Preface paper to the Semi-Arid Land-Surface-Atmosphere (SALSA) Program special issue

The Semi-Arid Land-Surface-Atmosphere Program (SALSA) is a multi-agency, mu lti-national research effort that seeks to evaluate the consequences of nat ural and human-induced environmental change in semi-arid regions. The ultim ate goal of SALSA is to advance scientific understanding of the semi-arid p ortion of the hydrosphere-biosphere interface in order to provide reliable information for environmental decision making. SALSA approaches this goal t hrough a program of long-term, integrated observations, process research, m odeling, assessment, and information management that is sustained by cooper ation among scientists and information users. In this preface to the SALSA special issue, general program background information and the critical natu re of semi-arid regions is presented. A brief description of the Upper San Pedro River Basin, the initial location for focused SALSA research follows. Several overarching research objectives under which much of the interdisci plinary research contained in the special issue was undertaken are discusse d. Principal methods, primary research sites and data collection used by nu merous investigators during 1997-1999 are then presented. Scientists from a bout 20 US, five European (four French and one Dutch), and three Mexican ag encies and institutions have collaborated closely to make the research lead ing to this special issue a reality. The SALSA Program has served as a mode l of interagency cooperation by breaking new ground in the approach to larg e scale interdisciplinary science with relatively limited resources. Publis hed by Elsevier Science B.V.