Annual variant of tmr_partition. Built from points rarefied with
time_cols = "year" only (one point per pixel per year) and
extracted against annual predictors. Predictors attached to each point
are forest_cover, pr_ann (annual precipitation), and
elevation, all z-scored. Uses
n_spatial_folds = 2 and n_temporal_folds = 2 for four
folds. Loaded with data(tmr_partition_annual).
tmr_partition_annualA list as returned by spatiotemporal_partition.