German companies typically pay one large dividend in the spring of each year. Shareholders on the official “dividend record date” (abbreviated above as "dividend date") are entitled to the payments, which are usually made the next day. To avoid taxes on the dividends, banks and non-German investors structure short-term loans around these record dates – what’s called “dividend arbitrage.” Stocks are typically loaned over two to 14 days to German investment funds and banks that pay no dividend tax or can claim refunds. This is why demand to borrow shares spikes around the record date.Notice that the authors, Cezary Podkul and Lena Groeger, took some time to explain the methodology behind the story. I believe this ought to become common practice. Just one question: Isn't it weird that the chart doesn't have a scale on the Y-axis? It's not the first time I see this, and it makes me feel uneasy.
UPDATE (h/t Miska Knapek): Germany has closed the tax loophole that enabled these practices. Who said that investigative reporting and visualization have a minimum impact on society?
UPDATE 2: Bob Rudis has replied to my question about missing scales with this excellent article. Please do make some time to read it.