We analyze a body of rainfall data covering 38 years from five meteorological stations in
the Nicoya Peninsula of the Guanacaste Province, Costa Rica. The purpose of the analysis
is to uncover spatial and temporal variability of rainfall in order to support research into
water and sustainability under the FuturAgua project. We use a variety of statistical
analysis and modelling techniques. The analysis uncovers a relatively suppressed spatial
pattern of rainfall. Rainfall totals for periods shorter than two weeks are dominated by
strong stochastic variability, while longer totalizing periods reveal systematic variation.
Monthly totals show the strong double peak, and associated midsummer drought that
has been previously reported. The annual cycle can be efficiently captured by a double
Gaussian model. A simple application of this model to individual years shows large inter-
annual variability, and a strong dependence of the second rainfall peak on the Oceanic Niño
Index (ONI). A Bayesian analysis confirms the appropriateness of the double Gaussian
model, and quantifies the strength of the dependence on ONI. We discuss the implications
of our statistical analyses for research under the FuturAgua project.Science, Faculty ofNon UBCEarth, Ocean and Atmospheric Sciences, Department ofStatistics, Department ofUnreviewedFacult