This seems to be what he is referring to by the map's subjectivity: https://droughtmonitor.unl.edu/About/WhatistheUSDM.aspx https://droughtmonitor.unl.edu/Abou

This seems to be what he is referring to by the map's subjectivity: https://droughtmonitor.unl.edu/About/WhatistheUSDM.aspx https://droughtmonitor.unl.edu/About/WhatistheUSDM.aspx > Who draws the map? > Several authors from the NDMC, NOAA and USDA create the map. They take turns, usually two weeks at a time. > How do they figure out where and how bad drought is? > This is what makes the U.S. Drought Monitor unique. It is not a statistical model, although numeric inputs are many: [...]