Sea Surface Temperature Trends in Venice Lagoon and the Adjacent Waters

Two coastal lagoons and coastal waters in the northern Adriatic region, Italy, were examined to assess the anthropogenic impact on coastal sea surface temperature (SST). The first lagoon was the highly altered Venice lagoon, and the second was the largely natural Marano-Grado lagoon. There are converging lines of evidence for air warming in the Venice region since 1910 at a long-term rate of 0.095 degrees C/decade. Since 1980, the warming has accelerated to 0.65 degrees C/decade in the centre of Venice. The acceleration in air warming is also evident in the MOHAT4 data set from the northern Adriatic Sea, although the rate of warming is less (0.36 degrees C/decade). This warming trend is mimicked in the HadISST1.1 data set of SST for the northern Adriatic Sea (0.33 degrees C/decade), whereas no trend was detected before 1980. SST and air temperature in both Venice and Marano-Grado lagoons are highly correlated (r(2) = 0.8): SST is on average 2 degrees C cooler than the northern Adriatic Sea is, although differences appear to be diminishing because of rapid warming in Venice lagoon since 2008 (up to 1.75 degrees C/decade). The warming in the lagoons appears to be greatest during winter months. By contrast, the greatest (post-1980) warming in the northern Adriatic Sea occurs during summer months. Moderate Resolution Imaging Spectroradiometer (nighttime; MODIS) SST data shows that, on average, the Venice lagoon is 5% warmer than Marano-Grado lagoon is. This equates to a summertime mean temperature difference of 1.2 degrees C. This difference is within the scatter of the data and suggests that there is no appreciable heat retention in the waters of the Venice lagoon because of local anthropogenic activity.