| ABSTRACT | Multi-decadal time-series of observational wave data beginning in the late 1970's are relatively rare. The present study refers to the analysis of the 37-year long directional wave time-series recorded between 1979 and 2015 at the CNR-ISMAR (Italian National Research Council - Institute of Marine Sciences) "Acqua Alta" oceanographic research tower, located in the Northern Adriatic Sea, 15 km offshore the Venice lagoon, on 16 m depth. This length allows to exploit the content not only for modelling purposes or short-term statistical analyses, but also for climatological scale considerations. We explore the dataset both as average climate and its variability, and as possible trends that might be suggestive of more general large scale patterns. This investigation is particularly interesting if the climate of the area where the measurements are available is or may be very sensitive to even small variations of the large scale climate. While looking for the detection of long-term trends, the analysis has been performed on a monthly or seasonal basis, in order to make sure that the results are not affected by the characteristic variability of the annual cycle. A clear decrease of the 99th percentile (February and March are two non-significant exceptions) is evident, paralleled by a smaller, but distributed along the annual cycle, increase of the 50th and 75th ones. Considering the two characteristic wind regimes acting on the area, a distributed decrease of the bora significant wave height can be recognized, repeating the trends found for the overall dataset, while less pronounced tendencies can be addressed for the sirocco conditions. The evolution of the significant wave height distributions for the first and last 10 years of the time series clearly confirms a decrease of the maximum values, but also an increase of the average storm intensity with a shift from the lower to the central part of the distribution. The just drawn conclusions represent a new starting point to dig first into the numerical correlation between the evolution in time of the parameter of interest, namely the significant wave height, and the so-called teleconnections and then to derive a physical interpretation of the recognized interdependencies. For this we refer to the recurring and persistent large-scale patterns of pressure and circulation anomalies that span vast geographical areas, representatives of the atmospheric circulation variability, hence weather systems. |