An Introduction

GCTE's operational definition of "global change" encompasses far more than just changes in climate and atmospheric composition. It also includes change in land use, as driven by demographic, economic, technological, and social pressures. Over the next few decades this human dimension of global change will have the most profound influence on the fate of terrestrial ecosystems; one aspect intimately associated with this change in land use (but also linked to the other changes discussed above) is soil erosion and it poses a major threat for sustainable land management.

Soil erosion is a very widespread phenomenon, and is usually irreversible. Once the nutrient-rich surface soil has been lost, the ability to sustain plant growth is severely reduced, and increased runoff from the more impermeable subsoils results in reduced plant-available water. Furthermore, erosion brings various associated "off-site" problems, including reduced water quality from increased sediment loads and poorer air quality due to dust.

It has long been known that both water and wind erosion are commonly accelerated by degrading vegetation cover, presently the main manifestation of global change; given a relatively stable set of conditions many successful strategies have been developed for combating erosion. Global change will, however, bring added problems, as it encompasses more than just change in land-use; change in atmospheric composition and, more particularly, change in climate will further stress many systems. The severity, frequency and extent of erosion will certainly be altered by changes in rainfall amount and intensity, and by changes in wind. Global change will thus amplify many current problems, but as certain soil thresholds are exceeded, potentially new and different problems could arise. It will therefore be crucial to understand the potential impacts of global change on soils to allow the predictive capability necessary to improve their management in the future to be developed. The "GCTE Soil Erosion Network" (one of the key components of the soils research agenda of the Global Change and Terrestrial Ecosystems Core Project of the International Geosphere-Biosphere Programme), is dedicated to this goal.

One of the unique features of GCTE is that it has set an internationally agreed research agenda (the GCTE Operational Plan, see above) to investigate the interactive effects of changes in the global change drivers. To achieve its aims, this research will require collaboration between research teams, between nations and between disciplines. The GCTE Soil Erosion Network is designed to provide the international coordination and linkages necessary to achieve the Network's objectives.

Network Objectives

The GCTE Soil Erosion Network is being developed around three closely interrelated themes:

(i) Erosion monitoring

Since erosion processes commonly only start beyond a certain threshold set of conditions, emphasis will be put on the determination of such thresholds, on reversibility of processes, and on soil resilience. Infrequent climatic events, such as heavy storms, typhoons, etc. can trigger severe erosion, that would be unpredictable from short-term records. Long-term erosion monitoring is therefore essential to observe possible transient and non-equilibrium responses to climatic and land use changes. For inclusion in the Network monitoring studies must

(ii) Experimentation

Despite the numerous current and past soil erosion experiments, many uncertainties about the mechanisms involved remain. Furthermore, as many experiments are very site-specific, extrapolation of results is difficult. These uncertainties must be resolved by detailed experimentation to gain the understanding required to allow models to be developed that are both highly sensitive to global change and sufficiently flexible to be relevant under the largest range of conditions.

Past experiments have often been at the "run-off" plot scale, using land cover and tillage as experimental variables. These variables are of course key determinants of erosion rate, and the Network will build on the valuable base-line data and understanding gained from such experiments. However, GCTE is interested in the interaction of global change driving forces. The Network will therefore also examine the impact of changed variance and mean for key climate parameters and the effects of elevated CO₂, via their direct and indirect impact on aggregation and aggregate stability.

(iii) Modelling

Erosion processes are both varied and complex, and several modelling approaches have been developed for a range of temporal and spatial scales, for erosion by both water and by wind. These, and other, approaches need to be systematically validated across environmental space to determine which are most robust for global change studies. The broad range of data covering the space-time domain flowing from the many monitoring and experimental programmes worldwide will be used to calibrate, initialize and validate soil erosion simulation models; this will be one of the primary objectives of the network.

(These three aspects of the Network are discussed in detail in a series of papers related to the GCTE Soil Erosion Network published in a special issue of the Journal of Soil and Water Conservation, 51, 1996.)

Details about how to join the GCTE Erosion Network are given in Annex III.

The Report lists the metadata (descriptions) of those projects that are formally accepted in the GCTE Soil Erosion Network at the time of printing (further studies are very much welcomed - see Annex III). Its aim is to promote collaboration by publicising and detailing work suitable for global change studies; it allows researchers to identify suitable work for bi- and multi-lateral collaborative studies.

The Report is structured in four sections: Models; Experiments; Monitoring Studies; and Annexes. Models appear in alphabetical order according to model name, and experiments and monitoring studies according to contact name.

For further details about the GCTE Erosion Network, please contact:

Dr Christian Valentin, GCTE Task 3.3.2 Leader
ORSTOM, 32 Rue Henry Varagnat, 93143 Bondy Cedex, FRANCE.
Tel +33 1 48025500
Fax +33 1 48473088
e-mail valentin@orstom.rio.net 

or

John Ingram, GCTE Focus 3 Officer
GCTE Focus 3 Office, NERC Centre for Ecology and Hydrology
Maclean Building, Crowmarsh Gifford, Wallingford, Oxon OX10 8BB, UK
Tel +44 1491 692410
Fax +44 1491 692313
email: jsii@ceh.ac.uk