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INDONESIA Ecuador INDONESIA Ecuador Interannual low frequency variability: Background El Niño conditions La Niña conditions Neutral conditions Convective circulation AMERICA AMERICA ics and extratropics. These changes are basically related to the weakness, intensification and/or displacements of the large-scale atmospheric circulation in the meridional and zonal planes, mainly those linked to the Hadley and Walker circulations (Kidson 1975; Kousky et al. 1984, Souza and Ambrizzi 2002) as well as large-scale Rossby waves that propagate into the extratropics producing, for instance, changes in extratropical storm tracks (Trenberth et al. 1998; Ambrizzi and Magaña 1999). Recent studies have indicated that the extropical response to SST anomalies such as ENSO-related anomalies is less robust and predictable than the tropical response due to the chaotic nature of extratropical circulations such as transient baroclinic waves, fronts, and the SACZ (e.g., Shukla et al. 2000). The Walker circulation is a result of the “see-saw” in surface pressures between the eastern and western hemispheres linking these action centres through an atmospheric circulation in the zonal plan, restricted in the tropical strip, with ascending branch over the western Pacific and descending branch over the eastern Pacific (Bjerknes 1969). On the other hand, the differential heating between tropic-extratropics, results in the formation of a meridional circulation, the Hadley Circulation, with ascending branch over the equatorial areas and sinking over the subtropical latitudes (around 30° of latitude) in both Southern and Northern Hemispheres (Hastenrath 1985). Figure 3.2 shows a schematic view of the Hadley and Walker circulation during ENSO years. For fur- 37 INDONESIA Ecuador 120ºE 80º W 120ºE 120ºE 80º W 80º W Fig. 3.1. 3-D schematic view of the ocean-atmosphere features during (a) El Niño, (b) La Niña; and (c) a normal year. AMERICA
Interannual low frequency variability: Background ther information about the relationship between Hadley and Walker cells and their impact over the South American precipitation patterns during ENSO years see Ambrizzi et al. (2004). South America is one of the continental areas around the world that is directly influenced by the ENSO cycle (Ropelewski and Halpert 1987). Several studies documented the ENSO impacts (mainly the El Niño events) in the South American rainfall (Aceituno, 1988; Kousky et al. 1984; Rao and Hada 1990; Alves and Repelli 1992; Grimm et al. 1998; Uvo et al. 1998; Diaz et al. 1998; Coelho et al. 1998; Souza et al. 1998b; among others). Findings of these works indicate, in general, that the main areas of South America influenced by ENSO are located at the sections West (Peru and Ecuador), North and Northeast (Amazonian and Brazilian Northeast) and South-Southeast (Southern Brazil, Uruguay and Argentina). In analyses focused on southern Brazil and Southern South America (SSA), Grimm et al. (1998, 2000) showed that the impact on rainfall in summer is much weaker than in spring. In terms of surface temperature impacts during ENSO events over the SSA, Barros et al. (2002) found a modest signal in this region, where only during the austral winter prior to the full development of the ENSO event that there were consistent anomalies in the surface temperature field. In most of the subtropical region, these anomalies are positive during El Niño and negative during La Niña events, with a maximum in northern Argentina. They coincide in time and approximately in space with an enhancement (reduction) of the northern component of the flow, and of the warm advection at low levels in El Niño (La Niña) events. 38 Fig. 3.2. Schematic diagrams showing the anomalous regional Walker and Hadley circulation for the (a) El Niño and (b) La Niña canonical impacts. The blue (red) arrows indicate the regional climatological circulation of the Walker (Hadley) cell and the black thick arrows show the anomalous circulation observed in the ENSO composites. [Adapted from Ambrizzi et al, 2004]
Page 1 and 2: CLIMATE CHANGE IN THE LA PLATA BASI
Page 3 and 4: INDEX FOREWORD . . . . . . . . . .
Page 5 and 6: 7.3. Methodology . . . . . . . . .
Page 7 and 8: 13.3. Regional validation of GCM fo
Page 9 and 10: 1.1. Dropping the hypothesis of sta
Page 11 and 12: Introduction as they pour water ove
Page 13 and 14: A better understanding of the obser
Page 15 and 16: References Introduction Barros, V.
Page 17 and 18: ABSTRACT The hydrologic cycle of th
Page 19 and 20: La Plata basin climatology Within t
Page 21 and 22: in this last description, although
Page 23 and 24: warm season (October-April), in the
Page 25 and 26: La Plata basin climatology b. Upper
Page 27 and 28: La Plata basin climatology 2.3.3. R
Page 29 and 30: La Plata basin climatology Fig. 2.8
Page 31 and 32: 2.3.7. West and South borders La Pl
Page 33 and 34: References La Plata basin climatolo
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Page 37: 3.1. Introduction Interannual low f
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Page 45 and 46: The main physiographic and hydrolog
Page 47 and 48: SUB-BASIN COUNTRY Argentina Bolivia
Page 49 and 50: the most important stretches of the
Page 51 and 52: Physiography and Hydrology The Para
Page 53 and 54: Physiography and Hydrology The Pant
Page 55 and 56: Physiography and Hydrology forcings
Page 57 and 58: Physiography and Hydrology It is no
Page 59 and 60: Physiography and Hydrology tion of
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Page 69 and 70: Regional precipitation trends 5.3.2
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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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Global climate models Table 11.1. B
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Global climate models Table 11.2. M
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Although changes in weather and cli
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Socio-economic variables and also s
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Applicability in impact assessments
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of the global climate system to the
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Climate scenarios B2: Assumes a wor
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Climate scenarios The reliability o
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Climate scenarios From Table 12.2 i
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Climate scenarios Fig. 12.5. The mu
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Climate scenarios this would be rel
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Results of global circulation model
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13.2.3. Statistical downscaling The
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La Plata basin are also considerabl
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10 N EQ 10 S 20 S 30 S 40 S 50 S 10
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Regional climatic scenarios Fig. 13
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a. Pre-industrial experiment: Initi
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Regional climatic scenarios Kalnay,
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Low-frequency variability 14.1. Bac
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egime occurred during the periods o
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Fig. 14.2. As Fig. 14.1, except for
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14.4. SST composites Low-frequency
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Low-frequency variability during th
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Fig. 14.10. As Fig. 14.9, except fo
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Low-frequency variability In genera
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Low-frequency variability Mantua, N
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15.1. Introduction Statistical anal
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Statistical analysis of extreme eve
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CURRÍCULA OF THE AUTHORS Vicente B
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Curricula of the autors Rubén Mari
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Proyect: SGP II 057: “Trends in t
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