Evapotranspiration (ET) is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and water bodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves. Potential evapotranspiration (PET) represents the evapotranspiration rate from a given surface without moisture limitation. Reference evapotranspiration (RET) is a representation of evapotranspiration from a hypothetical reference crop such as a green grass surface with a uniform height of 12 cm, actively growing, well-watered, and completely shading the ground. PET is used extensively in hydrologic modeling whereas RET is used primarily in agricultural, irrigation and regulatory applications. Solar radiation is the primary driving force in the ET process.
A model has been developed to produce PET and RET estimates over Florida using solar radiation obtained from Geostationary Operational Environmental Satellites (GOES) and climate data from the Florida Automated Weather Network, the State of Florida Water Management Districts and the National Oceanographic and Atmospheric Administration. The model was created through a jointly funded project involving the five Florida Water Management Districts, the University of New Hampshire (UNH), and the University of Alabama at Huntsville (UAH), and the US Geological Survey (USGS). The Priestley-Taylor and American Society of Civil Engineers reference ET equations provide daily PET and RET estimates respectively on a 2 km grid spatially distributed over the State of Florida beginning in 1995.
EDEN staff receives ET data annually from the USGS approximately six months after the end of the calendar year. Daily PET values (in millimeters) are extrapolated by location for each of the EDEN water level stations and assembled into Excel spreadsheets organized by area. The period of record begins on June 1, 1995 and data for each subsequent year is added as it becomes available, generally on an annual basis.
For more information about the estimated ET data from the USGS and others download the report "Satellite-based Solar Radiation, Net Radiation and Potential and Reference Evapotranspiration Estimates Over Florida." (Available at http://hdwp.er.usgs.gov/ET/GOES_FinalReport.pdf. Please note, this is a 2.2 MB PDF file and requires the free Adobe Acrobat Reader.) To access PET and RET data by county, please visit the USGS Hydrologic Data Portal. (Data is available for 1995-2004 and 2005-2007.)
For more information about EDEN (Everglades Depth Estimation Network), visit the links to the right. If you would like to receive notifications when new ET is available, please sign up for our free newsletter.