Trends in Total and Extreme South American Rainfall in 1960–2000 and Links with Sea Surface Temperature

Abstract

A weeklong workshop in Brazil in August 2004 provided the opportunity for 28 scientists from southern South America to examine daily rainfall observations to determine changes in both total and extreme rainfall. Twelve annual indices of daily rainfall were calculated over the period 1960 to 2000, examining changes to both the entire distribution as well as the extremes. Maps of trends in the 12 rainfall indices showed large regions of coherent change, with many stations showing statistically significant changes in some of the indices. The pattern of trends for the extremes was generally the same as that for total annual rainfall, with a change to wetter conditions in Ecuador and northern Peru and the region of southern Brazil, Paraguay, Uruguay, and northern and central Argentina. A decrease was observed in southern Peru and southern Chile, with the latter showing significant decreases in many indices. A canonical correlation analysis between each of the indices and sea surface temperatures (SSTs) revealed two large-scale patterns that have contributed to the observed trends in the rainfall indices. A coupled pattern with ENSO-like SST loadings and rainfall loadings showing similarities with the pattern of the observed trend reveals that the change to a generally more negative Southern Oscillation index (SOI) has had an important effect on regional rainfall trends. A significant decrease in many of the rainfall indices at several stations in southern Chile and Argentina can be explained by a canonical pattern reflecting a weakening of the continental trough leading to a southward shift in storm tracks. This latter signal is a change that has been seen at similar latitudes in other parts of the Southern Hemisphere. A similar analysis was carried out for eastern Brazil using gridded indices calculated from 354 stations from the Global Historical Climatology Network (GHCN) database. The observed trend toward wetter conditions in the southwest and drier conditions in the northeast could again be explained by changes in ENSO.

Widespread Amazon forest tree mortality from a single cross‐basin squall line event

“…Observational evidence for this increase has been reported over a number of tropical areas [IPCC, 2007] including the Amazon region [Khan et al, 2007;Haylock et al, 2006]. If a warming climate increases storm intensity, forest mortality may also increase, resulting in an unexpected carbon release to the atmosphere over many years, with the potential to further warm the climate system.…”

Spatio‐temporal rainfall patterns in Southern South America

“…Stations in the eastern foothills of the Cordillera (Bariloche, Esquel, Balmaceda, Lago Argentino and Punta Arenas) show a marked decrease in rainfall due to the rain shadow (Figure 2). Even lower precipitation amounts are recorded for stations close to the Atlantic coast (Trelew, Rivadavia, Gobernador Gregores and Rio Gallegos) where the rainfall originating from the Pacific Ocean is drastically reduced and the air masses coming from the Atlantic Ocean only contribute very sporadic convective rainfall events (Pittock, 1980;Haylock et al, 2006).…”

Changes in extreme wet events in Southwestern China in 1960–2011

“…For instance, the National Climate Center (1998) reported an economic loss of approximately $36 billion and more than 3000 deaths owing to the severe floods that occurred in the Yangtze River and NenjiangeSonghuajiang valley in China in summer 1998. Lately, temperature and precipitation extremes have been widely discussed in various regions around the world, such as the United States (Vincent et al, 2005;Haylock et al, 2006), Asia (You et al, 2011;Li et al, 2012), and Africa (New et al, 2006;Tramblay et al, 2012). Changes in extreme events exhibit large regional variations because of the different effects of climate changes on geographically diverse regions (Wang et al, 2013a).…”