SALINITY RESPONSE OF A CLOSED BASIN TO DROUGHT CONDITIONS

Salinity of a playa lake and surrounding area in a closed basin in northern Mexico was analyzed using remote sensing data (Landsat TM/ETM+) to detect areal and reflectivity changes caused by climatic variability, particularly drought, which occurred in the region from 1992 to 2002. The main salts reported for this closed basin were gypsum and anhydrite, while the possibility of halite, glauberite, nahcolite and thenardite was also considered. Four Landsat scenes between 1986 and 2002 were utilized to examine areal extent of salinity and were then related to climate variations with an emphasis on precipitation. After preprocessing the Landsat scenes, several transformations were performed e.g., PCA, ratios, and tasseled cap. The tasseled cap transformation appears to reveal salinity distribution best. These data were rescaled and fused with other Landsat bands, and geology and vegetation maps were used to develop training sets for supervised classification. Particular attention was sought in the selection of training sets for salinity which were delineated in almost coincident locations on each scene. A supervised maximum likelihood classifier was performed on all four Landsat scenes. Results indicate a pronounced correlation between climatic variation, especially precipitation, and areal extent of salinity in the study area.