Quick note (and correction):
The black line is meant to show the median which, for any given winter day, we can expect to be zero. What I like about the median is that it does such a good job of showing exactly when the summer rainy season starts and ends.
Keep in mind the median line doesn't do justice to winter dry season rains. However, it does highlight the point that those winter rain events are unpredictable (i.e. anomalous) compared the the reliable daily occurrence of rain in the summer.
One last point: the graph is normalized in a sense to show "weekly" rain but doing it as a 7-day running total. Thus, each line (both blue fill and black line) are constructed 365 points per year with each point being the 7-day running total (not average).
The vertical axis is incorrectly labeled: it should read "as a 7 day running total."