After taking a close look at the 1970-2000 period, I wanted to post some results from other 30 year periods (first available NOAA gridded pop data for the US is 1930). There is some overlap, since we don’t have 90 years of population data, so I’m choosing to use 1930-1960 and 1950-1980 in addition to the 1970-2000 tests already done. One benefit is that since most of the CRS to MMTS transitions occurred after 1980, I did not need to control for these changes in my pairwise comparisons (although there may be other inhomogeneities causing issues).
Anyhow, here are the results for using log (popWithin10km+25) and log(PopWithin1km+25) for each of the two periods:
I suppose the interesting notes here are that there is a much clearer signal in the 1950-1980 period than in that 1930-1960 period, and that neither of these show a UHI signal to the degree that’s present in 1970-2000. Furthermore, in both of these scenarios, the 1km radius for population density results in a slightly better correlation.