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Evapotranspiration Network in Florida

Project Chief: Barclay Shoemaker, Mike Wacker
Cooperators: Miami Dade County, Priority Ecosystem Studies, Reedy Creek Improvement District, South Florida Water Management District, Southwest Florida Water Management District, St Johns River Water Management District, Tampa Bay Water
Period of Project: October 2000 Current

Problem Statement

Micrometeorological station at Starkey pasture, Pasco County, Florida.

Micrometeorological station at Starkey pasture, Pasco County, Florida.


Evapotranspiration (ET) is a large part of the hydrologic budget in Florida, ranging from 30 to over 100% of average precipitation. In the past, the accuracy of hydrologic models, basin-scale studies, water budgets, and other hydrologic analyses throughout the State was reduced because of the lack of accurate estimates for this large water loss. Scientists and water managers in Florida would benefit from having a network of consistently operated high-quality ET stations from representative land use areas using state-of-the-science methods. Another recurring problem in hydrologic simulation and water allocation strategies in Florida has been inconsistencies between the five State of Florida Water Management Districts in methods for computing the potential and reference ET. Potential ET (PET) is a necessary data input for most hydrologic simulation models. Reference ET (RET) is a necessary input for WMD water allocation to water users.

Objectives

1) Measure actual ET from representative land covers in Florida

2) Develop predictive models to estimate ET from environmental variables such as depth to water, season, and net radiation

3) Provide 2-km gridded satellite-based estimates of potential and reference ET on a daily time scale for the entire State

Components of the surface-energy balance used to estimate evapotranspiration.

Components of the surface-energy balance used to estimate evapotranspiration.


Approach

For ET stations, evapotranspiration and other variables are measured for between 2 and 10 years to develop relations between measured ET and environmental factors such as weather, groundwater levels, and plant cover conditions. Data collected included:

  • Sensible and latent heat (ET) fluxes using high-frequency eddy-covariance systems (KH2O krypton hygrometer and CSAT3 3-D sonic anemometer);
  • Solar, net, and incoming and outgoing short and long-wave radiation;
  • Air temperature, relative humidity, wind speed and direction, soil heat flux, temperature, and water content; and
  • Depth to water and rainfall.


  • The following site types were measured: lake, estuary, shallow and deep water-table pasture, hay field, pine forest, wetland forest, cypress, wet prairie, marsh, citrus, sawgrass, palmetto/scrub, and urban land use.

    For the satellite-based gridded PET and RET, a method was developed that converts Geostationary Satellite System (GOES)-satellite solar radiation data to these commonly used ET estimates; the approach was validated using PET and RET from the ground-based sites.

    Results

    Annual ET rates at land-based sites vary from a low of 570 mm (22.4 inches) at a pasture with a deep water table to 1340 mm (53 inches) at a sawgrass marsh. Rates at open-water sites exceed 1500 mm (59 inches). Daily values of ET are archived in the USGS NWIS database and can be accessed at https://fl.water.usgs.gov/et/etdata.html

    The daily PET and RET datasets, by year and county from 1995 through 2010, can be accessed at https://fl.water.usgs.gov/et/

    Information Products

    Shoemaker, W. B., Lopez, C. D., Duever, M. J., 2011, Evapotranspiration over spatially extensive plant communities in the Big Cypress National Preserve, southern Florida, 2007-2010: https://pubs.usgs.gov/sir/2011/5212/

    Sumner, D.M., 2001, Evapotranspiration from a Cypress and Pine Forest Subjected to Natural Fires in Volusia County, Florida, 1998-99: U.S. Geological Survey Water-Resources Investigations Report 01-4245, 55 p.

    Shoemaker W.B., S. Huddleston, A.M. O'Reilly, and C. Boudreau, 2008. Sensitivity of wetland saturated hydraulic heads and water budgets to evapotranspiration, Wetlands, Vol. 28, No. 4, December 2008, pp. 1040-1047.

    Shoemaker W. B., D. M. Sumner, and A. Castillo, 2005, Estimating changes in heat energy stored within a column of wetland surface water and factors controlling their importance in the surface energy budget, Water Resources Research, 41, W10411, doi:10.1029/2005WR004037.

    Shoemaker W.B., and D.M. Sumner, 2006, Alternate corrections for estimating actual wetland evapotranspiration from potential evapotranspiration, Wetlands, Volume 26, No. 2, pp. 528 – 543.

    Mecikalski, J. R., Sumner, D. M., Jacobs, J. M., Pathak, C. S., Paech, S. J., and Douglas, E.M., 2011, Use of Visible Geostationary Operational Meteorological Satellite Imagery in Mapping Reference and Potential Evapotranspiration over Florida: in Evapotranspiration, edited by Leszek Labedzki, Intech, https://www.intechopen.com/books/show/title/evapotranspiration, 26 p.

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