Interdecadal changes in the precipitation seasonal cycle over Southern South America and their relationship with surface temperature

Abstract

The decadal variability in the structure of the annual precipitation cycle over Southern South America (SSA) is analysed with the purpose of investigating whether the lower frequency variability laid bare by annual data is also evident in the annual precipitation structure. Climatic analysis shows that the annual cycle plus the semi-annual cycle dominate the annual variability of precipitation in SSA and represent most of the physical factors responsible for the observed patterns. The percentage of variance explained by the annual cycle shows 2 local maxima, in northwestern Argentina and southern Chile, with opposite phases, summer and winter. The interdecadal analysis of the annual cycle shows 2 areas of relevant variability: one over the central east and the other over the north east. In the first area, there is a positive trend in the variance explained by the first harmonic, indicating that precipitation tends to be better represented by an annual cycle, a fact that might indicate a climatic change in so far as this variable is concerned. In view of global warming, and as a first step towards quantifying the relationship between temperature and precipitation in the region, correlation coefficients are evaluated. The correlation structure of the warmer period 1943-52 generally shows a slight correlation pattern when compared to the 2 colder periods, 1955-64 and 1966-75. In northwestern Argentina, the highest positive correlation coefficients are found at the coldest times in 1955-64, and are probably related to an increase in cloudiness. During summer months (November to February), there is an inverse relationship between precipitation and temperature over most of SSA. That is, warmer/colder summers are associated with precipitation below/above the mean. In autumn and spring months, the correlation is positive in the eastern part of Argentina and Paraguay, and represents well the mechanism of maximum precipitation in this area, which is mainly the result of cyclogenesis. Winter correlation shows a weak positive pattern over SSA and a negative correlation area to the east of the Cordillera de los Andes, which is more intense in spring. KEY WORDS: Precipitation · Seasonal cycle · Decadal · Temperature · Southern South AmericaResale or republication not permitted without written consent of the publisher Clim Res 16: 1-15, 2000 circulation. More recently, Chen & Yen (1997) concluded that interdecadal changes in the southern hemisphere circulation may exhibit different spatial structures during different seasons, with major interdecadal variations occurring in mid and high latitudes. The relevance of interdecadal variation is such that in a paper by Cayan et al. (1998), for example, the authors concluded that decadal variations of precipitation over western North America account for 20 to 50% of the variance in annual precipitation.Concerning the precipitation regime over Argentina and its variability, the first work on seasonal precipitation regimes was Prohaska's (1952) paper. In that study, regions...

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

“…In all indices except CDD, these stations have showed a decrease, which in most cases is significant. These findings are consistent with previously discussed studies noting a rainfall decrease in this region (Minetti 1998;Minetti et al 2003;Rusticucci and Penalba 2000).…”

“…They identified a third region in northern Argentina that had seen a steady increase up until the 1980s when strong El Niño events caused a general decline. Similar trends were observed at some stations in southern South America by Rusticucci and Penalba (2000). They noted that the Chilean station Valdivia (used in this study) had seen a large decrease in total annual precipitation over the period 1901-90, mainly because of a decrease in winter precipitation.…”

Spatio‐temporal rainfall patterns in Southern South America

“…They found a leading mode that explains more than 50% of the variance corresponding to zonal westerlies activity south of 40°S and subtropical anticyclones over the western coast north of 40°S. Rusticucci and Penalba (2000) analysed the interdecadal variability of precipitation using 1901-1990 records from 79 stations in Chile and Argentina. Their interdecadal harmonic analysis found three types of stations: those stations with high seasonality and a strong annual cycle; those where the annual precipitation is uniformly distributed over the year (e.g.…”

Variability and trends of heating degree‐days in Argentina

“…Only a small region in the centre, around 33°S/60°W, seems to be the most important, with significant loadings >0.9. A marked rise in mean temperature has been observed in this region (Rusticucci and Penalba, 2000), clearly represented by the positive trends in seasonal maximum and minimum temperatures (Rusticucci and Barrucand, 2004). The PC loading pattern reveals a major negative trend of −53.9°HDD per decade (see Figure 4(b)) estimated over the average time series.…”