Effects of hurricane Wilma on the surface energy partitioning of mangroves in the Florida Everglades

Open Access
Author:
Sarmiento, Daniel Perez
Graduate Program:
Meteorology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 10, 2010
Committee Members:
  • Jose Dolores Fuentes, Thesis Advisor
Keywords:
  • hurricane disturbance
  • Evapotranspiration
  • mangrove
  • tropical forest
  • surface energy
Abstract:
The surface energy partitioning of a mangrove forest in the Florida Everglades was studied. The mangroves of the Florida Everglades are affected by a yearly cycle of dry and wet seasons. The first part of this study aimed to find the effects of the dry and wet seasons on the surface energy fluxes of the mangrove forest. The transition from the wet to dry season caused changes in the partitioning of energy into turbulent fluxes. Increases in the latent heat flux over the forest were observed in the wet season due to the increased availability of water and decreased air temperatures. The decoupling coefficient for the mangroves stayed relatively constant throughout the year, with an average range of 0.80 and 0.95, similar to other mangrove and tropical ecosystems. The strong decoupling between the forest and the atmosphere conveys that the net radiation is the main driver of the latent heat fluxes in the ecosystem. This strong decoupling is common in other mangrove and tropical forests. When the net radiation dropped below 400 W m-2 in the wet season, the latent heat flux was below 150 W m-2, regardless of vapor pressure deficit (VPD) values. In the dry season, the net radiation threshold was 550 W m-2, which was expected due to the overall drop in latent heat fluxes in the dry season. VPD had a higher influence on latent heating rates in the dry season but the latent heat flux (LE) controls were still dominated by the net radiation. Hurricane Wilma (October 2005) passed over the research site which gave us the unique opportunity to calculate the surface energy and latent heat fluxes before and after a hurricane disturbance. The second part of the study focused on how the surface energy fluxes were affected by this disturbance and why these changes occurred. After the hurricane disturbance, the aerodynamic resistance was reduced from an average of 30 s m-1 to 15 s m-1. Satellite data implies that the mangrove forest has recovered from the hurricane. The aerodynamic resistance, however, has remained at about half of what was calculated before the disturbance. The changes in the aerodynamic resistances after the disturbance showed that the structure of the mangrove forest canopy was altered, changing the surface energy dynamics of the ecosystem. Comparing the data from 2004 to 2007, a stronger energy closure was measured during the dry season after the disturbance. Latent heat fluxes increased after the hurricane; these increases were due to the domination of evaporation processes in this ecosystem when the LAI was low. The ecosystem became more coupled to the atmosphere after hurricane Wilma, where the decoupling coefficient dropped to a range of 0.35 to 0.65 in the years after the disturbance.