01 July 2019

A comparison of CCSM4 high-resolution and low-resolution predictions for south Florida and southeast United States drought

Resolving Gulf Stream Variability Important for Long-Term Drought Prediction in Southeast US


It is important to have confidence in seasonal climate predictions of precipitation, particularly related to drought, as implications can be far-reaching and costly—this is particularly true for Florida. Precipitation can vary on fine spatial resolutions, and high-resolution coupled models may be needed to correctly represent precipitation variability. We study south Florida and southeast United States drought in Community Climate System version 4 low resolution (LR; 1° atmosphere/ocean) and high-resolution (HR; 0.5°atmosphere/0.1°ocean) predictions for time means ranging from 3 to 36 months.


This study provides further evidence of the importance of resolved mesoscale ocean phenomena in predicting and simulating climate variability. HR predictions are improved due to the increased ocean resolution, particularly due to better representation of Gulf variability, but we also note that the relationship with tropical Pacific SSTA is also closer to observed in the HR predictions. Though the resolution increase does not perfectly capture all of the impacts to either southeast US or south Florida precipitation, it is a step in the right direction, and is a worthwhile venture for regional predictions.


The very high-resolution in the ocean is of interest here given the potential importance of Gulf Stream on south Florida rainfall. Skill of shorter time-mean South Florida predictions (i.e. 3- and 12-months) are not impacted by increased resolution, but skill of 36-month mean south Florida precipitation is somewhat increased in the high resolution predictions. Notably, over the broader southeast United States the high-resolution model has higher skill for the 36-month mean rainfall predictions, associated with an improved relationship with tropical Pacific and Gulf Stream SSTA. Why this improvement in the broader southeast United States does not extend to Florida is an open question, but does suggest that even further resolution refinements may be needed.

Ben Kirtman
University of Miami