I came across many topic for increasing subtitle fonts but none addresses my question. I want to increase the font size of the subtitle (i.e., 2011, 2014 etc) of each graph. These subtitles are added automatically as they are part of my data.frame (and I used facet function to use the Year column). I have tried a few different things but none worked. here is a sample code that would produce the attached graph.
ggplot(map_and_data)+
geom_sf(aes(fill=SPEI))+
facet_wrap(~ Year)+
scale_fill_gradient(low = "yellow", high = "blue")+
theme_bw()+
theme(axis.text = element_text(size=14), plot.subtitle = element_text(size = 20))+
theme(legend.position = "bottom", legend.title = element_blank(), legend.key.width = unit(3,"cm"), legend.text = element_text(size=18))
the plot.subtitle
did not work.