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SSEBop Evapotranspiration Anomaly Products
(March 2014)

Evapotranspiration (ET) is the combination of transpiration from vegetation (through the root system) and direct evaporation from soil-vegetation-water surfaces. Actual ET (ETa) is produced using the Operational Simplified Surface Energy Balance (SSEBop) model (Senay et al., 2013) for the period 2003 to present. The SSEBop setup is based on the Simplified Surface Energy Balance (SSEB) approach (Senay et al., 2007, 2011) with unique parameterization for operational applications. It combines ET fractions generated from remotely sensed MODIS thermal imagery, acquired every dekad (10-day), with reference ET using a thermal index approach. The unique feature of the SSEBop parameterization is that it uses pre-defined, seasonally dynamic, boundary conditions that are unique to each pixel for the “hot/dry” and “cold/wet” reference points. The original formulation of SSEB is based on the hot and cold pixel principles of SEBAL (Bastiaanssen et al., 1998) and METRIC (Allen et al., 2007) models. The SSEBop model has been validated comprehensively in the conterminous U.S. using eddy covariance flux tower ET, basin water balance ET and in comparison with MOD16 ET by Velpuri et al. (2013) and also against lysimeters by Senay et al. (2014).

ETa anomaly products (current vs. 2003 - 13) are available at the following: http://earlywarning.usgs.gov/fews/global/. The anomalies are the ratio of ETa and the corresponding median ETa, expressed as a percent value. Arid regions with little or no vegetation (maximum NDVI < 0.25) are replaced with precipitation values for the corresponding period. In arid climates the magnitude of actual ET can be approximated by precipitation.

Legend

Listed below are all ETa anomaly products offered:

Monthly ETa products:
ETa anomaly products for every month in a year.

Cumulative ETa anomaly products:
ETa anomaly products are cumulative in intervals of dekads and grouped by the region's main growing season(s).


References:
Allen, R.G., Tasumi, M., Trezza, R., 2007. Satellite-based energy balance for mapping evapotranspiration with internalized calibration (METRIC) – Model. ASCE J. Irrigation and Drainage Engineering 133, 380-394.

Bastiaanssen, W.G.M., M. Menenti, R.A. Feddes, and A. A. M. Holtslag, 1998. The surface energy balance algorithm for land (SEBAL): Part 1 formulation. Journal of Hydrology 212–213: 198–212.

Senay, G.B., M. Budde, J.P. Verdin, and A.M. Melesse, 2007. A coupled remote sensing and simplified surface energy balance approach to estimate actual evapotranspiration from irrigated fields. Special issue: Remote sensing of natural resources and the environment. SENSORS, 1, 979-1000.

Senay, G.B., M. Budde, J.P. Verdin, 2011. Enhancing the Simplified Surface Energy Balance (SSEB) approach for estimating landscape ET: Validation with the METRIC model. Agricultural Water Management, 98: 606-618.

Senay, G.B., S. Bohms, R.K. Singh, P.H. Gowda, N.M. Velpuri, H.Alemu, and J.P. Verdin, 2013. Operational evapotranspirationmapping using remote sensing andweather datasets: A new parameterization for the SSEB approach. Journal of the American Water Resources Association, 1–15, http://dx.doi.org/10.1111/jawr.12057.

Senay, G.B., P.H. Gowda, S. Bohms, T.A. Howell, M. Friedrichs, T.H. Marek, and J. P. Verdin, 2014. Evaluating the SSEBop approach for evapotranspiration mapping with landsat data using lysimetric observations in the semi-arid Texas High Plains Hydrol. Earth Syst. Sci. Discuss., 11, 723–756, 2014. www.hydrol-earth-syst-sci-discuss.net/11/723/2014/ doi:10.5194/hessd-11-723-2014.

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