To characterize historical droughts in the conterminous United States (CONUS), we estimated the actual evapotranspiration (ETa) in the CONUS using the generalized complementary relationship (GCR) for 1895-2016. The ETa estimates were compared against simulations from the Noah land surface model (LSM). In this study, the evapotranspiration (ET) deficit defined as the difference between the wet-environment ET (ETw) and ETa was then normalized to calculate the Standardized Evapotranspiration Deficit Index (SEDI) across the CONUS for the years 1895-2016. The SEDI was compared to the Standard Precipitation Index (SPI) at various time scales. The results showed that the GCR ETa was slightly higher than the Noah LSM-simualted ETa. As time scales increased, the correlation between the SEDI and the SPI was higher. This study suggests that the GCR has promise as a tool in the estimation of ETa and SEDI can be useful for the drought characterization.