Actual Evapotranspiration for Florida

Science Center Objects

Evapotranspiration is a large component of the Florida water budget – generally second only to rainfall, but exceeding rainfall and all other components during droughts. The prominence of evapotranspiration highlights the need to accurately quantify this hydrologic component in quantitative analyses of watershed hydrology.  Spatio-temporal estimates of evapotranspiration throughout Florida are available from existing and freely-available, long-term global remote sensing-based products; however, the utility of these products for the Florida environment has not been assessed. Without quantitative assessment of the error and biases of the available evapotranspiration products, their enormous potential in adding to the integrity of ongoing hydrologic analyses remains unexploited. 

Objectives

The Actual Evapotranspiration (AET) work addresses the following objectives:

  • Quantitatively assessing the utility of available actual spatio-temporal evapotranspiration products in the Florida environment relative to independent measurements/estimates of Florida evapotranspiration for basins in all five Water Management Districts (SRWMD, NWFWMD, SJRWMD, SWFWMD, SFWMD) and Tampa Bay Water (TBW).
  • Evaluating the efficacy of "customizing" the available AET products to the Florida environment to compensate for any persistent biases and errors in those products.

 

Methods

Work being performed by USGS includes:

  1. The USGS Simplified Surface Energy Balance—Operational (SSEBop; Senay et al., 2008, 2013) is being assessed for its utility in the Florida environment in a manner similar to that of Velpuri et al. (2013).
     
  2. A second daily spatio-temporal AET product will be developed and evaluated within this study based on the traditional "crop" coefficient method, using 8 generalized land use categories: Urban, Open water surface, Forest, Grass, Marsh, Sawgrass, Cypress swamp, and Agriculture in a similar manner as described by Sumner et al. (2017).
     
  3. The utility of the two spatio-temporal AET datasets described above is used to compare with the following independent measurements/estimates of evapotranspiration at the monthly timescale:
    • Watershed-based estimates of actual evapotranspiration.
    • Micrometeorological-based estimates of actual evapotranspiration.
       
  4. To facilitate “seamless” use of the proposed AET product in regional analyses of the Floridan Aquifer, the product will be quality-assured using available data (primarily water budgets) sources in those parts of other states underlain by the Floridan Aquifer.
     
  5. "Customization" of the evaluated freely-available spatio-temporal AET products involves the identification of systematic biases and errors in these products relative to the independent measures of evapotranspiration followed by proposed corrections for these discrepancies (e.g., as already identified for open water surfaces and near coastal areas).

 

Basins in east-central Florida in the St. Johns River Water Management District

Figure 1. Basins in east-central Florida in the St. Johns River Water Management District for which actual evapotranspiration rates were calculated for the pilot study. These basins included 02232500 (St. Johns River near Christmas basin), 02233484 (Econlockhatchee River basin), 02235000 (Wekiva River basin), 02249007 (Eau Gallie River basin), and 02251000 (South Prong at St. Sebastian River basin). Surficial aquifer wells (bold black circles), stream gaging stations (red triangles), and lakes and streams in the basins are shown.

Basins in northeast Florida in the St. Johns River Water Management District

Figure 2. Basins in northeast Florida in the St. Johns River Water Management District for which actual evapotranspiration rates were calculated for the pilot study. These basins included 02245260 (Deep Creek basin), 02245500 (Black Creek basin), and 02246000 (North Fork Black Creek basin). Surficial aquifer wells (bold black circles), stream gaging stations (red triangles), and lakes and streams in the basins are shown.

References

Sepúlveda, N., 2021, Evaluation of actual evapotranspiration rates from the Operational Simplified Surface Energy Balance (SSEBop) model in Florida and parts of Alabama and Georgia, 2000–17: U.S. Geological Survey Scientific Investigations Report 2021–5072, 66 p., https://doi.org/10.3133/sir20215072.

Sepúlveda, N., 2021, Data sets of actual evapotranspiration rates from 2000 to 2017 for basins in Florida and parts of Alabama and Georgia, calculated using the water-balance method, the bias-corrected Operational Simplified Surface Energy Balance (SSEBop) model, and the and the land-use crop coefficients model: U.S. Geological Survey data release, https://doi.org/10.5066/P99AB3X4.

Velpuri, N. M., Senay, G. B., Singh, R. K., Bohms, S. and Verdin, J. P. (2013). A comprehensive evaluation of two MODIS evapotranspiration products over the conterminous United States: Using point and gridded FLUXNET and water balance ET, Remote Sensing of Environment, 139, 35-49, https://doi.org/10.1016/j.rse.2013.07.013

Sumner, D., Geurink, J. and Swancar, A. (2017). Use of eddy-covariance methods to "calibrate" simple estimators of evapotranspiration, Proceedings of the 2017 ASABE Annual International Meeting, Spokane, WA, July 16-19, 2017, DOI: 10.13031/aim.201700912

Senay, Gabriel B., Stefanie Bohms, Ramesh K. Singh, Prasanna H. Gowda, Naga M. Velpuri, Henok Alemu, and James P. Verdin (2013). Operational Evapotranspiration Mapping Using Remote Sensing and Weather Datasets: A New Parameterization for the SSEB Approach. Journal of the American Water Resources Association (JAWRA), 49(3): 577-591, DOI: 10.1111/jawr.12057

Senay, G. B., Verdin, J., Lietzow, R. and Melesse, M. (2008). Global daily reference evapotranspiration modeling and evaluation. Journal of the American Water Resources Association, 44, 969–979, DOI: 10.1111/j.1752-1688.2008.00195.x