The coastal winds off western subtropical South America in future climate scenarios

Abstract

The west coast of subtropical South America is characterized by a semi-arid climate and very persistent southerly winds that often exhibit a low-level jet structure. The nearly alongshore flow forces coastal and offshore upwelling of cold, nutrient-rich waters, thus supporting one of the most productive marine ecosystems in the world and a wealth of fishery resources. Therefore, the evaluation of the changes in the coastal winds in future climate is a key step to predict the regional environmental impacts of global climate change linked to anthropogenic greenhouse gas (GHG) increases. In this work we document the wind changes between present-day conditions and those projected for the end of the 21st century under two Intergovernmental Panel on Climate Change (IPCC) scenarios (A2 and B2). We first estimate and interpret the changes of the wind field over the southeast Pacific from 15 coupled atmosphere–ocean Global Circulation Models (GCMs). Very consistent among the GCMs is the strengthening of the southerlies along the subtropical coast as a result of a marked increase in surface pressure farther south. We then examine the coastal wind changes in more detail using the Providing REgional Climate for Impact Studies (PRECIS) regional climate model (RCM) with 25 km horizontal resolution nested in the Hadley Centre Atmospheric global Model (HadAM3). PRECIS results indicate that the largest southerly wind increase occurs between 37–41 °S during spring and summer, expanding the upwelling-favourable regime in that region, at the same time that coastal jets at subtropical latitudes will become more frequent and last longer than current events. During fall and winter, the strengthening of the southerlies occurs at subtropical latitudes maintaining a mean jet year-round. Finally, we discuss the possibility that strengthening of the coastal southerlies might actually lead to a relative regional cooling even as the world as a whole continues to warm up. Copyright  2008 Royal Meteorological Society