Under climate change, future hydroclimate changes could be well outside the extremes of the current historical records. General circulation models (GCMs) predict that tropical precipitation will increase within convective zones, and decrease at the margins of the convective zones. Florida and most of the Caribbean are at the margins, and most GCMs predict that rainfall will decrease over Florida and the Caribbean. This drying signal is more pronounced during the summer (South Florida's rainy season). However, because of the insufficient resolution of the land-sea distribution of current GCMs, it is unclear what their predictions means for the local region of South Florida.

To address this issue, we are applying the Ocean-Land-Atmosphere Model (OLAM) version 4.0r to perform high-resolution simulations in the South Florida/Caribbean region. OLAM, a relatively new Earth System Model partly based on the (older) well-known Regional Atmospheric Modeling System (RAMS), is a numerical simulation / dynamical global model capable of simulating one or more regions of interest at very high resolution while keeping the rest of the world at a coarser resolution. OLAM carries out a consistent, two-way communication between events in the mesoscale and the global portions of the domain through conservative advective and turbulent transport. OLAM uses an unstructured grid with hexagonal cells (plus a few pentagonal and heptagonal cells for mesh refinement) that easily conforms to the globe without a coordinate transformation. The consistent regional-to-global scale communication makes OLAM an ideal tool for investigating the possible impacts that future global climate change may have in our local region.

A decade-long OLAM timeslice simulation for the late Twentieth Century is performed, driven by monthly-averaged prescribed observed sea-surface temperatures (SSTs) and sea-ice extent from the Hadley Centre Sea Ice and Sea Surface Temperature data set 1.1 (HadISST1.1). We use a variable characteristic length scale (CLS) of approximately 3.3 km over southern Florida that gradually coarsens to around 105 km for the rest of the planet. OLAM's summer (May through October) rainfall, across southern Florida, is compared both spatially and temporally against different observational high-spatial-resolution rainfall data sets from both satellite and in-situ rain-gauge measurements. We discuss the strengths and limitations of the model for application to water resource planning in South Florida.