J. C. Rodda: On The Problems Of Assessing The World's Water Resources
21
Now some of these experiments come under the International Geosphere
Biosphere Programme (lGBP) core project on the Biological Aspects of the
Hydrological Cycle ([27]). Others fall within the World Climate Research Programme, Global Energy and Water Cycle Experiment (GEWEX) ([28]), with its
Continental Scale International Project, focusing on the Mississippi Basin ([29]).
The hydrological cycle provides the power to transport the materials in the
different geochemical cycles; consequently measurements of the fluxes in the
water balance globally and basin-wide are essential in determining the budgets of
these different materials. Knowledge of runoff is needed to estimate the
transported loads of sediment ([30]), carbon ([32]) and other determinants ([33]);
Table IV shows estimates of the transport of material in suspension and solution
from the land mass to the world ocean. Precipitation amounts must be known, in
addition to dry deposition, in order to determine the loads being deposited from
the atmosphere ([33]). A summary of the movement of water and material about
the globe has been made by Berner and Berner ([34]).
4
COLLECTING HYDROLOGICAL DATA
Data on the water balance at the global scale, or for the smallest headwater basin,
must be determined from measurements. Traditionally these measurements have
been derived from networks of ground-based instruments, but now data are
available in an increasing amount from weather radars and from satellite imagery.
Unfortunately only a few countries employ these data routinely in assessments of
water resources. This situation is not likely to improve as most future satellites are
not designed with hydrological applications in mind.
Table V provides a summary of the statistics for the global hydrological
instrument network, compiled from statistics on national networks ([35]), which in
some cases, include the networks employed for research purposes, such as
representative basin studies. These instruments and methods of observation are
operated on a routine basis by the world's Hydrological Services who collect,
analyze and apply the data from them. For many parts of the world and for
certain hydrological variables, coverage is poor. For more limited areas, the
networks are dense and most of the hydrological variables are measured, while
much of the data produced appear to have the desirable characteristics of
reliability, continuity and representativeness. However, the contrasts between the
data rich and data poor areas of the world, and particularly the fact that over 70%
of the globe, (namely the oceans), lacks measurements of precipitation and
evaporation, rarely feature in comments on published global water budgets. Error,
accuracy and precision are words that seem to be absent from most of these
discussions. However, they appear more frequently in the reports of small basin
studies. They should be, of course, the concern of those who operate these
instrument networks and manage the data obtained from them on a regular basis.
Agency-wide, national and international programmes aid this effort to assure
quality. Certain initiatives on the international level aim to assist in quality
assurance, as well as in making international data sets more readily available.
There are, for example, the World Glacier Monitoring Service in Zurich, the
Global Runoff Data Centre in Koblenz, the Global Precipitation Climatology
Centre at Offenbach and the Collaborating Centre for Surface and Groundwater
Quality at Burlington.
21
Now some of these experiments come under the International Geosphere
Biosphere Programme (lGBP) core project on the Biological Aspects of the
Hydrological Cycle ([27]). Others fall within the World Climate Research Programme, Global Energy and Water Cycle Experiment (GEWEX) ([28]), with its
Continental Scale International Project, focusing on the Mississippi Basin ([29]).
The hydrological cycle provides the power to transport the materials in the
different geochemical cycles; consequently measurements of the fluxes in the
water balance globally and basin-wide are essential in determining the budgets of
these different materials. Knowledge of runoff is needed to estimate the
transported loads of sediment ([30]), carbon ([32]) and other determinants ([33]);
Table IV shows estimates of the transport of material in suspension and solution
from the land mass to the world ocean. Precipitation amounts must be known, in
addition to dry deposition, in order to determine the loads being deposited from
the atmosphere ([33]). A summary of the movement of water and material about
the globe has been made by Berner and Berner ([34]).
4
COLLECTING HYDROLOGICAL DATA
Data on the water balance at the global scale, or for the smallest headwater basin,
must be determined from measurements. Traditionally these measurements have
been derived from networks of ground-based instruments, but now data are
available in an increasing amount from weather radars and from satellite imagery.
Unfortunately only a few countries employ these data routinely in assessments of
water resources. This situation is not likely to improve as most future satellites are
not designed with hydrological applications in mind.
Table V provides a summary of the statistics for the global hydrological
instrument network, compiled from statistics on national networks ([35]), which in
some cases, include the networks employed for research purposes, such as
representative basin studies. These instruments and methods of observation are
operated on a routine basis by the world's Hydrological Services who collect,
analyze and apply the data from them. For many parts of the world and for
certain hydrological variables, coverage is poor. For more limited areas, the
networks are dense and most of the hydrological variables are measured, while
much of the data produced appear to have the desirable characteristics of
reliability, continuity and representativeness. However, the contrasts between the
data rich and data poor areas of the world, and particularly the fact that over 70%
of the globe, (namely the oceans), lacks measurements of precipitation and
evaporation, rarely feature in comments on published global water budgets. Error,
accuracy and precision are words that seem to be absent from most of these
discussions. However, they appear more frequently in the reports of small basin
studies. They should be, of course, the concern of those who operate these
instrument networks and manage the data obtained from them on a regular basis.
Agency-wide, national and international programmes aid this effort to assure
quality. Certain initiatives on the international level aim to assist in quality
assurance, as well as in making international data sets more readily available.
There are, for example, the World Glacier Monitoring Service in Zurich, the
Global Runoff Data Centre in Koblenz, the Global Precipitation Climatology
Centre at Offenbach and the Collaborating Centre for Surface and Groundwater
Quality at Burlington.