Abstract:
On February 15, 1941, a storm caused one of the major natural disasters in the Iberian
Peninsula in the past century. The storm made landfall in the north of Portugal, leading to a
large surge in the Tagus estuary. Adverse meteorological conditions combined with a high
spring tide led to extensive flooding of dry land, causing severe damage and casualties. A suite
of regional and local scale models is developed to analyze the event and the relative
contributions of the different forcing agents to the extreme water levels. Quantitative and
qualitative validations show that the models adequately reproduce this type of events. The
models are then used to assess the inundation in the upstream reaches of the estuary where
extensive agricultural lands are protected by dikes. Results show that over 25 km2 could be
inundated today, a value that would increase threefold for a sea level rise of 0.5 m. Then, the
relative importance of the different forcing mechanisms on the extreme water levels is
investigated through numerical experiments. It is shown that the regional surge and the setup
induced by swell are the two main drivers of the inundation. In particular, the modulation of the
wave setup by tides induces a semi-diurnal signal which is amplified by resonance inside the
estuary.
