Interannual variability of annual streamflow and the Southern Oscillation in Costa Rica

Abstract

This study illustrates the association between annual and seasonal streamflow characteristics on six Costa Rican rivers and the Southern Oscillation Index (SOI). Annual discharge from rivers within the Pacific watershed are clearly positively associated with contemporary values of the SOI and experience significant reductions in both mean and variance in El Nine years. The considerable practical implications of this finding to a country in which over 60% of national electrical power comes from hydroelectric schemes is illustrated using quantile estimates from various models. Rivers draining towards the Caribbean show less clear and coherent patterns of associations. The observed associations with seasonal flows on some rivers appear to be the opposite of those on the Pacific, and may even vary during the course of a year at a site. The exact nature of the response seems to be closely related to the elevation of the gauge site. The larger the proportion of the basin at elevations above about 500-1000 m the greater the similarity to the Pacific pattern, suggesting that the marked topographic divide between the two coastal watersheds does not correspond to the divide in associations between streamflow and the SOI.

Hydrological implications of the Southern Oscillation: variability of the rainfall-runoff relationship

“…A recent regional analysis of 18 rivers located throughout New Zealand (Mosley, 2000), highlighted the potential for considerable regional diversity in the individual response of rivers to the ENSO. Similar variability was observed by George et al (1998) for six rivers in Costa Rica, with elevation being observed as a contributing factor governing the association of the ENSO to hydrological response. At the even finer regional-catchment scale little work has been documented.…”

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

“…Figure 1 reveals stations in all regions of Costa Rica, with the exception of the extreme northeast and east central regions, and a strong bias towards the populated Central Valley. Following the definition of the Veranillos and Caniculas in this region (Hastenrath, 1967, , 1950-1999 (lower). 1975; George et al, 1998, andMagaña et al, 1999), July and August rainfalls are summed to create a single seasonal total. For the sake of simplicity and to maximize the size of the available data sets, each set is subdivided into four categories dependent upon the SST anomalies (positive or negative) in the two oceans in the corresponding season.…”

“…A reduction in the drought increases the risk of flooding in the subsequent months of heavy rains. 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).…”

Can climate variability information constrain a hydrological model for an ungauged Costa Rican catchment?

“…Hydrological models can provide such information, but traditional calibration techniques require hydrological data, which often are of low quality and/or not available in many regions worldwide, such as Central America. On the other hand, climate variability exerts a strong influence on streamflow variability on long and short timescales, particularly in the Central American region—where it frequently causes droughts and floods with many negative consequences (Alfaro & Pérez‐Briceño, ; George, Waylen, & Laporte, ). Furthermore, there is a good knowledge about this variability, commonly expressed in terms of variations in precipitation at intra‐annual and interannual timescales.…”