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SSEBop Evapotranspiration Anomaly Products
(Version 2.0, April 2013)

Evapotranspiration (ET) is the combination of transpiration from vegetation and evaporation from soil. Actual ET (ETa) is produced using the operational Simplified Surface Energy Balance (SSEBop) model (Senay et al., 2013) for the period 2000 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 8 days, with reference ET using a thermal index approach. The unique feature of the SSEBop parameterization is that it uses predefined, 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.

ETa anomaly products (current vs. 2001 – 2010) are available at the following: http://earlywarning.usgs.gov/fews/africa/index.php. 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.



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 8-day periods and grouped by major growing seasons:
  • September – June – Southern Africa growing season
  • September – January – East Africa growing season (short rains)
  • May – December – East Africa (long rains, Ethiopia) and West Africa growing season
  • January – July – East Africa growing season (long rains)


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. Singh, P.A. Gowda, N.M. Velpuri, H. Alemu and J.P. Verdin, 2013. Operational evapotranspiration mapping using remote sensing and weather datasets: A new parameterization for the SSEB approach. Journal of American Water Resources Research. In Press.