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This chapter re-examines El Niño/Southern Oscillation (ENSO) related rainfall anomaly patterns in southern South America over the La Plata basin during the 1912-1999 period. Global associated anomaly patterns of the sea surface temperature and the sea level pressure for this same period are also re-examined. Monthly composites of the variables are obtained for El Niño and La Niña events separately. These composites are also stratified accordingly to the phases of the Pacific decadal oscillation (PDO). The composites show quite robust (weak) and well defined (noisy) spatial structure when the ENSO and the PDO phenomena are in the same (opposite) phase. So, the present analysis provides strong indications that the non-linear aspects of the climate relative to the PDO phases and to the ENSO phases should be taken into account for both climate monitoring and forecasting purposes, in particular for the La Plata basin climate. 183 CHAPTER LOW-FREQUENCY VARIABILITY Mary T. Kayano 1 and Rita V. Andreoli 1 1 Instituto Nacional de Pesquisas Espaciais, São José dos Campos, SP, Brasil. ABSTRACT XIV
Low-frequency variability 14.1. Background on low frequency variability It is well known that the Tropical Pacific is dominated by a single mode of interannual climate variability, which reflects in the ocean-atmosphere coupling expressed by El Niño/Southern Oscillation (ENSO) phenomenon. Interannual climate variations in many parts of the globe are closely related to this mode. However, the Pacific climate contains another mode (or modes) of variability similar to the ENSO, but varying in a decadal to multi-decadal scale. Among these modes a recurring anomalous mode of the ocean-atmosphere system in the Pacific with dominant multi-decadal sign in the North Pacific has been known since the end of the 1980s (Nitta and Yamada 1989; Trenberth 1990; Trenberth and Hurrel 1994; Tanimoto et al. 1993; Latif and Barnett 1994; Mantua et at. 1997; Minobe 1997, 1999; Enfield and Mestas-Nuñez 1999). This mode shows significant climate teleconnections and it is commonly referred to as the Pacific (inter-) Decadal Oscillation (PDO) mode (Mantua et al. 1997; Zhang et al. 1997). The high PDO phase or the warm PDO regime (WPDO) features anomalously cold surface waters in the western and central North Pacific and warmer than normal surface waters in the central and eastern Tropical Pacific and along the West coast of Americas (e.g., Zhang et al. 1997; Mantua et al. 1997; Zhang et al. 1998; Enfield and Mestas-Nuñez 1999). The low PDO phase or the cold PDO regime (CPDO) features nearly reversed patterns. The inter-decadal variability of the ocean-atmosphere system in the North Pacific determines the duration of the PDO regimes, which were cold during the 1900-1924 and 1947-1976 periods and warm during the 1925-1946 period and from 1977 to mid-1990s (Mantua et al. 1997). Mantua et al. (1997) suggested that the PDO constitutes the background of the interannual ENSO variability. In agreement, several authors showed that PDO modulates El Niño (EN) and La Niña (LN) effects in certain regions of the globe (Gershunov and Barnett 1998; McCabe and Dettinger 1999; Gutzler et al. 2002; Krishnan and Sugi 2003). Gershunov and Barnett (1998) found that EN- (LN-) related dry/wet (wet/dry) conditions over the northwestern/southwestern North America tends to be strong and more consistent during the WPDO (CPDO) regime. Since the PDO regimes last about 20-30 years, the information on the ENSO effects stratified accordingly to the PDO phases may have a potential use to improve the climate forecasting. So, this section revises the ENSO-related rainfall anomaly patterns over southern South America, but taking into account the PDO phases. The associated anomaly patterns for the sea surface temperature (SST) and sea level pressure (SLP) will also be obtained and discussed. 184
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CLIMATE CHANGE IN THE LA PLATA BASI
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INDEX FOREWORD . . . . . . . . . .
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7.3. Methodology . . . . . . . . .
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13.3. Regional validation of GCM fo
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1.1. Dropping the hypothesis of sta
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Introduction as they pour water ove
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A better understanding of the obser
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References Introduction Barros, V.
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ABSTRACT The hydrologic cycle of th
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La Plata basin climatology Within t
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in this last description, although
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warm season (October-April), in the
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La Plata basin climatology b. Upper
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La Plata basin climatology 2.3.3. R
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La Plata basin climatology Fig. 2.8
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2.3.7. West and South borders La Pl
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References La Plata basin climatolo
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La Plata basin climatology Robertso
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3.1. Introduction Interannual low f
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Interannual low frequency variabili
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1989). This signal varies along eac
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Interannual low frequency variabili
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The main physiographic and hydrolog
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SUB-BASIN COUNTRY Argentina Bolivia
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the most important stretches of the
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Physiography and Hydrology The Para
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Physiography and Hydrology The Pant
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Physiography and Hydrology forcings
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Physiography and Hydrology It is no
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Physiography and Hydrology tion of
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Physiography and Hydrology INTERNAV
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5.1. Introduction Precipitation and
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From 1956 to 1991, in most of the A
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-15 -20 -25 -30 -35 -40 -15 -20 -25
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Regional precipitation trends 5.3.2
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Regional precipitation trends and L
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trast, other regions suffer floodin
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ABSTRACT The main hydrological tren
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Following are the observed changes:
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In the case of the Paraná River th
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Hydrological trends In order to com
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Hydrological trends In table 6.1 it
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Hydrological trends On the other ha
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the central area of the high basin
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7.1. Introduction Several authors,
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Real evaporation trends a) PET > Pi
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a) b) c) Mean Temperature Real evap
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The positive trends of the mean tem
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d) e) f) Mean Temperature Real evap
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7.5. Discussion and final comments
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ABSTRACT The water, as resource, is
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puts in risk large number of person
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The main services and problems of w
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There are similar problems in diffe
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8.3.3. Energy a. Hydroelectric depe
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(chapters 12 and 13), because of th
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The main services and problems of w
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9.1. Introduction The emissions of
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9.4. Greenhouse effect The atmosphe
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Temperature anomalies (°C) 0.8 0.6
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Global climatic change at a global
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In view of the unavoidability of th
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Background on other regional aspect
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Background on other regional aspect
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Page 141 and 142: ABSTRACT The purpose of this chapte
Page 143 and 144: Global climate models Mid-1970’s
Page 145 and 146: Global climate models Table 11.1. B
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Page 153 and 154: Applicability in impact assessments
Page 155 and 156: of the global climate system to the
Page 157 and 158: Climate scenarios B2: Assumes a wor
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Page 161 and 162: Climate scenarios From Table 12.2 i
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Page 165 and 166: Climate scenarios this would be rel
Page 167 and 168: Results of global circulation model
Page 169 and 170: 13.2.3. Statistical downscaling The
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Page 173 and 174: 10 N EQ 10 S 20 S 30 S 40 S 50 S 10
Page 175 and 176: Regional climatic scenarios Fig. 13
Page 177 and 178: a. Pre-industrial experiment: Initi
Page 183: Regional climatic scenarios Kalnay,
Page 187 and 188: egime occurred during the periods o
Page 189 and 190: Fig. 14.2. As Fig. 14.1, except for
Page 191 and 192: 14.4. SST composites Low-frequency
Page 193 and 194: Low-frequency variability during th
Page 195 and 196: Fig. 14.10. As Fig. 14.9, except fo
Page 197 and 198: Low-frequency variability In genera
Page 199 and 200: Low-frequency variability Mantua, N
Page 201 and 202: 15.1. Introduction Statistical anal
Page 203 and 204: Statistical analysis of extreme eve
Page 217 and 218: CURRÍCULA OF THE AUTHORS Vicente B
Page 219 and 220: Curricula of the autors Rubén Mari
Page 221: Proyect: SGP II 057: “Trends in t
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