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The Program
Regions classified as semiarid or arid constitute roughly one-third of the total global land cover. Within these regions, the dynamic water balance is the single most critical factor in the sustainability of the ecosystems and human populations. As evidence, many landscapes in the southwest United States and northern Mexico have been permanently altered from activities that have changed the water cycle such as groundwater mining and overgrazing. These activities and their consequences have led to a pressing societal need to understand how the alterations of the landscape have occurred in order to better forecast the probable consequences of continuing disturbances, whether natural or human-induced, to this tenuous balance established between an ecosystem's health and the state of the water cycle. From improved understanding of the hydrological, meteorological, and ecological processes involved in semiarid areas, science can hopefully provide pertinent guidance to the people responsible for the sound management of these limited resources.
SALSA constitutes a long-term monitoring and modeling effort to address pressing societal concerns related to the effects of climate- and human-induced change on the hydrological and ecological resources of semiarid regions on a seasonal to interannual time frame. The primary question that SALSA is trying to answer is:
What are the consequences of natural and human induced change on the water balance and ecological diversity of semiarid basins at event, seasonal, interannual, and decadal timescales?Though its research is concentrated in the Upper San Pedro River Basin (USPB), SALSA will foster understanding of the ecological, hydrological, and meteorological processes that operate in many semiarid regions of the world. The program will utilize in-situ and remote sensing observations coupled with models to study the processes that control the exchange of heat, water vapor and CO2 between the land and atmosphere. It will also study the effects of mountainous 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 into hydrological, meteorological and ecological models of the region. Through these activities, SALSA intends to establish the USPB as the North American semiarid validation site for process-based models and products derived from remote sensing.
The Background
The USPB (~6500 km2), spanning the border between southeastern Arizona, USA and northern Sonora, Mexico, encompasses a variety of factors which make it an exceptional outdoor laboratory to address a number of scientific and socio-economic challenges. First, because significant land-use differences exist on either side of the border that are easily visible from satellites, the USPB 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 critical societal concerns in regard to water supply that exist due to rapid urbanization on the U.S. side (and its associated 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 an enormous copper mining operation at the headwaters of the San Pedro may be detrimental to the basin's groundwater and surface water quality/quantity. Third, the Basin and Range topography of the area provides steep and rugged topography for investigations into poorly understood mountain processes. Associated with the topographic gradient, five separate biomes in the basin provide a diversity of land cover rarely found in such a small basin. Fourth, the watershed experiences significant seasonal to interannual climate variability; much of this variability is due to the influence of the Mexican monsoon and established linkage to El Niño- Southern Oscillation. These coupled water resource and ecosystem health issues define the backdrop for the research agenda SALSA strives to complete.
The Philosophy
Addressing the primary question of SALSA 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. One of the achievements of the multinational SALSA workshop, held in Tucson, Arizona, July 31- August 4, 1995, was to integrate individual 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 (see the workshop summary on the homepage for more details).
The SALSA program builds upon a large foundation of ongoing data collection in the basin supported by significant resources from seven federal, two state and two local agencies (U.S.). This data collection has been established to address critical water issues as designated by the San Pedro Technical Review Committee. Approximately $500,000 per annum is invested in water related data collection in the San Pedro. In addition, intensive, long term (30+ years) hydrologic data collection is maintained at the USDA-Agricultural Research Service's Walnut Gulch Experimental Watershed, a sub-basin of the USPB.
Other factors relevant to the SALSA Program include the basin's selection by the NASA Earth Observing Systems (EOS) ASTER instrument team as an arid validation site and its selection as the primary focus site for the EOS interdisciplinary science hydrology team at the University of Arizona and CESBIO, France. Two Sonoran state agencies have been involved in research in the USPB: Centro Ecológico de Sonora and CIDESON. The French organization, ORSTOM, has committed five scientists to work in the Mexican portion of the basin for three years. Six proposals have also been funded for research as well as for remotely sensed data acquisition in the basin which range from ERS-2, SPOT4, ADEOS, and a mesoscale meteorological modeling initiative. Finally, Walnut Gulch/San Pedro has been selected as a Global Land Cover Test Site and is targeted for PRIRODA data acquisition from a Russian satellite. (For more information please see the summaries of funded projects on the homepage).The Objectives
The program strives to become a model for effective international, inter-agency, and university cooperation. 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, and 2) to investigate critical and poorly understood processes in the basin. Moreover, taking full advantage of the diverse activities of the program requires a careful planning and design effort to coordinate the broad assortment of data collection and analysis activities.
To achieve the first objective, an extensive archive of basin-wide hydro-meteorological and ecological variables will be developed. Namely, the plan calls for archiving: 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 over a five to ten year period. Establishing and validating these data collection activities will be a priority. Additionally, a basin-scale hydrologic model will serve as the regional integrator of the hydrological variables. It is anticipated that these modeling and data collection activities will provide an all-important, long-term data set for improved model predictions of the impacts of seasonal to interannual variability on a basin's hydrology and ecology. 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 and Mexican contributions to the research programs of the Global Ocean Atmosphere Land System (GOALS) program and the Global Energy and 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 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 scientific insight 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 scientific challenges for the program. Each major societal issue along with some of the associated research studies can be classified accordingly:
Societal Issues Research topics Water resources allocation: development and improvement, of relevant ground/surface water monitoring and models Remote measurements of precipitation, soil-plant, atmosphere interactions, surface water/groundwater/ET interactions, in-situ and remote flux measurements, mountain front recharge Ecological diversity and habitat changes: land surface characterization as a means to assessing changes in the basin's ecological diversity and landscape Long-term landscape and habitat change, plant species functioning, regional ecological assessments, land surface characterization using remote sensing Climate change and desertification: development and improvement of scientific understanding of how the basin's hydrology and ecology interact with the regional climate. Land cover degradation and influences on local 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 The Participants
SALSA is a multinational effort, comprised of scientists and land managers from a host of U.S. and Mexican federal and state agencies, as well as numerous universities. Additionally, a number of institutions from Europe are involved. For a current list of these participants, please see the homepage.
Call for New Members
There are many outstanding opportunities for new member participation. Your participation is welcome! In particular, new participants are needed to address key research on the understanding of economic policy as it relates to environmental change and conservation. Because SALSA is conceived as an integrated research program, it is encouraged that research ideas be developed to involve researchers from different disciplines coming together to work on understanding key hydrological, meteorological, ecological, and socio-economic issues in the basin. Thus, using the mantra of the August, 1995 workshop SALSA insists that you integrate your ideas with those that have already been proposed by other SALSA participants. The idea is that if you build your ideas with others, existing SALSA folks will attempt, if possible within resource constraints, to make adjustments in their procedures/methods/data collection to optimize benefits to both or multiple groups. The goal is to achieve true integration of data collection, modeling and analysis activities via thoughtful research design and cooperation. If measurements and modeling resources beyond those currently obtainable are required, the SALSA Program can serve as a foundation to develop proposals by leveraging the substantial on-going efforts.
For more information, please visit the SALSA Internet homepage, or contact SALSA organizers David Goodrich or Bruce Goff, 2000 East Allen Road, Tucson, Arizona 85719. Phone 520/670-6481. Internet: goodrich@tucson.ars.ag.gov, bgoff@tucson.ars.ag.gov.
Please send us a proposal that indicates your interest and contact those SALSA members whom you feel you can work with. This will start the process of your inclusion in the SALSA Program.
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