The Chesapeake Bay is one of the largest and most productive estuaries in the world, supporting both an important fishery and recreational opportunities. Since 1975, urban land cover has increased by more than 100% in portions of the Piedmont and Coastal Plain adjacent to the Bay, which has influenced a variety of physical, chemical, and biological aspects of water quality. Over the same period, global climate change has included an increase in air temperature of over 0.5 C, with expected impacts to water temperature in the Bay.
A total of 196 images from Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) that covered the northern two-thirds of the Bay and all of the Bay in Maryland were acquired from the United States Geological Survey (USGS). Using the 10um thermal infrared channel, we corrected for atmospheric effects and generated WST maps from each image. These maps were organized by day of year to generate a WST climatology (a function describing the annual trajectory of WST including minimum and maximum temperatures) at 5-year increments between 1985 and 2012. The mean WST calculated from each climatology was evaluated over time and against air temperature measured at weather stations surrounding the Bay.
To validate the Landsat-based WST observations and the quality of our atmospheric correction, we compiled concurrently-collected in situ water temperature observations from the Patuxent River near Solomons, MD.
Trends of increasing water surface temperature were observed for more than 92% of the Bay. Our results exhibit broad scale patterns in WST, such as water surface climatological differences between the main stem of the Bay and its tributaries. The trend in water temperature increase was weakest at the top of the Bay near its confluence with the Susquehanna River. The trend of increasing water temperature over time strengthened towards the main stem of the Bay, where there is a greater influence of oceanic water. The spatial patterns also show locally more rapid water temperature warming in the Patapsco, Patuxent, and Potomac River estuaries, suggesting that these western tributaries are overall warming faster than the eastern tributaries and portions of the main stem of the Bay. The results also suggest the influence of urbanization and industrialization, such as increases in watershed impervious surfaces and thermal effluent from power plants.