ARE WIND WAVE HEIGHTS INCREASING IN SOUTH-EASTERN SOUTH AMERICAN CONTINENTAL SHELF BETWEEN 30°S AND 40°S?

DRAGANI, W. C.; MARTIN, P.B.; SIMIONATO, C. G.; CAMPOS, M.I.

CONTINENTAL SHELF RESEARCH

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2010 vol. 30 p. 481 - 490

0278-4343

A possible increase in wind wave heights in the South-eastern South American Continental Shelf between 30°S and 40° is investigated in this paper. Time series of in situ (1996–2006) and Topex/Poseidon (1993–2001) annual mean significant wave heights gathered at the continental shelf and adjacent ocean presented an apparent positive trend but they were not statistically different to zero. Nevertheless, it must be remarked that analyzed in situ and satellite data constitute a relatively short data series and, particularly, in situ data presents several gaps. There are enough evidences about a possible change in the low atmospheric circulation in this region of the Southern Hemisphere. Consequently, a weak increase in wave height could be occurring which would be hard to quantify due to the shortness and insufficient available data series. In order to study a possible trend in mean annual wind wave heights SWAN model forced with NCEP/NCAR surface wind (1971-2005 period) was implemented in a regional domain. Simulated annual mean wave heights showed significant trend at selected locations of the Buenos Aires inner continental shelf and the adjacent ocean. The most significant increase was obtained between 1991-2000 and 1981-1990 decades. The highest difference (0.34 m, 17%) was detected around 34°S-48°W. This increase in wave height is somewhat lower (13%) on the continental shelf and approximately 10-12% in the Río de la Plata estuary. The annual mean energy per unit sea surface area (spatially integrated in the whole computational domain) also presented a significant positive trend (102 m2/yr) and a relatively high inter-annual variability. The possible link between such inter-annual variability and El Niño and the Southern Oscillation (ENSO) was investigated but no apparent relationship was obtained. The possible increase in the annual mean energy raises two important points to be considered in the region. Firstly, if a possible change in the wind pattern has been able to increase the mean wave height in the region, it is natural to think that an increase in the mean depth of the mixed layer of the ocean could have occurred as well. Secondly, an increment in the wave density energy would be able to produce changes in the littoral processes and, consequently, in the erosion of the coast. In this sense, an increase of the erosive processes along the sandy coast of Buenos Aires province during the last thirty years has been previously reported. Finally, it is remarked that these hypothetic changes are only supported by numerical simulations carried out with SWAN model forced with NCEP/NCAR winds, highlighting the difficulty in separating some possible inhomogeneities in the NCEP/NCAR reanalysis from real climate change.