homepageSALSA 1995 Workshop Summary
A "Meeting Report" on the SALSA workshop held in Tucson, Arizona, August 1995. by Jim Wallace, Institute of Hydrology, Wallingford, UK from Eos, Transactions,
American Geophysical Union, November 14, 1995.
Multidisciplinary Program Studies Land-Atmosphere Interactions in Semi-Arid Regions
What are the consequences of climatic and human-induced change on the water-balance and ecological diversity of the Upper San Pedro River Basin (USPB), which spans the border between southeastern Arizona and northern Sonora, Mexico? What are the effects of such change at event, seasonal, interannual, and decadal time scales? The interdisciplinary Semi-Arid Land Surface Atmosphere Program (SALSA) seeks an answer to these complex questions.
Though its research is concentrated in the USPB, SALSA will foster understanding of the ecological, hydrological, and meteorological processes that operate in many semi-arid regions of the world. The program will use ground, aircraft, and satellite equipment to study the processes that control the exchange of heat, water vapor, and CO2 between the land and atmosphere. It also will study the effects of mountain topography on hydrological and meteorological processes; investigate the coupling of groundwater, surface water, and vegetation processes in riparian areas; and derive data from satellites for incorporation in hydrological, meteorological and ecological models of the region.
Sixty-five scientists from nine federal agencies, eight universities, six foreign agencies, one private organization and several NASA/EOS interdisciplinary science , data, and instrument teams met to discuss plans for SALSA in Tucson, Ariz., from July 31 to August 4, 1995. You may not have heard of SALSA yet, but if consensus among the meeting attendees is any indicator, it should soon be as well known as other large scale experiments such as FIFE, the First International Satellite Land Surface Climatology Project Field Experiment, and HAPEX-Sahel, the Hydrological Atmospheric Pilot Experiment.
The USPB study area is a unique outdoor laboratory containing diverse vegetation, climatic conditions, and topography, in addition to cross-border land uses that result in clearly visible differences in satellite imagery (Figure 1). The upper basin encompasses an area of ~6500 km2 near Benson, Ariz. The head waters are near Cananea, Sonora, in Mexico. Elevations range from 1100 to 2900 m. The annual rainfall ranges from around 300 mm to 750 mm. Topography, climate, and vegetation vary across the region. Biomes including desert scrubland, grasslands, oak savannah, and pinyon-juniper are contained within the USPB, and a ponderosa pine forest lies atop the mountains. In portions of the basin all of these biomes are contained within a 20 km span that is roughly equivalent to a north-south translocation of 2,800 km at a constant elevation!
Establishing the USPB as a key long-term semi-arid site for process-based model validation and pre- and post-launch satellite instrument calibration and testing will provide a key terrestrial data set for programs such as the NASA Earth Observing System (EOS). The area has been well studied in the past. Over several decades, hydrological and meteorological observations have been collected in and around the site via long-term intensively monitored watersheds and through intensive multi-disciplinary field campaigns.
Another important feature of the USPB is the narrow riparian corridor (50-300 m wide) along the river, which contains a high concentration of lush vegetation and large trees that are sustained by the groundwater aquifer. Riparian systems in semi-arid areas play an important role in sustaining exceptional ecological diversity, but they are easily threatened by human activity such as groundwater pumping. The Nature Conservancy has declared the San Pedro riparian corridor one of the "12 Great Places of the Western Hemisphere" for ecological diversity, and it is the first U.S. Congressionally designated Riparian National Conservation Area.
Program planning for SALSA at the workshop was as structured, exciting, and dynamic as the science. Prior to the workshop, the organizers went to great lengths to obtain and collate individual proposal summaries from a range of potential participants. These were arranged in five discipline-oriented groups--ecology/vegetation/soils, meteorology, surface fluxes, surface/groundwater, and remote sensing--and circulated to all participants at the workshop. As a result, only brief overviews of the proposed work needed to be presented, and the meeting was able to quickly move on to the main task of integrating these discipline-oriented groups.
First, each discipline group met to discuss the SALSA program from the perspective of its conventional viewpoint and, specifically, to prepare lists of its products and needs. The entire group then convened to hear the summaries of these deliberations and, based on these, a number of cross-disciplinary groups were formed. This is where the really interesting dynamics took place; landscape ecologists talked to hydrologists; meteorologists talked to soil conservation and land managers; and remote sensors talked to everybody! Most of the scientists discussed their ideas and aspirations with scientists from other disciplines. The switch from discipline-oriented discussion to cross-discipline discussion was further reinforced by appointing cross-group reporters to identify and collate the challenges that lay ahead. Key gaps in the experimental program were exposed, but many were soon filled by collaborative groups who elected to tackle the missing science. The real success of this meeting was in this gap-filling integrative science. Many collaborative ideas were born, and enthusiastic participants left the workshop with resolve to approach their funding sources for backing.
Above all, the workshop was interesting, stimulating, and surprisingly enjoyable. The SALSA program has struck a balance. It is firmly in touch with land management and water resource issues in semi-arid lands while successfully integrating relevant ecology/hydrology/meteorology and remote sensing science. SALSA may not provide solutions to all of the natural resource management problems of semi-arid regions, but the drive, skill, and determination of the scientists involved give it the potential to be one of the best large-scale land surface atmosphere programs ever conducted. The program still requires further development in key areas, and anyone who is interested in contributing should contact David Goodrich (USDA-ARS-SWRC, 2000 E. Allen Rd., Tucson, AZ 85719; E-mail: goodrich@tucson.ars.ag.gov).
Acknowledgments: The workshop was organized by the U.S. Department of Agriculture's Agricultural Research Service and The University of Arizona, Department of Hydrology and Water Resources. Support for the SALSA workshop and publication of this article by the USDA-ARS and the NASA/EOS grant NAGW2425 is gratefully acknowledged. The satellite image in Figure 1 was provided by the Office of Arid Land Studies, The University of Arizona. I thank Hoshin Gupta, David Goodrich, Russell Scott, and Corrie Thies for their help in preparing this article.
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