Stochastic Scenarios for 21st Century Rainfall Seasonality, Daily Frequency, and Intensity in South Florida

We demonstrate that a nonhomogeneous hidden Markov model (NHMM) can be useful for simulating future daily rainfall at 19 stations in South Florida. Using upper atmosphere circulation variables that are typically better represented than precipitation in general circulation models (GCMs), a NHMM conditioned on GCM circulation variables is shown to provide credible stochastic simulations of daily precipitation for future conditions. Seasonality changes as well as changes in seasonal extreme precipitation quantiles, total seasonal rainfall, and number of wet days are assessed. The Coupled Model Intercomparison Project phase 5 simulation of the coupled ocean-atmosphere Euro-Mediterranean Center on Climate Change Climate Model CMCC-CMS for 1948-2100 is used for the demonstration. Seasonality changes emerge naturally from the driving variables, and each season is not modeled separately. The future projections for CMCC-CMS indicate that South Florida may have drier conditions for most of the year. The number of wet days reduces, while extreme rainfall frequency increases. These findings are consistent with recent rainfall trends. A modest reduction in total rainfall in the February-May period and a slight increase in the September-October projected rainfall is noted. Changes in the expression of the North Atlantic subtropical high in the CMCC-CMS simulations appear to influence the new seasonality and patterns of rainfall. (C) 2020 American Society of Civil Engineers.