César N. Caviedes

Interannual variability of monthly precipitation in Costa Rica

Abstract The varied monthly precipitation data of stations across Costa Rica are assigned to one of five regions, each of which displays a distinct precipitation regime. Peaks and troughs in each regional regime reflect the relative contribution and timing of the major precipitation-bearing winds flowing from the Pacific, the Caribbean, and continental North America. Lag cross-correlations with a Southern Oscillation index reveal different regional associations, and at differing times, with fluctuating atmosphere-ocean conditions in the tropical Pacific. Patterns of correlations are coherent within each region, but display interregional differences that are more marked than previously suggested. The Pacific coast experiences drought shortly before and during the onset of an ENSO event. The Caribbean coast receives increased summer precipitation but decreased winter rains during these episodes. The interior regions of the country display a mixed response to these events. In the years following a warm phase...

Annual and seasonal fluctuations of precipitation and streamflow in the Aconcagua River basin, Chile

Abstract The El Nino-Southern Oscillation (ENSO) phenomenon has been shown to influence dramatically precipitation and streamflow in tropical western South America. The statistical properties of annual and winter precipitation totals and streamflow characteristics in the Aconcagua River basin, in temperate central Chile, are investigated in such a way as to permit the identification of flood- and drought-generating processes and their possible linkages to upset behavior in the tropical Pacific. Despite the considerable distance to those regions generally associated with ENSO events, the phenomenon produces marked effects upon the various physical processes which govern the surface hydrometeorology of the study area. El Nino years result in significant increases in annual and winter precipitation, particularly along the coastal margin. The likelihood of rain or rain-on-snow flooding, in the succeeding winter, increases, as does the size of spring snowmelt in the southern summer, 1 year after the upset conditions in the tropical region. Annual low flows are of higher magnitude and occur earlier in the year than is usual.

El Niño and annual floods on the north Peruvian littoral

Abstract A three-component mixed Gumbel distribution satisfactorily models the observed annual flood frequencies of rivers in northern Peru which display highly variable annual peak-flood characteristics corresponding to three sets of ocean-atmosphere conditions. Physical support for the “a priori” subdivision of the series is provided by consideration of the regional offshore oceanic-atmospheric conditions. Exceptionally warm waters (El Nino) cause extensive heavy rains; unusually cold waters (anti-El Nino) restrict both the quantity and distribution of precipitation. Model parameters reveal marked spatial trends in the severity and extent of flooding during any set of offshore conditions and geographic shifts in the regional flood-frequency characteristics between such conditions.

TEMPORAL AND SPATIAL VARIABILITY OF ANNUAL PRECIPITATION IN COSTA RICA AND THE SOUTHERN OSCILLATION

Annual precipitation totals from over 100 stations in Costa Rica are analysed to provide estimates of the nature of their response to El Niiio-Southern Oscillation (ENSO) events. Responses are found to be varied in terms of their signs (droughts or excessive precipitation), magnitudes, and durations. The results of simple interstation correlations and lag cross-correlations with the Southern Oscillation Index suggest a marked difference in response in those areas draining towards the Pacific and those towards the Caribbean, as well as latitudinal variations, particularly along the Pacific coast. The marked regional differences in statistical properties over so small an area are related to complex physical processes of precipitation generation, the differing provenances of the humidity laden winds, and the fluctuations of local atmosphere-ocean interactions in response to ENSO.

Rainfall variation, snowline depression and vegetational shifts in Chile during the Pleistocene

Palynological, geomorphological, and relict vegetation evidence point to the existence of cooler and more humid conditions along semiarid and temperate Chile during the Pleistocene. Departing from an actualistic model, and utilizing a regression technique that includes significant independent variables on the basis of R2 and F statistics, the best fit multivariable model was produced for annual rainfall and snowline elevation. Predicted values for rainfall are obtained by controlling sea surface temperatures and air temperatures (the most significant variables in the model) at different latitudes. A variation of only 1 °C of the winter sea and air temperatures induces more than a doubling of the annual precipitation in north-central Chile, and increases by nearly fifty percent in southern Chile. Entering the predicted values of precipitation and lowering the winter temperatures by 1 or 2 °C produces a slight depression of the snowline in semiarid north-central Chile and a significant descent in southern Chile. The predicted depression of the snowline coincided well with geomorphological evidence of glacial advances and fossil periglacial phenomena in the Andes. Cooling and increased precipitation during the Pleistocene pluvial elicited northward shifts of the temperate rainforest of southern Chile in the order of 7 deg latitude.

Natural hazards in South America: In search of a method and a theory

Traditional natural hazard researchers have failed to deal with hazard occurrences in Latin America in a comprehensive and coherent fashion because of their cultural bias and lack of knowledge about the regional implications of hazard conditions.The attempt is made in this paper to point out that some of the climatic hazards that beset South America, such as El Nino phenomenon on the coasts of Peru and Chile, the frosts in south-central Brazil, and the droughts of NE Brazil, are not isolated occurrences, but meteorological anomalies whose implications encompass not only the affected areas but also distant environments and economies.Systems analysis is utilized to prove that the oceanic-climatic El Nino phenomenon is genetically linked to global climatic anomalies and that the effects of such anomalies are felt in the ecological balance of the Pacific basin, of Africa, and of S Asia. Among their economic implications are shortages of anomal protein (from fish meal) and crop failures in Africa and the Soviet Union. Political consequences of hazardous conditions are also evident at hand of the 1971–73 climatic oscillations, of which El Nino was a symptom.In order to provide natural hazard research with a coherent theory, the cusp catastrophe theory of Thom and Zeeman is applied to the understanding of the conditions that lead to the onset of an oceanic-climatic El Nino occurrence. It is suggested that — considering that such a situation arises from interdependent ocean-atmosphere feedbacks — only under very special circumstances does this interplay lead to the sudden development of an El Nino condition. Catastrophe theory is not a deterministic theory but it considers the possibility of sudden change of states within a system.

Anomalous westerly winds during El Niño events: the discovery and colonization of Easter Island

Abstract Using six-hour wind data from Easter Island recorded during the years 1982–1984 it is shown that the usual easterly winds that dominate in the southeastern Pacific in normal years are replaced by westerly winds in the winter and spring preceding a major El Nino event. It is proposed that the observation of these changes by such keen navigators as the Polynesians are known to have been, prompted them to organize maritime expeditions that could have taken them to eastern outposts of Polynesia in a period of four to five weeks. Vector simulation experiments conducted with westerly winds of the years 1979 and 1982 suggest that colonization groups departing from the Marquesas Islands could have come close to Easter Island within that time span.

Natural resource exploitation in Latin America espoiliation or tool for development

The exploitation of natural resources in Latin American countries has become one of the most controversial issues of contemporary development. Three positions arise: 1) a position that opens the development of natural resources to foreign priorities and capitals; 2) a position that opposes any kind of development if it is not conducted by the state, even if the state lacks the financial resources to do so; and 3) a position that sees advantages in negotiating the development of resources with external partnership but reserves for the state the determination of priorities and the leading role in the exploitation. The third position assumes the existence of a responsible government commited to safeguarding national interests. Unfortunately, this last assumption is not very operative with Latin American governments which seldom have standing policies concerning natural resources, which leaves them open to assaults from private national and international interests.Contrary to opposite views, it has been demonstrated that the development of natural resources brings about stimulation of regional economies and relocation of populations toward resource frontiers. Opposing the development of such areas of resources is to negate the concept of progress and to deepen chronic poverty.