Flooding and the El Niño-Southern Oscillation phenomenon along the Pacific coast of Costa Rica

Abstract

Abstract:The rivers of western Costa Rica are prone to considerable interannual variability in¯ooding, which in the most severe years can lead to loss of life, property and national infra-structure. Flood generating processes are exclusively rainfall driven, but are complex in both their spatial and temporal distribution due to the variety of oceanic and continental in¯uences which impinge on the region, and to the various natures and timings of their responses to the El NinÄ o-Southern Oscillation (ENSO) phenomenon. Annual¯oods and partial duration series derived from daily discharge records from four basins within the Paci®c watershed are analysed using a series of standard probability distributions and parameters estimated by means of L-moments. The observed temporal and spatial patterns of¯ood events are consistent with the documented meteorological processes and also exhibit marked changes in behaviour between the two extreme phases of the ENSO phenomenon. Particularly noticeable in this regard are; the variable length of the short dry season, the veranillos, which is related to the strength of the northeast trades, and interrupts the rainy season; the number of¯oods in the period immediately following the veranillos, which is positively associated with the number of tropical storms in the Caribbean basin; and the number of cold fronts emanating from North America during the boreal winter.

The effect of Atlantic and Pacific sea surface temperatures on the mid-summer drought of Costa Rica

“…George et al (1998) also indicate a reciprocal relationship to rainfall and flooding within the Caribbean drainage of Costa Rica. Monthly precipitation and flood risks during this period in Costa Rica have been shown to be associated with the El Niño-Southern Oscillation (ENSO) phenomenon (Waylen et al, 1996;Waylen and Laporte, 1999), however that association is not as strong as has been found in many similar tropical regions (Ropelewski and Halpert, 1989). The recent renewed interest in the factors governing the variability of precipitation in Central America and the Caribbean (Enfield and Alfaro, 1999;Magaña et al,1999;and Giannini et al, 2000), has furthered knowledge from earlier publications (Hastenrath, 1975;Ropelewski and Halpert, 1989;Waylen et al, 1996) and suggest that conditions of the tropical North Atlantic and Caribbean basin may be instrumental in modifying the response to ENSO.…”

“…Enfield and Alfaro (1999) also sought links between atmosphere/ocean conditions in the two ocean basins, suggesting that this may be a contributing factor to the unclear association between ENSO and precipitation in the region (Ropelewski and Halpert, 1989). They conclude that the greatest effect of SST c a n be identified in the dates of onset and conclusion of the rainy season in southern Central America (Costa Rica and Panama), a result supported by an analysis of flooding in four rivers along the Pacific slope of Costa Rica (Waylen and Laporte, 1999). However, due to the limited sets of daily precipitation data, and the use of data derived from 2.5∞ grid squares, the results of Enfield and Alfaro (1999) and Giannini et al (2000) lacked a geographic resolution appropriate to the mountainous topography of the area.…”

Regional water balance modelling using flow-duration curves with observational uncertainties

“…This has resulted in many water-related disasters; flooding with severe consequences such as inundations and destruction of important crops, promulgation of landslides, and loss of lives (Waylen and Laporte, 1999); and sustained droughts with severe consequences for hydro-power generation, water supply, irrigation and tourism (George et al, 1998). The characteristics of the complex regional climate have been well studied (e.g.…”

The coincidence of daily rainfall events in Liberia, Costa Rica and tropical cyclones in the Caribbean basin

“…Major flooding events along the Pacific flank have been attributed to the presence of tropical storms in the Atlantic basin (Waylen and Laporte, 1999). Figure 8 shows the magnitude and timing of the single largest daily rainfall total in each calendar year of record.…”

“…It has frequently been implied, with good physical reasoning and clear empirical evidence, that the occurrence of elevated precipitation along the Pacific flank of Costa Rica is associated with tropical storms in the Caribbean basin (Portig, 1967;Hastenrath, 1967;Coen, 1983;Vargas and Trejos, 1994 (hereinafter 'VT94'); Waylen and Laporte, 1999). The storms reverse the prevailing pressure gradient across the isthmus, drawing air from the eastern equatorial Pacific warm pool, which is generally located between 8 and 10°N during the height of the North Atlantic tropical storm season (Alpert, 1945;Neumann et al, 1988;Hastenrath, 1990;Waylen and Laporte, 1999) (Figure 1).…”