Dekadal Actual Evapotranspiration (ET)
Available Tools
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Product Documentation
SSEBop Actual Evapotranspiration Products
(Version 5.0, February 2021)
Evapotranspiration (ET), for the most part, is the combination of transpiration from vegetation and evaporation from soil surfaces.
Actual ET (ETa) is produced using the Operational Simplified Surface Energy Balance (SSEBop) model (Senay et al., 2013) for 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 Moderate Resolution Imaging Spectroradiometer (MODIS) thermal
imagery, acquired every 10 days, with reference ET using a thermal index approach. The unique feature of the SSEBop parameterization is that it
uses a pre-defined, seasonally and spatially dynamic surface psychrometer parameter to calculate ET fraction as the difference between observed
LST (dry-bulb) and a cold/wet boundary condition (wet-bulb) using the principle of satellite psychrometry (Senay, 2018). The original formulation
of SSEB is an adaptation of the hot and cold pixel principle of SEBAL (Bastiaanssen et al., 1998) and METRIC (Allen et al., 2007) models.
A recent evaluation of the global ETa product shows promising performance of ETa Anomaly for drought monitoring purposes while water budget studies,
requiring absolute magnitudes, may need to apply a local/region-specific bias correction procedure (Senay et. al, 2020).
ETa data and anomaly products
(current vs. 2003 – 2015) are available at: https://earlywarning.usgs.gov/fews.
The actual ET data unit is millimeters (mm) and the associated color ramp (see Figure 1a.) is available for download as a .style file for ArcGIS and as txt file with RGB color codes. The SSEBop_symbology folder includes instructions on how to add the color ramp in ArcMap and further suggestions on the data visualization.
The anomalies are the ratio of ETa and the corresponding median ETa, expressed as a percent value and have the color ramp (see Figure 1b.) attached. The color ramp, txt file with RGB color codes, and colormap file (.clr) are available in the SSEBop_symbology folder.
Figure 1a.
Figure 1b.
Listed below are all ET products offered:
Yearly ET products:
ET data products as graphics (.png and .pdf), as well as .tif
file. The associated color ramp is available as download on the website.
ET anomaly products for every year as graphics
(.png and .pdf), as well as .tif including the color ramp.
Monthly ET products:
ET data products for every month in a year as graphics (.png and .pdf),
as well as .tif file. The associated color ramp is available as download on the website.
ET anomaly products for every month in a
year as graphics (.png and .pdf), as well as .tif file including the color ramp.
Dekadal (10 day) products:
ET data products for every dekad in a year as graphics (.png and .pdf),
as well as .tif file. The associated color ramp is available as download on the website.
ET anomaly products for every dekad in a year as
graphics (.png and .pdf), as well as .tif file including the color ramp.
Cumulative ET anomaly products:
ET anomaly products are cumulative in intervals of dekads and grouped
by the region's main growing season(s).
ET anomaly products for every dekad in a year as graphics (.png and .pdf), as well as .tif file including the color ramp.
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.
https://www.sciencedirect.com/science/article/abs/pii/S0022169498002534
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.
https://www.mdpi.com/1424-8220/7/6/979
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.
https://www.sciencedirect.com/science/article/abs/pii/S0378377410003355?via%3Dihub
Senay, G. B., Bohms, S., Singh, R. K., Gowda, P. H., Velpuri, N. M., Alemu, H., & Verdin, J. P. (2013). Operational evapotranspiration mapping using remote sensing and weather datasets: A new parameterization
for the SSEB approach. JAWRA Journal of the American Water Resources Association, 49(3), 577-591.
https://onlinelibrary.wiley.com/doi/full/10.1111/jawr.12057
Senay, G. B. (2018). Satellite psychrometric formulation of the Operational Simplified Surface Energy Balance (SSEBop) model for quantifying and mapping evapotranspiration. Applied Engineering in Agriculture, 34(3), 555-566.
https://elibrary.asabe.org/abstract.asp?AID=48975&t=3&dabs=Y&redir=&redirType=
Senay, G. B., Kagone, S., & Velpuri, N. M. (2020). Operational Global Actual Evapotranspiration: Development, Evaluation and Dissemination. Sensors, 20(7), 1915.
https://www.mdpi.com/1424-8220/20/7/1915