodda: On The Problems Of Assessing The World's Water Resources
23
Each of these global centres quality controls the data it acquires before archiving
them and, in addition, as part of the GEMS Water Quality Programme ([36]), a
considerable amount of help is provided to national services to improve and maintain the performance and standards of their analytical services for water quality.
Unfortunately, the data held by these centres only cover some countries. The most
recent are frequently two or three years old and time series are often short.
Lack of a readily accessible and reliable body of hydrological data for the globe
has led WMO to initiate the establishment of a World Hydrological Cycle
Observing System (WHYCOS), which would consist initially of about 1,000
stations located around the world on the major rivers ([37]). Each station would
monitor about 15 variables, including flow and physico-chemical determinants of
water quality, which would be transmitted via one of the geostationary satellites,
such as Meteosat, to national, regional and global centres. These centres would
build up archives of data over the period of operation of WHYCOS (at least 20
years) and process it to create tools for decision making, as well as for science.
These archives would be extensions to existing national archives and to those
compiled for Friend purposes, as well as to the existing global data centres, such as
the Global Runoff Data Centre. WHYCOS would also contribute to the Global
Climate Observing System (GCOS) and to the Global Terrestrial Observing
System (GTOS). More importantly, WHYCOS would seek to build up the
capabilities of the Hydrological Services in those countries where networks, staff
levels and facilities are in decline. This decline has been revealed in a number of
recent studies, a decline which is most marked in Africa ([38], [39]). Because of
this decline, an increase in the errors surrounding water balance estimates is to be
expected. These errors would apply to most scales, basin-wide to global. Indeed,
it is something of an enigma that at the time when global demand for water is
rising faster than ever before, the errors in assessing just how much water is
available for use are generally increasing. There seems to be the expectation that
there will always be enough water in the well or to fill the reservoir.
In research on the water balance of small basins and for the process studies within
them, the instrument systems are normally more advanced and more complete
than for national networks. Toebes and Ouryvaev ([40]) provided an overview of
observational and other practices for representative and experimental basins and
there are many more recent reviews of experience in individual basin studies ([41],
[42], [43]). Large-scale studies of hydrological processes such as FIFE, HAPEXMOBIHY and BOREAS are relatively recent. Essentially, they couple simultaneous
measurements of a number of variables on different scales in intensive field
campaigns, measurements that may have previously been approached through
different disciplines. These studies are described extensively in the literature, such
as by Dozier ([44]) who considers their experimental design using ground-based
measurements, aircraft and satellites.
5
THE MARGIN OF ERROR
Unfortunately for hydrologists, meteorologists and others involved, determining
water resources needs measurements to be made in the natural environment where
conditions are continually changing with time and where human activities now
impose further modifications.
23
Each of these global centres quality controls the data it acquires before archiving
them and, in addition, as part of the GEMS Water Quality Programme ([36]), a
considerable amount of help is provided to national services to improve and maintain the performance and standards of their analytical services for water quality.
Unfortunately, the data held by these centres only cover some countries. The most
recent are frequently two or three years old and time series are often short.
Lack of a readily accessible and reliable body of hydrological data for the globe
has led WMO to initiate the establishment of a World Hydrological Cycle
Observing System (WHYCOS), which would consist initially of about 1,000
stations located around the world on the major rivers ([37]). Each station would
monitor about 15 variables, including flow and physico-chemical determinants of
water quality, which would be transmitted via one of the geostationary satellites,
such as Meteosat, to national, regional and global centres. These centres would
build up archives of data over the period of operation of WHYCOS (at least 20
years) and process it to create tools for decision making, as well as for science.
These archives would be extensions to existing national archives and to those
compiled for Friend purposes, as well as to the existing global data centres, such as
the Global Runoff Data Centre. WHYCOS would also contribute to the Global
Climate Observing System (GCOS) and to the Global Terrestrial Observing
System (GTOS). More importantly, WHYCOS would seek to build up the
capabilities of the Hydrological Services in those countries where networks, staff
levels and facilities are in decline. This decline has been revealed in a number of
recent studies, a decline which is most marked in Africa ([38], [39]). Because of
this decline, an increase in the errors surrounding water balance estimates is to be
expected. These errors would apply to most scales, basin-wide to global. Indeed,
it is something of an enigma that at the time when global demand for water is
rising faster than ever before, the errors in assessing just how much water is
available for use are generally increasing. There seems to be the expectation that
there will always be enough water in the well or to fill the reservoir.
In research on the water balance of small basins and for the process studies within
them, the instrument systems are normally more advanced and more complete
than for national networks. Toebes and Ouryvaev ([40]) provided an overview of
observational and other practices for representative and experimental basins and
there are many more recent reviews of experience in individual basin studies ([41],
[42], [43]). Large-scale studies of hydrological processes such as FIFE, HAPEXMOBIHY and BOREAS are relatively recent. Essentially, they couple simultaneous
measurements of a number of variables on different scales in intensive field
campaigns, measurements that may have previously been approached through
different disciplines. These studies are described extensively in the literature, such
as by Dozier ([44]) who considers their experimental design using ground-based
measurements, aircraft and satellites.
5
THE MARGIN OF ERROR
Unfortunately for hydrologists, meteorologists and others involved, determining
water resources needs measurements to be made in the natural environment where
conditions are continually changing with time and where human activities now
impose further modifications.