Mapping Salton Sea Water Surface Extent and Its Long-Term Changes with Landsat TM Imagery

As the largest body of water in California, the Salton Sea provides important social, economic, and ecological values to the region. However, the Sea has shrunk substantially over time and water quality has deteriorated considerably, mainly caused by agricultural and industrial pollutants, reduced inflow, and enhanced evaporation. Six functionally different spectral water indexes were selected and evaluated to determine their efficiency in estimating water surfaces during excessive growth of algae and outbreaks of green tide when water quality degraded significantly. The evaluation indicated that among the selected water indexes, the modified normalized difference water index (MNDWI) was most efficient in differentiating open water from surrounding non-water features, and the differentiation was least affected by water quality change. MNDWI was applied to each archived Landsat TM imagery of the Salton Sea area acquired between 1982 and 2012. The extracted water surfaces showed that the Sea experienced significant change over the 31-year period and entered an accelerated drying stage in 2005. The results also revealed the clear seasonal variations of water surface extent, which increases from September to January and decreases afterwards.