High Resolution Daily Global Alfalfa-Reference Potential Evapotranspiration Climatology

Global alfalfa-reference potential evapotranspiration (ETr) is a key model parameter in actual evapotranspiration (ETa) modeling for worldwide applications. This dataset was constructed for use with the Operational Simplified Surface Energy Balance (SSEBop) model as a key driver of the final ETa magnitude. SSEBop is a parametric energy balance-based model that determines actual ET as the product of two independent estimates: 1) the SSEBop modeled ET fraction (ETf), an index nominally varying between 0 and 1 and derived from observed Landsat surface temperature using satellite psychrometry, and 2) the potential ET (maximum) under environmental conditions for an alfalfa crop (in millimeters). As SSEBop ETf can now be modeled for any Landsat scene across the globe, a suitable global ETr climatology dataset needed to be created. This global ETr data is a fusion of several different remote sensing and modeling products: 1981-2010 climatological normal (daily mean) ETr from Gridmet over the continental United States and 1981-2010 climatological normal MERRA-2 Fine Resolution ETr for all areas outside of the continental United States that has been scaled and corrected via terrestrial ecoregions from OneEarth and scaled using Worldclim Version 3 ETo (Abatzoglou 2013; Dinerstein et al., 2017; Hobbins et al., 2022; Zomer et al., 2022). The final mosaic has been smoothed and resampled to 1-km spatial resolution. The final dataset is a daily dataset of 366 GeoTIFF raster files for each day of the year including the leap day and representing a climatological normal (1981-2010) alfalfa-reference potential ET (ETr) for the entire global extent. Each raster has been scaled so multiply each day by a factor of 0.01 to scale it to millimeters.