Warming rates in a large subtropical shallow Brazilian lagoon

Climate change impacts on lake surface water temperature (LSWT) have been mostly investigated in deep northern lakes, and are less understood in southern hemisphere shallow lakes. We evaluated the seasonal warming rates of a large (surface area c.a. 10000 km²) shallow choked lagoon in southern Brazil, with a 22 yr time series of MODIS-derived LSWT, and meteorological data. We found high LSWT warming, with a rate of 0.6°C dec^-1 in spring and of 0.3°C dec^-1 in summer. We also found a high correlation between water and mean air temperature trends, as well as a substantial shortening of the cold season. Spatially, there was some homogeneity in the warming rates but prominent point spatial differences, which may result from the variability of the tributaries’ temperature or discharge or decreased water transparency. The high warming rates found here are comparable to those found in deep northern lakes although the changes and processes of heating differ. The stronger warming in early spring can result in accelerated process rates and an earlier start of the phytoplankton growing season.