Marvin E. Quesada

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...

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.

Análisis climático de la precipitación anual e interanual en la cuenca media del río Grande de San Ramón, Costa Rica

This project investigates three sectors located in the central basin of the rio Grande San Ramon in Costa Rica. In spite of their proximity to each other, these stations show considerable variation, both temporal and spatial in intra- and interannual precipitation. This variation is attributed to regional atmospheric circulation patterns in the equatorial Pacific, producing strong precipitation during some years, and declines in others. There is a greater probability of lower annual precipitation during El Nino years and higher probabilities of large totals during La Nina years. The warm phase, El Nino, of the El Nino-Southern Oscillation phenomenon (ENSO) is more pronounced in Naranjo, which is located on the lower slope of the Central Volcanic Mountain range. The influence of regional/hemispherical cannot be regarded homogeneous in mountainous areas where local conditions may prevail.