Global Application of Drought Monitoring using the Operational Simplified Surface Energy Balance (SSEBop) Evapotranspiration Dataset

Evapotranspiration (ET) is one of the most important components in the hydrologic cycle and is used by the U.S. Geological Survey (USGS) Famine Early Warning Systems Network (FEWS NET), an activity of the U.S. Agency for International Development (USAID), to estimate water use and crop productivity for drought monitoring. In May of 2021 the latest version (Version 5) of the Operational Simplified Surface Energy Balance (SSEBop) ET was released at https://earlywarning.usgs.gov/fews. It includes improvements such as more detailed coastline and small islands representation; the use of solar radiation data from ERA5-Land (European Center for Medium-range Weather Forecast Reanalysis Version 5) to determine a key model parameter and a merged best-available air temperature data set available globally. We used the SSEBop Version 5 data (2003-2018) to map and characterize actual ET (ETa) at dekadal (~10day), monthly, and annual scales covering several regions across the globe. We compared the estimates with Eddy Covariance Flux Tower measurements, as well as conducted an annual water budget comparison and found that SSEBop ETa captured the temporal variability with a reasonable performance. However, mixed results were obtained in terms of absolute magnitude which varied by region, from under-estimation in Europe and Asia and over-estimation in Africa and Australia, suggesting the need to quantify and apply a region-specific bias correction for water budget applications. The ETa along with the anomaly (percent of normal) products provide a consistent global dataset that can be used to monitor spatiotemporal variability of dry/drought conditions at a relatively high spatial resolution (1 km). USGS FEWS NET uses these data as part of the convergence of evidence to monitor drought and provide early warning to avert potential food-insecurity crises.