Actual evapotranspiration (ET) estimation using remote sensing and weather data is an active research activity by U.S. Geological Survey (USGS) scientists interested in delivering consistent and useful nationwide ET information. This information is important when measuring critical hydrologic components of the water budget for agricultural and natural landscapes across space and time. In recent years, the uncharted impacts of prolonged drought on limited national water resources have highlighted the need for timely and more accurate consumptive use data at the field- and basin-scale, which can now be readily achieved through Landsat-based ET modeling capabilities.
Scientists at the USGS Earth Resources Observation and Science (EROS) Center are combining Landsat collection thermal capabilities, cloud computation efficiencies, and new model parameterization improvements to advance the Operational Simplified Surface Energy Balance (SSEBop) model for the future of ET mapping nationwide and beyond. Previously, evaluation of SSEBop ET estimation across the conterminous United States (CONUS) has allowed for assessment of water balance understanding at broad scales. Recently, model enhancements and performance against prior versions include the additions of Landsat 9 (launched September 2021), global model extensibility, and an improved parameterization of SSEBop using a novel approach called the Forcing and Normalizing Operation (FANO) to better estimate ET in all landscapes and seasons. As such, the FANO parameterization demonstrates more product accuracy and domain scalability for multiyear SSEBop ET applications.
An independent Water Balance ET (WBET) generated using more than 1,000 sub-basins was compared with SSEBop ET at the water-year (October 1 – September 30) timestep. This nationwide multiyear (2009, 2011, 2013, 2016, 2018) analysis included both wet and dry years for ET comparisons grouped across six different hydro-climatic regions of CONUS. Using SSEBop summaries with WBET, results indicate the improved performance of SSEBop (FANO) over the previous version of SSEBop. Bias is reduced from 48 millimeter/year (7%) to –8 millimeter/year (–1%) for the 5-year average at CONUS scale. Individual water-year comparisons show SSEBop is within 5% for all water-years at all regions.
The EROS Center develops and openly shares these ET products with various Federal and State partners and the public. The data are also critical input components in the USGS National Hydrologic Model (NHM) infrastructure system for efficient construction of national-scale water accounting information. The associated manuscript is available here.
Annual Total Water-Year SSEBop Actual Evapotranspiration using 5-year median (2009, 2011, 2013, 2016, 2018) data from Landsat. No Data values represent isolated areas with missing model auxiliary input data. The associated manuscript is available here.
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