The Full Picture

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The observational aspects of water

cycle knowledge and applications

Richard G. Lawford, Director, International GEWEX Project Office

he availability of adequate and safe water is critical to

the economic development of human societies. Surface

waters are also of great importance for both human and

ecosystem health. The global water cycle provides a conceptual

framework that links observations and scientific understand-

ing to those elements of society which need to plan water

supplies for these purposes. The global water cycle consists

of reservoirs (e.g., oceans, atmosphere, land) and fluxes of

moisture moving from one reservoir to another – redistribut-

ing water and replenishing reservoirs. Reservoirs in the global

water cycle are under a number of pressures, most notably the

growth of the world’s population,

the modification of water

systems for expanded development, the growth of megacities,

climate change and land use.

Observations play a central role in the understanding, monitor-

ing and prediction of variability and change in the global water

cycle. Observations and related value-added products, such as

predictions, are needed for developing water management strate-

gies. This article describes the recent history of the coordination

of global-scale water cycle observations in support of better under-

standing and decision making by water managers.

Historical developments in an integrated approach to water

cycle observations

GEWEX

– Many water cycle issues are coordinated within the

scientific framework of the Global Energy and Water Cycle

Experiment (GEWEX). GEWEX was initiated in 1988 under the

World Climate Research Programme (WCRP), in part to utilize

the growing capabilities of Earth observing systems in an effort to

understand the climate system. To a large extent the GEWEX

mission could be defined functionally as the development and

application of planetary Earth science, observations and models

to climate and hydrology. GEWEX has contributed to the devel-

opment of more than 40 coordinated projects and activities that

involve global and regional datasets and products, climate system

analyses, model development, predictability studies, field

campaigns, process studies and applications.

Global observing systems

– In order to plan Earth observation

systems in a more coordinated fashion, several observational

programmes were launched. In the 1990s, the Global Observing

System programmes were established to address the needs of differ-

ent communities to coordinate observational systems. These

included the Global Climate Observing System (GCOS), the

Global Terrestrial Observing System (GTOS) and the Global Ocean

Observing System (GOOS), all of which deal with

elements of the global water cycle. The GCOS plan

deals with many of the issues that concern the water

cycle community.

IGOS-P

– In 1998, the Committee on Earth

Observation Satellites (CEOS) joined with global envi-

ronmental programmes to form the Integrated Global

Observing Strategy Partnership (IGOS-P). IGOS-P

launched a number of themes and established the

necessary working groups to oversee their implemen-

tation. In 2004, the Integrated Global Water Cycle

Observations (IGWCO) theme was approved. IGWCO

has developed a number of strategic initiatives includ-

ing the observation of priority water cycle variables,

the integration of datasets of different types, and the

use of information in meeting the demands of users.

IGWCO strategies act to improve coverage, utility and

integration of critical water cycle observations.

Specific IGWCO activities include:

• Precipitation: in collaboration with GEWEX and the

International Precipitation Working Group (IPWG),

IGWCO has begun to evaluate integrated high-reso-

lution precipitation products

• Soil moisture: soil moisture activities support the

GCOS Implementation Plan and the launch of the

Soil Moisture and Ocean Salinity Mission (SMOS)

by the European Space Agency (ESA)

• Water quality: IGWCO is assessing the potential of

remote sensing to detect areas with poor water quality

• Streamflow: streamflow activities are supporting the

development of an integrated surface water runoff

product building on enhanced in situ observations

and altimetry measurements

• Groundwater: plans for an assessment of the

adequacy of groundwater observations are under

development.

Other IGWCO activities of a more integrative nature

involve collaboration with the Coordinated Enhanced

Observing Period (CEOP)

strengthening links with

GTN-H (Global Terrestrial Networks – Hydrology)

and capacity building efforts taking place in Latin

America and Asia.

GEO

– In 2004, the Group on Earth Observations

(GEO) was initiated to lead in the development of the

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