Basically there are two definitions of poverty with two crowds of followers.
1. People are poor if they can't afford (basic) things. People are very poor if they go hungry to bed.
2. People are poor if they earn less [1] than the average (not median) household. From the article "The report looked at the gap between the income of the poorest Japanese families with children and the average household income."
When does the poverty rate rise in 1. and 2.?
1. When peoples (real) income decreases (e.g. they lose jobs) and they can't afford (basic) things they could afford 10 years before. Or prices are rising to the same effect. The margin between income and costs gets smaller.
2. When some people get a lot richer (e.g. the "1%") then the income average rises and the poverty rate rises, although "poor" people might also have higher income or can afford more things than 10 years before (because of cheaper food, clothes, phone costs, energy they have more "disposable income").
I wish we would label these two types of poverty differently to have better discussions.
[1] EDIT: a certain percentage