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The outline for the SALSA Science Plan was derived from an extensive planning effort and the SALSA Workshop, held in Tucson, Arizona, July 31 - August 4, 1995. The Science Plan is not finished, but a draft of the executive summary has been included on this page.
SALSA Program Science Plan Executive Summary
The water balance of marginal and ecologically fragile semiarid lands is the single influence on the ecosystem most critical for its sustainability. As evidence, many landscapes in the southwest United States and northern Mexico have been permanently altered due to the changes, like groundwater mining or grazing, that civilization has brought upon this region's water cycle. These rapid changes and their consequences have led to a pressing societal need to understand how these alterations of the landscape have occurred in order to better forecast the probable consequences of continuing disturbances, whether natural or human-induced, to this tentative balance. By improved hydrological, meteorological, and ecological understanding of the physical processes involved in semiarid areas, science can hopefully provide pertinent guidance to the people responsible for the sound management of these limited resources.
The SALSA (Semi-Arid Land Surface-Atmosphere) Program has been developed as part of continuing efforts to expand hydrometeorological and ecological research from the USDA-ARS Walnut Gulch Watershed to the larger Upper San Pedro Basin spanning the border from Sonora, Mexico to Arizona, USA. SALSA is conceived as a long-term (+five years) monitoring and modeling effort to address pressing societal concerns related to the effects of climate and human-induced change on semiarid lands' hydrological and ecological resources on a seasonal to interannual time frame.
The Upper San Pedro Basin (~6500 km2) is particularly interesting because of the basin's international location, viable riparian habitat, heterogeneous terrain, and variable climate. First, with the significant land-use differences existing on either side of the border that are easily visible from satellites, it presents an excellent location to investigate the impacts of anthropogenic change in regards to desertification, sustainability and feedbacks into the regional hydrology and climate. Second, there are some additional societal concerns in regard to water supply that exist due to the growth of Ft. Huachuca, USA (and its water use) which are in potential conflict with the first U.S. Riparian National Conservation Area established on the San Pedro. The Nature Conservancy has declared the San Pedro riparian corridor one of the "12 Last Great Places of the Western Hemisphere" in terms of ecological diversity and importance. Additionally, the presence and possible expansion of the enormous copper mining operation at the headwaters of the San Pedro in Cananea, Mexico can be detrimental to the basin's groundwater and surface water quality/quantity and, thus, necessitates investigation. Third, the Basin and Range topography of the area provides steep and rugged topography for investigations into poorly understood mountain processes. Associated with this elevation change, the five separate biomes in the basin provide a diversity of land cover rarely found in such a small basin. Lastly, the watershed experiences significant seasonal to interannual climate variability; much of this variability is due to the influence of the "Mexican" or "Southwest" Monsoon and established linkage to El Niño- Southern Oscillation.
Out of an initial planning period and the SALSA workshop, held in Tucson, Arizona from July 31 to August 4, 1995, came the primary question for the program: What are the consequences of natural and human-induced change on the basin-wide water balance and ecological diversity of the Upper San Pedro River Basin at event, seasonal, interannual, and decadal timescales? Answering this question requires an approach that cuts across disciplines and scales. This approach must be synergistically centered around observations and modeling that will link in situ and remote measuring systems. The achieved goal of the multinational SALSA workshop was to integrate single-disciplinary research ideas into collective proposals that will ultimately help to address key issues of water resources and ecological diversity change in the basin; these proposals form the core research tasks for the SALSA Program.
SALSA's approach will be to determine the USPB's water, CO2, and energy balance in order to answer the primary question. To achieve this goal, the two objectives of the program are: 1) To monitor basin-scale hydrometeorological and ecological changes to effectively capture seasonal and interannual variability; 2) To investigate critical and poorly understood processes in the basin. To take full advantage of the diverse activities of the program, a careful planning effort is also equally important to coordinate the broad assortment of planned data collection and analysis activities.
The process of achieving the first objective will be to build an extensive archive of basin-wide hydro-meteorological and ecological variables. Namely, the plan calls for the capture of: precipitation, solar radiation, remotely-sensed scenes, near-surface meteorological variables, and surface flux stations located in the different biomes and land cover conditions of the basin. Establishing and validating these data collection activities will be a priority. Additionally, a basin-scale hydrological model will serve as the regional integrator of the hydrological variables. We anticipate that these modeling and data collection activities will provide an all-important, long-term data set for improvement in model predictions of seasonal to interannual variability in monsoon strength and timing, though this is beyond the scope of current plans. Achieving these objectives will establish the Upper San Pedro Basin as the North American semiarid site for assessing the impacts of climatic variation and for calibrating and validating algorithms and process-based models developed for NASA/EOS and other orbiting sensors. SALSA envisions the data collection and model improvement tasks of the first objective as US-Mexican contributions to the research programs of the Global Ocean Atmosphere Land System (GOALS) program and the Global Energy Water-cycle Experiment (GEWEX).
The second objective of the SALSA Program involves addressing the key research questions in the basin, which will lead to a more complete regional understanding of basin's energy balance and water resources. The intent of SALSA is to establish a credible research program that will not only produce viable science but also contribute answers helpful to resolving natural resource questions relevant to society. To highlight this important characteristic of the program, the major societal, land and water use issues are used to frame the important, integrative science challenges for the program. The three major societal issues with some of the associated research studies can be classified accordingly:
Societal Issues and Associated Research topics:
1) water resources allocation remote measurements of precipitation, soil-plant-atmosphere interactions, surface water/groundwater/ET interactions, in situ and remote flux measurements, mountain front recharge 2) ecological diversity and habitat changes long-term landscape and habitat change, plant species functioning, regional ecological assessments, land surface characterization using remote sensing 3) climate change and desertification land cover degradation and influences on regional climate, scale issues and derivation of effective surface parameters, remote sensing of surface fluxes over heterogeneous terrain, utilization of remotely sensed data in mesoscale meteorological models Critical information about the hydrological and ecological state of the basin will be provided by addressing these scientific challenges. Fortunately, many of the activities have been established to some extent in the basin, and the multifaceted activities on going in the basin make it attractive for researchers with independent funding to participate. SALSA plans to coordinate these projects and perform key gap-filling research in order to provide information paramount to addressing the societal concerns involved. While these concerns are specific to the Upper San Pedro Basin, they represent in general critical issues faced in semiarid regions around the globe (e.g., Texas, USA, Middle East, North Africa); consequently, many of SALSA's anticipated results will have a wide range of applicability.
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