Climate and freshwater resources in northern Mexico: Sonora, a case study
Magaña VO, Conde C
61: (1) 167-185 MAR 2000

An analysis of current trends in water availability in the Mexican border state of Sonora is presented to illustrate what may be faced under climate change conditions. Precipitation, streamflow and even dam levels data are examined to estimate what changes have been experienced in recent decades. There are indications that the more frequent occurrence of EL Nino/Southern Oscillation (ENSO) events have resulted in more winter precipitation and consequently in a slight increase in water availability in northwestern Mexico. However, water demands grow much faster than such trends in water availability, mainly due to a rapid increase in population in urban areas and in socio-economic activities such as those related to agriculture, industry and power generation. Some strategies to adapt or mitigate climate change conditions are proposed.

Feedbacks between hydrological processes in tropical South America and large-scale
ocean-atmospheric phenomena
Poveda G, Mesa OJ
10: (10) 2690-2702 OCT 1997

The hydroclimatology of tropical South America is strongly coupled to low-frequency large-scale oceanic and atmospheric phenomena occurring over the Pacific and the Atlantic Oceans. In particular, Fl Nino-Southern Oscillation (ENSO) affects climatic and hydrologic conditions on timescales ranging from seasons to decades. With some regional differences in timing and amplitude, tropical South America exhibits negative rainfall and streamflow anomalies in association with the low-warm phase of the Southern Oscillation (El Nino), and positive anomalies with the high-cold phase. Such dependence is illustrated in the hydroclimatology of Colombia through several empirical analyses: correlation, empirical orthogonal functions, principal component, and spectral analysis, and discussion of the major physical mechanisms. Observations show that ENSO's effect on river discharges occurs progressively later for rivers toward the east in Colombia and northern South America. Also, the impacts of La Nina are more pronounced than those of El Nino. Evidence is also presented to show that processes arising from land-atmosphere interactions in tropical South America affect sea surface temperatures in the Caribbean and the north tropical Atlantic. A hypothesis is formulated to explain these feedback mechanisms through perturbations in precipitation, soil moisture, and evapotranspiration over the continent. To begin with, the occurrence of both phases of ENSO affects all those fields. The proposed mechanisms would constitute the ''land-atmosphere'' bridge connecting Pacific and Atlantic SST anomalies.

Seasonality in ENSO-related precipitation, river discharges, soil moisture, and vegetation index
in Colombia
Poveda G, Jaramillo A, Gil MM, Quiceno N, Mantilla RI
37: (8) 2169-2178 AUG 2001

An analysis of hydrologic variability in Colombia shows different seasonal effects associated with El Nino/Southern Oscillation (ENSO) phenomenon. Spectral and cross-correlation analyses are developed between climatic indices of the tropical Pacific Ocean and the annual cycle of Colombia's hydrology: precipitation, river flows, soil moisture, and the Normalized Difference Vegetation Index (NDVI). Our findings indicate stronger anomalies during December-February and weaker during March-May. The effects of ENSO are stronger for streamflow than for precipitation, owing to concomitant effects on soil moisture and evapotranspiration. We studied time variability of 10-day average volumetric soil moisture, collected at the tropical Andes of central Colombia at depths of 20 and 40 cm, in coffee growing areas characterized by shading vegetation ("shaded coffee"), forest, and sunlit coffee.

The annual and interannual variability of soil moisture are highly intertwined for the period 1997-1999, during strong El Nino and La Nina events. Soil moisture exhibited greater negative anomalies during 1997-1998 El Nino, being strongest during the two dry seasons that normally occur in central Colombia. Soil moisture deficits were more drastic at zones covered by sunlit coffee than at those covered by forest and shaded coffee. Soil moisture responds to wetter than normal precipitation conditions during La Nina 1998-1999, reaching maximum levels throughout that period. The probability density function of soil moisture records is highly skewed and exhibits different kinds of multimodality depending upon land cover type.

NDVI exhibits strong negative anomalies throughout the year during El Ninos, in particular during September-November (year 0) and June-August (year 0). The strong negative relation between NDVI and El Nino has enormous implications for carbon, water, and energy budgets over the region, including the tropical Andes and Amazon River basin.

Trends in streamflow and rainfall in tropical South America: Amazonia, eastern Brazil, and
northwestern Peru
Marengo JA, Tomasella J, Uvo CR
103: (D2) 1775-1783 JAN 27 1998

Long hydrological records, from the Amazon Basin, northeastern Brazil, and northwestern Peru spanning most of this century, are examined for trends in rainfall (three wettest months) and runoff (three months of highest flow) or stage, where no rating curves exist. Trends are tested for significance using the Mann-Kendall statistic. In basins where large soil, aquifer, or man-made reservoirs give rise to appreciable over-year storage, flows and water levels may be serially correlated. Where serial correlation exists, the usual statistical tests (linear regression, t-test, and Mann-Kendall) will overestimate the significance of trends, showing significance where none exists. Analysis for trend therefore requires particular care when data are serially correlated, and to avoid misleading results, additional supportive evidence must be sought. For example, rainfall records within the same river basin can be checked for trends; serial correlation in rainfall records, in particular, is less likely to be present, so the validity of any trends in rainfall is less open to question. Strong negative trends were found in flow data from the coast of northern Peru and the Sao Francisco River, while positive significant trends were detected in the Parnaiba River basin. No significant trends were found in the discharge or stage records from Amazonia, while rainfall in northeastern Brazil shows a slow increase over long periods. In the Parnaiba and in some rivers of northern Peru unusually large discharges at the beginning or end of the records seem to account for the direction and significance of trends.

116: (3) 505-524 MAR 1988

246: (4926) 101-103 OCT 6 1989

6: (4) 743-758 APR 1993

This study expands our earlier climate prediction work for Brazil's Nordeste to develop methods of forecasting the March-June precipitation with differing lead times by exploring the potential of various data sources and options of information extraction. Observations include indices of Nordeste rainfall, an index of sea surface temperature (SST) in the equatorial Pacific, and the fields of meridional wind component and SST in the tropical Atlantic. Empirical orthogonal function (EOF) analysis was applied to construct indices of the meridional wind component and SST. These series formed the input to stepwise multiple regression models, an experimental neural network model, as well as to linear discriminant analysis. The dependent dataset 1921-57 (excluding 1943-47) was used for the method development, while the independent dataset 1958-89 was reserved for prediction.

Of primary interest is the prediction of March-June rainfall from information through January. A new SST dataset with improved quality control proved useful, especially with the EOF analysis confined to the more sensitive portion of the tropical Atlantic. The cardinal predictor is, the preseason rainfall. Using indices of the Atlantic meridional wind and SST fields in conjunction with this allows one to predict half to three-fourths of the interannual rainfall variability in the independent dataset. Regarding predictions with greater lead times, about one-fourth of the variance of March-June precipitation can be forecast from the Atlantic SST field in December. Prediction from the February meridional wind and SST fields and preseason rainfall yields no improvement over the forecasts based on information through January. With similar skill, the April-June rainfall is predictable from the end of March. Experiments with neural networking revealed no advantage over regression. Linear discriminant analysis performed best in forecasting extremes.

The essential input information for Nordeste climate prediction consists of accumulated regional rainfall and quality-controlled databases of the Atlantic meridional wind and SST fields, as well as equatorial Pacific SST. For an operational prediction system three phases are found realistic: an early warming from the December SST field; the main forecast of March-June precipitation from rainfall, meridional wind, and SST information by the end of January; and a prediction for the April-June tail of the rainy season based on corresponding information through March. The remarkable recent communal effort in updating datasets was crucial for a real-time forecast of the 1992 Nordeste rainy season.

Variations of sea surface temperature, wind stress, and rainfall over the tropical Atlantic and
South America
Nobre P, Shukla J
9: (10) 2464-2479 OCT 1996

Empirical orthogonal functions (EOFs) and composite analyses are used to investigate the development of sea surface temperature (SST) anomaly patterns over the tropical Atlantic. The evolution of large-scale rainfall anomaly patterns over the equatorial Atlantic and South America are also investigated. The EOF analyses revealed that a pattern of anomalous SST and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical Atlantic. The most important findings of this study are as follows.

Atmospheric circulation anomalies precede the development of basinwide anomalous SST patterns over the tropical Atlantic. Anomalous SST originate off the African coast simultaneously with atmospheric circulation anomalies and expand westward afterward. The time lag between wind stress relaxation (strengthening) and maximum SST warming (cooling) is about two months.

Anomalous atmospheric circulation patterns over northern tropical Atlantic are phase locked to the seasonal cycle. Composite fields of SLP and wind stress over northern tropical Atlantic can be distinguished from random only within a few months preceding the March-May (MAM) season.

Observational evidence is presented to show that the El Nino-Southern Oscillation phenomenon in the Pacific influences atmospheric circulation and SST anomalies over northern tropical Atlantic through atmospheric teleconnection patterns into higher latitudes of the Northern Hemisphere.

The well-known droughts over northeastern Brazil (Nordeste) are a local manifestation of a much larger-scale rainfall anomaly pattern encompassing the whole equatorial Atlantic and Amazon region.

Negative rainfall anomalies to the south of the equator during MAM, which is the rainy season for the Nordeste region, are related to an early withdrawal of the intertropical convergence zone toward the warm SST anomalies over the northern tropical Atlantic. Also, it is shown that precipitation anomalies over southern and northern parts of the Nordeste are out or phase: drought years over the northern Nordeste are commonly preceded by wetter years over the southern Nordeste, and vice versa.

Variability in subtropical Andean Argentinean Atuel river; a wavelet approach
Compagnucci RH, Blanco SA, Figliola MA, Jacovkis PM
11: (3) 251-269 MAY-JUN 2000

A wavelet filter was employed for removing the strong annual wave in the Atuel river runoff data to analyze for other wavelength phenomena of interest and to examine the influence of the ENSO events.
After this removal, the influence of ENSO signal in different frequency bands and indications of climatic changes in bands larger than 10 years could be observed, Other significant phenomena were also observed. As the Andean Argentinean rivers in the Cuyo region have significant similarities, the conclusions about the Atuel river could be extended to other rivers in this region. Copyright (C) 2000 John Wiley & Sons, Ltd.

Inter-annual variability of the Cuyo rivers' streamflow in the Argentinean Andean mountains and
ENSO events
Compagnucci RH, Vargas WM
18: (14) 1593-1609 NOV 30 1998

The main source of the Cuyo rivers' water Volume is the melting of winter accumulated snow over the Andes subtropical high mountains. Particularly between 30 and 40 degrees S, Andean winter precipitation (April-September) shows both spatial coherence and significant correlations with the Santiago precipitation. That is why this zone, which corresponds to the Cuyo rivers' basin areas, is homogeneous with respect to the streamflow's inter-annual variability.

The streamflows of the rivers in this region are highly correlated to each other. Therefore, the Mendoza river, which is one of the Cuyo rivers is taken as reference for all these rivers to study the summer streamflow inter-annual variability (October-March) and the association with ENSO events.

This river exhibits behaviour associated with equatorial Pacific Ocean anomalies. Above average streamflow is more likely to occur during a mature phase of El Nino event in the southern summer. This implies abundant and frequent snowfalls during the previous winter over the high subtropical Andes.
Abundant and frequent snowfalls in the winter after an El Nino year, and the subsequent high flows during the following summer, are less likely to occur. This teleconnectivity is not absolute since some warm events were recorded and simultaneous flows remained below average. Instead, values under the mean flow are more likely during cold event years, with exceptions being quite rare.

This atmospheric circulation study involves principal component analysis of daily surface pressure fields from 1972 to 1983. It reveals identifiable characteristics for Andean winters with above average precipitations. Wet winters are charecterized by both less explained variance by the first principal component, whose pattern corresponds to a high zonal flow component, and more explained Variance of those patterns matching low pressure systems and cold frontal passages which have a high meridional flow component. The inverse occurs in dry winters. Generally, patterns corresponding to post-frontal anticyclones show no significant correlation with the precipitation over the high subtropical Andes. (C) 1998 Royal Meteorological Society.

28: (4) 321-338 DEC 1994

Recent recognition of teleconnections between El Nino and climatic anomalies elsewhere on the planet identify northern lowland South America as a region experiencing drought. Extensive archeological survey along the major tributaries of the Amazon during the past 15 years has defined the temporal and spatial distributions of numerous ceramic phases and traditions. An unexpected result has been identification of discontinuities in most local sequences. Large numbers of carbon-14 dates establish their contemporaneity ca. 1500, 1000, 700, and 400 B.P. These dates correlate closely with archeological evidence on the north coast of Peru for destructive mega-Nino events. Observations of the impact of milder recent episodes on the flora and fauna imply catastrophic deterioration in local subsistence resources during prehistoric events, forcing the repeated human dispersals reflected in the linguistic and genetic heterogeneity of surviving indigenous lowland South American populations.

103: (435) 77-92 1977


Large-scale impoverishment of Amazonian forests by logging and fire
Nepstad DC, Verissimo A, Alencar A, Nobre C, Lima E, Lefebvre P, Schlesinger P, Potter C, Moutinho P,
Mendoza E, Cochrane M, Brooks V
398: (6727) 505-508 APR 8 1999


Amazonian deforestation rates are used to determine human effects on the global carbon cycle(1-3) and to measure Brazil's progress in curbing forest impoverishment(1,4,5). But this widely used measure of tropical land use tells only part of the story. Here we present field surveys of wood mills and forest burning across Brazilian Amazonia which show that logging crews severely damage 10,000 to 15,000 km(2) yr(-1) of forest that are not included in deforestation mapping programmes. Moreover, we find that surface fires burn additional large areas of standing forest, the destruction of which is normally not documented. Forest impoverishment due to such fires may increase dramatically when severe droughts provoke forest leaf-shedding and greater flammability; our regional water-balance model indicates that an estimated 270,000 km(2) of forest became vulnerable to fire in the 1998 dry season. Overall, we find that present estimates of annual deforestation for Brazilian Amazonia capture less than half of the forest area that is impoverished each year, and even less during; years of severe drought. Both logging and fire increase forest vulnerability to future burning(6,7) and release forest carbon stocks to the atmosphere, potentially doubling net carbon emissions from regional land-use during severe El Nino episodes. If this forest impoverishment is to be controlled, then logging activities need to be restricted or replaced with low-impact timber harvest techniques, and more effective strategies to prevent accidental forest fires need to be implemented.

Climate variability in southern South America associated with El Nino and La Nina events
Grimm AM, Barros VR, Doyle ME
13: (1) 35-58 JAN 1 2000

A comprehensive view is given of the precipitation and circulation anomalies associated with the various stages of El Nino (EN) and La Nina (LN) events all over southern South America (SSA). This view comprises the delineation of coherent regions with respect to precipitation anomalies, the identification of the seasons of maximum anomalies, the indication of their magnitude, and the assessment of their consistency during those events. In addition, the spatial and temporal variability of these anomalies is detailed by calculating the expected precipitation percentiles and the consistency of wet and dry anomalies for each station and each three-month running season during EN and LN events. Composites of circulation anomalies and an assessment of their consistency are also presented and their connection with the precipitation anomalies is discussed.

Southern Brazil presents the strongest average signal in EN events. The general behavior toward opposite signals in the precipitation and circulation anomalies over SSA during almost the same periods of the EN and LN events indicates a large degree of linearity in the response to these events. The timing of the anomalies changes throughout SSA, leading to the identification of eight different coherent regions in the EN case and six in the LN case. This regionalization is mostly caused by different processes leading to precipitation anomalies in SSA during those events. All these regions show a significant response in some part of each event.

The magnitude and consistency of this response show a large spatial variability and some areas present very strong and consistent anomalies sometimes not disclosed when large coherent regions are analyzed. In spite of the differences in timing, some features of the precipitation anomalies are rather uniform throughout the region during EN and LN events. In EN episode, there is a tendency to lower than median precipitation in the year before the event, which continues until March of the year of the event. In a Vast region, east of the Andes, the strongest positive precipitation anomalies occur in spring of this year, when the circulation anomalies concur to enhance rainfall over several regions. During the summer of the mature stage the positive precipitation anomalies almost disappear and then reappear in some regions in late summer-early autumn and in winter of the year following the starting year of the event. This description holds partially for the LN event, but with opposite signs, although there is a larger spatial variability in the LN-related anomalies in the following year and some shifts in timing. As for precipitation, the symmetry of the geopotential height anomaly fields with opposite signs between LN and EN cases is also remarkable, especially during the year (0).

Variabilidade interanual de la precipitación: señales del ENSO y del gradiente meridional hemisférico de temperatura.
Barros V, Castañeda ME, Doyle M
Impacto de las Variaciones Climáticas em el Desarrolllo Regional un Análisis Interdisciplinario
VII Congreso Latinoamericano e Ibérico de Meteorologia
321-322, 1996

Estudio de Vulnerabilidad de los Oasis Comprendidos entre 29º y 36º S ante Condiciones más Secas en los
Andes Altos.
Canziani OF, Quintela RM, Prieto
Projecto UNDP ARG/95/G/31, Programa Naciones Unidos para el Desarrollo, Argentina
Cap. 10, 116 pp., 1997

Incidencia del fenómeno El Niño em la Hidroclimatolgía del Valle del río Cauca em Colombia
Carvajal Y, Jiménez H, Materón H., 1999

Anomalias de precipitação do sul do Brasil em eventos de El Niño.
Grimm A, Teleginsky SE, Freitas EED
Congresso Brasileiro de Meteorologia, Anais Sociedade Brasileira de Meteorologia
Brasil, 1996

Impacto del Fenómeno "El Niño" sobre la Producción de Cultivos em la Región Pompeana
Magrin GO, Grondona MO, Travasso MI, Boullón DR, Rodriguez CD, Messina CD
INTA-Boletín de divulgación
16 pp, 1998

Interannual variability of surface climate in the Amazon basin.
Marengo J
International Journal of Climatology
12: 853-863, 1992

Águas atmosféricas.
Silva Dias P, Marengo J
Águas Doces no Brasil-capital Ecológico Usos Múltiplos, Exploração Racional e Conservação
[da Cunha Rebouças, ª, B. Braga Jr., e J.G. Tunizi]. IAE/USP
65-116, 1999

Acerca del fenómeno El Niño sobre la precipitación en la Pampa Húmeda Argentina.
Tanco R, Berri G
Impacto de las Variaciones Climáticas en la Desarrollo Regional un Análisis Interdisciplinario
VII Congreso Latinoamericano e Ibérico de Meteorologia
319-320, 1996

Influence of Sea Surface Temperature on Rainfall and Runoff in Northeastern South America
Uvo C
Analysis and Modelling Diss Department of Water Resources Engineering
Lund University, Lund, Sweden, 120 pp, 1998

Introducción al estudio de las relaciones entre los ciclos de ENSO y la temperatura media en la República Argentina.
Vila DA, Berri G
Impacto de las Variaciones Climáticas en el Desarrollo Regional un Análisis Interdisciplinario.
VII Congreso Latinoamericano e Ibérico de Meteorologia
311-312, 1996

Estudio preliminar sobre las relaciones del ENSO y la frecuencia de días com lluvia en la Pampa Húmeda
Vila DA, Grondona MO
Impacto de las Variaciones Climáticas en el Desarrollo Regional un Análisis Interdisciplinario.
VII Congreso Latinoamericano e Ibérico de Meteorologia
309-310, 1996

Sobre impactos de eventos El Nino e La Niña sobre a precipitação em todo o Brasil na primavera-verão:
Grimm, A. M., 2003: The El Niño impact on the summer monsoon in Brazil:
regional processes versus remote influences. Journal of Climate, 16, 263-280.

Grimm, A. M., 2003: How do La Niña events disturb the summer monsoon system in Brazil?
Publicado por Climate Dynamics on line em dezembro de 2003 e ainda sem referência na versão impressa.

Sobre impactos de eventos El Nino e La Niña sobre a temperatura no Cone Sul da América do Sul:
Barros, V. R., A. M. Grimm, e M. E. Doyle, 2002: Relationship between temperature and circulation in
Southeastern South America and its influence from El Niño and La Niña events.
Journal of the Meteorological Society of Japan, 80, 21-32.

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