The Full Picture

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Development of a global

in situ soil moisture network

Peter J. van Oevelen, International GEWEX Project Office; Thomas J. Jackson, USDA

Hydrology and Remote Sensing Lab; Pedro Viterbo, Instituto de Meteorologia;

Dara Entekhabi, MIT; Yann Kerr, CNES/CESBIO

oil moisture observations are critical for understanding the

global water and energy cycles. Availability of better spatial

estimates of surface soil moisture will help, through assim-

ilation into hydrometeorological models for example, to improve

forecasting of precipitation, droughts and floods. It will also

contribute to further the development of other hydrological

applications that can support water resource decision-makers.

Surface soil moisture is a determinant of the partitioning of surface

precipitation into infiltration and runoff. Across many landscapes of

the mid and higher latitudes soil moisture and its freeze/thaw state

control evapotranspiration providing the link between terrestrial

water, energy, and carbon cycles. Based on theory and experiments

to date there is a general agreement that improvements in our under-

standing of the water cycle and our ability to predict short-term

events (hydrometeorology) and long-term patterns (seasonal) are

dependent on developing an integrated global soil moisture observ-

ing system. Improving these global observations is needed on a

priority basis.

The Global Energy and Water Cycle Experiment (GEWEX) of the

World Climate Research Programmeme (WCRP) along with the

Integrated Global Water Cycle Observations (IGWCO) theme of

IGOS-P are contributing, amongst others, to the devel-

opment of a global in-situ soil moisture network. Such

a network is intended to support a global soil moisture

observing system as part of the Global Earth Observation

System of Systems envisaged by GEO. The practical

coordination and implementation is done through the

International Soil Moisture Working Group with addi-

tional financial support from the European Space

Agency (ESA) to develop a soil moisture data hosting

centre by the Instituto de Meteorologia in Portugal.

The upcoming launch in 2008 of the Soil Moisture

and Ocean Salinity Mission by ESA has given a strong

impetus to the establishment of the in situ soil moisture

network. The global network will help in validating and

calibration of the SMOS data products. Also existing

sensors such as ASCAT on METOP or AMSR-E can

profit from the established network.

However, the network will not only serve as a satellite

validation tool, as the in-situ soil moisture data has value

by itself in other applications, such as in irrigation prac-

tices. The community perspective on soil moisture

observations parallels that described in Leese et al.

This

included in situ measurements, satellite observations,

and modelling that must all be developed and integrated,

primarily through a data assimilation framework.

Modelling and data assimilation are already integral

components of national and international weather and

climate forecast programmes.

To reach the goal of an integrated global soil moisture

observing system it will be necessary to establish,

expand and improve current soil moisture observations

both in situ and remotely sensed. For the in situ part

this involves global network establishment, enhance-

ment by expansion and standardization, improved

coordination of soil moisture data network planning,

observing standards, and data exchange.

The establishment of a soil moisture data hosting

centre to act as a focal point is crucial in reaching many

of the objectives. Key to the growth of these efforts is

the recognition by international organizations and agen-

cies that soil moisture is an important climate variable

and that committed support is needed. Ultimately we

hope to find a sponsoring agency that will commit to

Photo: Tom Jackson & Gary Schaeffer

Installation of SCAN station in Arizona

OCIETAL

ENEFIT

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