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Fig. 14.12. As Fig. 14.11, except for CPDO regime. 14.6. Conclusions Low-frequency variability Concerning the estimation of future hydro-meteorological conditions, Robertson et al. (2001) analyzed the decadal fluctuations of the streamflow for the Paraná River at Corrientes during the 1904-1997 period and provided indications that these fluctuations may be partially predictable. They isolated the oscillatory components with periods of 8 years and 17 years and constructed autoregressive predictive models for each component. Their prediction based upon the 8 year and the 17 year oscillatory components, including data up to the austral summer of 1999, suggested increased probability of below-average flows until 2006. Thus, they found a high probability of drought occurrence in the region of the La Plata River basin during the period from 2002 to 2006. However, it is worth noting that their results are based on near-cyclic components (with periods of 8 and 17 years) of the streamflow for the Paraná River and do not take into account the non-linear component of this parameter relative to the PDO phases. So, the present analysis provides another view of the interannual climate variability in the La Plata River basin, which takes into account the non-linear aspects of the climate in the region relative to the PDO phases and to the ENSO phases. Comparisons between ENSO-related anomaly patterns of SSA rainfall, SST and SLP for the WPDO and CPDO regimes show important differences which represent the non-linear components of these composites relative to the PDO phases (for a given ENSO phase) and relative to ENSO phases (for a given PDO phase). 195
Low-frequency variability In general, these patterns show robust (weak) and quite well (noisy) spatial structure for the composites in which the ENSO and the PDO are in the same (opposite) phase for austral summer and autumn seasons. So, the WPDO (CPDO) background modulates the ENSO-effects in SSA rainfall, enhancing EN (LN) and weakening LN (EN), during austral summer and autumn months. The connection of the PDO phases and ENSO-related rainfall anomalies in SSA is similar to the PDO modulations of ENSO signals in the rainfall in the Northwest/southwest United States analyzed by Gershunov and Barnett (1998). The differences of EN-related rainfall composites in SSA between the WPDO and CPDO regimes might be explained comparing the corresponding SST composites. The SST composites for the WPDO (CPDO) regime resemble the SST anomaly pattern associated with EN conditions in the equatorial eastern Pacific and cold (warm) conditions in the subtropical south-central Pacific defined by Barros and Silvestri (2002) and Vera et al. (2004). So, a possible explanation for the differences in EN rainfall composites in SSA for the WPDO and the CPDO phases lies in the circulation anomalies characterizing differences in EN response in the South Pacific as shown by Vera et al. (2004). Another important aspect shown in the present analysis consists of the nonlinear components of the composites relative to the ENSO phases for a given PDO phase. It is worthwhile mentioning that the ENSO-related precipitation anomaly patterns with positive (negative) values in SSA for EN (LN) events documented in previous studies (Walker 1928; Caviedes 1973; Hastenrath and Heller 1977; Kousky et al. 1984; Ropelewski and Halpert 1987, 1989; Aceituno 1988; Kayano et al. 1988; Kiladis and Diaz 1989; Kayano 2003; Grimm 2003) represent in fact the linear component of ENSO-effects in SSA rainfall. In order to take into account the non-linear component of the ENSO-effects in SSA rainfall, EN and LN composites should be considered separately. The sequences of monthly rainfall of the ENSO composites for SSA rainfall in figures 14.1 to 14.4 might provide guidance for future climate monitoring and forecasting purposes for this region. Another aspect that should be also taken into account for these purposes is the phase of the PDO. Concerning to this, several studies have suggested that the PDO shifted back into the cold regime in the late 1990 (Hare and Mantua 2000; Schwing and Moore 2000; Landscheidt 2001). If the PDO is now in a cold regime, EN-related and LN-related composites for the CPDO phase (Figs. 14.2 and 14.4) are more appropriate guides to estimate future hydro-meteorological conditions in SSA, while the cold regime lasts. The authors were partially supported by the Conselho Nacional de Desenvolvimento Científico and Tecnológico of Brazil. Thanks are due to the UK Meteorological Office (UKMO) for the provision of the sea level pressure data used in this paper. Thanks are also due to Dr. Mike Hulme for the provision of the ´gu23wld0098.dat´ (version 1.0) constructed at the Climatic Research Unit, University of East Anglia, Norwich, UK. 196
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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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Considering the non-linear interact
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SST anomalies also have influence o
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ABSTRACT The purpose of this chapte
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Global climate models Mid-1970’s
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Page 185 and 186: Low-frequency variability 14.1. Bac
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Page 189 and 190: Fig. 14.2. As Fig. 14.1, except for
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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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