Numerical Modeling of a Heavy Rainfall Event in a Future Climate

In a previous study, Lanicci et al. (2017) examined a heavy rainfall event over the Kennedy Space Center (KSC) region of central Florida (8-10 October 2011, the Columbus Day Weekend Storm) using the Weather Research and Forecasting (WRF) model. This heavy rainfall case was characterized by a persistent pattern of sea breeze-related deep moist convection, followed by landfall of a “no-named” hybrid low-pressure system. Three-day regional rainfall totals ranged from 305 to 432 mm (12–17 in.), and produced high winds and flooding throughout the KSC area. The WRF simulation of this case, while challenging due to the formation of the hybrid low in the midst of the study period, was adequate enough to be representative of the present climate, and thus used as a control run for comparison with two different future climate simulations. At the time Lanicci et al. (2017) presented the results of the present climate simulation, preparations were underway to run the case using WRF after altering the initial and boundary conditions based on GCM projections for the October 2090 decade using IPCC (2013) data for representative concentration pathways RCP4.5 (intermediate warming case) and RCP8.5 (strong warming case). The present study describes the results of these future climate simulations.

The average simulated rainfall for RCP4.5 is 10.2 mm (0.4 in.) greater than the current climate simulation, with a maximum grid point difference of 235.7 mm (9.28 in.). Spatial patterns of accumulated rainfall show that RCP4.5 portrays a better-defined north-to-south rainfall maximum inland from the coastline than the current climate simulation, suggesting that RCP4.5 produced a better-defined and stronger sea breeze than the current climate simulation.

The average simulated rainfall for RCP8.5 is lower than RCP4.5, which is counterintuitive given the warmer conditions assumed by RCP8.5 compared to RCP4.5. The spatial rainfall patterns in RCP8.5 suggest that the sea-breeze front did not advance as far inland as it did during RCP4.5 and is less well defined, which may explain the lower rainfall accumulations.

Despite inconsistencies when comparing accumulated rainfall to simulated radar reflectivity, the model runs suggest that future climates may be able to generate high, localized rainfall totals, even though the overall spatial averages may be lower than those in the present-day climate.

References

IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp. doi:10.1017/CBO9781107415324.

Lanicci, J.M., T.D. Allison, and H.E. Fuelberg, 2017: Numerical modeling of a heavy rainfall event in present and future climates. 29th Conference on Climate Variability and Change (American Meteorological Society), 22–26 January 2017, Seattle, WA.