MEASURING WATER USE IN A GREEN ECONOMY - UNEP

domains where this kind of information is the
only type available, for example in some areas
of climate science, stratification and ex-post
sampling can provide possible solutions if the
databases are rich enough. However, there is
often a mismatch between the scales used in
modelled data and observations and the data
reported within national statistical systems. To
be of use in water accounting, modelled data,
observations and statistical information all
need to be correctly inter-calibrated.
One way to harmonise data is by using a
standard classification scheme. Examples
of this include the Land Use and Land Cover
nomenclatures in the United Nations System
of Environmental and Economic Accounts and
the draft common international classification
operationalised and sustained global network
of in-situ observation sites and an increased
availability of information products and
services for monitoring changes in the water
cycle (GEO, 2010).
Spatial data derived from earth observations,
such as Gravity Recovery and Climate
Experiment (GRACE) are an additional
source of information for water accounting
(GRACE, 2011). In recent years the resolution
of the sensors and the orbital positioning of
platforms have improved considerably, with
the result that global observations of parts
of the hydrological cycle can be obtained on
a daily basis. The main concern with these
sources is that detecting change is not
straightforward; simple algorithms for image
of ecosystem services, which contains classes
for water resources and flow regulation (EEA,
2010). At the global level the Group of Earth
Observation System of Systems (GEOSS) work
programme has set up tasks with international
high level scientific participation to develop an
processing and change mapping are often
insufficient and can give rise to misleading
results. Despite these challenges, information
from satellite sources is becoming increasingly
important.
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