Semester of Graduation

Summer 2021

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

While many of the destructive environmental conditions associated with tropical cyclones are well recognized, tropical cyclone-induced defoliation, a reduction in green leaves and mature vegetation, has been largely overlooked as a source of environmental stress following tropical cyclone passage. The land surface change associated with defoliation reduces evapotranspiration and shade, thus altering boundary layer moisture and energy fluxes that drive the local water cycle, for many months after tropical cyclone passage. Understanding the potential for any hydrometeorological impacts arising from such abrupt land surface change is important for guiding future post-hurricane preparedness and recovery planning in coastal communities.

This thesis investigates spatial and temporal changes in defoliation-related precipitation and cloud activity in the month following Hurricane Michael’s (2018) passage through Florida, as well as the potential modification of flash flood frequency one year following the storm. Two Weather Research and Forecasting (WRF) model, version 3.8, simulations are employed to determine the degree to which defoliation from Michael alters heat fluxes, temperature, relative humidity, cloud fraction, and precipitation during the one-month post-storm study period near the storm’s track. A preliminary analysis of historical flash flood reports is also performed to assess relative changes in flash flood frequency near the defoliated area during the year after landfall.

In the month following Michael, modeled 2-m temperature increased by 0.7 C°, with the greatest temperature change occurring at night, and sensible heat flux increased by 8.3 W m-2. Average relative humidity decreased from 73% to 70.1%, and latent heat flux decreased by an average of 13.9 W m-2. The discrepancy between the decrease in latent heat flux and increase in sensible heat flux approximately matches the increased daytime downward ground heat flux. Additionally, the defoliated simulation demonstrated decreased low-cloud fraction while mid-level cloud cover showed an increasing trend, indicating a potential ascension in the cloud base height. Coupled with the reduction in relative humidity, this suggests that with less near-surface moisture, air parcels needed to ascend higher to reach saturation. Precipitation accumulation change is insignificant when averaged over one month, yet evidence of redistribution nearest Michael’s track is found.

Committee Chair

Miller, Paul W.

DOI

10.31390/gradschool_theses.5333

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