Precipitation patterns associated with El Niño / Southern Oscillation in Panama

Extensive analysis has been conducted over the past decades which show the impacts of El Niño Southern Oscillation (ENSO) on various regions throughout the world; however, few published works concentrate on detailed impacts of ENSO in the Central American region. The current study focuses on the ENSO impacts of precipitation along the Isthmus of Panama. The resulting analysis will provide knowledge about rainfall variability on seasonal and interannual timescales which will be useful for agricultural and water resources planning and Panama Canal operations. Monthly total precipitation data are provided by Empresa de Transmisión Eléctrica S.A. (ETESA), which includes 32 stations with records from 1960 to 2004. Monthly mean precipitation differences between neutral and extreme (cold or warm) ENSO phases are used to analyse ENSO's impact on the region. Statistical tests are applied to each station to provide confidence levels for the identified changes in precipitation monthly means, as well as any possible shifts on the onsets of the dry and rainy seasons.

Preliminary findings from analysis of four stations in Panama show an increase of precipitation, with respect to the neutral ENSO phase, of 25% to 90% in the second peak of the wet season (Sept-Nov) during cold ENSO phases. The warm ENSO phase shows a decrease of total precipitation at one of the stations located along the western Pacific coast. The cold phase of ENSO tends to dry out the onset of the first rainy season by up to 50%, with respect to the neutral ENSO phase, for two stations along the Pacific coast. The geomorphological composition of Panama may affect the degree of impact of the ENSO phases within the different regions in the country.