A procedure for estimating wind waves and storm-surge climate scenarios in a regional basin: the Adriatic Sea case

This study attempts to estimate the effect Of CO2 doubling on the frequency and intensity of high wind waves and storm-surge events in the Adriatic Sea. The meteorological forcings were derived from two 30-yr-long time-slice experiments that simulated the global atmospheric circulation in the present and the doubled-CO2 climate scenarios. These time-slice experiments were carried out by the Danish Meteorological Institute using the ECHAM-4 model at T106 resolution. Unfortunately, the resolution of the T106 wind is inadequate for simulation of the wave field and the storm surge in the Adriatic Sea, and it results in a gross underevaluation of extreme events. In this study, regional surface wind fields have been derived from T106 sea-level-pressure fields by statistical downscaling. Downscaled wind fields have been used to force a wave and an ocean model during the two 30-yr-long simulations. The downscaled wind fields produce a large improvement with respect to the T106 fields, but a systematic underestimation with respect to the observed wave height and surge levels remains present. This shortcoming of the analysis might prevent identification of very intense events. Consequently, extreme-value analysis of the results of the present climate simulation produces values lower than observed, and obviously the same systematic bias is expected in the evaluation of the future climate. Some caution is therefore necessary in the interpretation of the results of this study. Nonetheless, the comparison between the present and future climate simulations shows no substantial change in the extreme surge level and a decrease in the extreme wave height.