Flood occurrences in two basins on opposing flanks in Costa Rica

Abstract

The climatic and topographic diversity of Costa Rica provides an ideal opportunity to study the temporal variability of flooding in two basins on opposing flanks within the country. The Candelaria basin drains the Pacific flank and the Sarapiquí drains the Caribbean flank. Each basin displays very different precipitation and flow characteristics. The Candelaria basin experiences lower flood discharges during warm phases of ENSO (El Niño/Southern Oscillation), especially in the period following the "veranillo", a situation which is reversed during cold phases. Meanwhile, no such reduction of flows is noted in the Sarapiquí. However, in warm phase-years, the  robability of floods increases during December, associated with cold fronts originating in North America.  Although the frequency of flood events declines as the defining truncation level increases, the distributions of their magnitudes above that level and their dates of occurrence remain constant. The reduction in frequency and the parameters of the distributions are forecast table, based on the statistical properties of the events above the lower critical level.