Project Summary Sheet

Project Title: Evapotranspiration Measurements and Modeling in the Everglades

Project Start Date: October 1994 Project End Date: September 2005

Web Sites: http://sofia.usgs.gov

Location (Subregions, Counties, Park or Refuge): Southern Everglades, Dade and Monroe Counties

Funding Source: USGS's Greater Everglades Science Initiative (PBS)

Principal Investigator(s): Edward R. German, egerman@usgs.gov, 407-865-7575

Project Personnel: Sandra Kinnaman, kinnaman@usgs.gov, 407-865-7575; Eddie Simonds, simonds@usgs.gov, 407-865-7575

Supporting Organizations: USGS

Associated / Linked Projects: None

Overview & Objective(s): Evapotranspiration (ET) is one of the most important components of the Everglades water budget. The principal objective of the study is to develop an understanding of ET within the Everglades drainage unit, excluding agricultural and brackish environments. To achieve this, a network of ET-measurement sites was established in the Everglades in 1996, representing the various types of hydrologic and vegetative environments. Eight sites were operated in 1996 and nine sites were operated in 1997. Data from these sites was used to characterize ET and other meteorological conditions in the Everglades, and to develop models of ET as a function of solar radiation and water level. A report describing these findings was published in 2000. Data collection continued at selected sites during 1998-2000 to provide data for other studies involved with understanding water levels and flows in the Everglades. In 2000, new sites were established in Shark Valley Slough, to test transferability of models developed using 1996-97 data, and to refine the understanding of factors related to ET.

Status: Presently, six ET sites are operational in the Everglades National Park. Data are being processed and models of ET are being developed.

Recent & Planned Products: A paper was presented at 2nd Federal Interagency Hydrological Modeling Conference in Las Vegas, NV in August 2002. A paper was presented at the GEER conference in April 2003. Papers are planned for 2004, and a final comprehensive report describing all data and conclusions is planned to wrap up the study in 2005.

Relevance to Greater Everglades Restoration Information Needs: Information provided by this project and other projects that make use of the data and findings will be used by restoration and resource managers for evaluation of management alternatives. The project supports directly or indirectly many of the Science Objectives given in the draft USGS Science Plan in Support of Everglades Restoration. Specifically, the Everglades ET project directly supports objective SO1 under Section 1A of Restoration Goal 1 (How does the Everglades ecosystem function, including evapotranspiration rates?). Indirectly, Everglades ET supports Science Objectives 2A:SG5, 2B:SG5, and 2C:SG5 under Restoration Goal 2, and SG5 under Restoration Goal 3, by providing the data and models of ET that will be necessary for use of hydrological and ecological models required by these objectives. Also, Everglades ET data and models are necessary for operation of the Landscape scale models to be implemented according to Section VI of the draft DOI Everglades Restoration Science Prioritization Strategy document.

Key Findings:

• Models based on the Priestley-Taylor principles can be used to estimate ET as a function of water depth, incoming solar energy, and net available energy. In the absence of data on net available energy, air temperature and water depth data can be used to estimate net available energy.
• ET is related to water depth, with lowest ET for a given energy input occurring when water levels are below land surface.
• Based on data from nine sites in the natural Everglades system, ET ranges from about 42 in/yr in drier locations to as high as 57 in/yr in open-water areas.
• Generally, the most important factor related to ET is incoming solar and atmospheric radiation. However, storage of heat in water can contribute substantial amounts of energy to ET for short time periods (one or two days) during passage of cold fronts.
• The leaf area of emergent vegetation does not seem to be directly related to ET rates. The highest ET rates occurred at open-water sites or sites with relatively sparse emergent vegetation. The presence of dead material in the plant canopy promotes sensible heat transport rather than latent heat transport, thereby lowering the amount of available energy for ET.