Average HFMD infection occurrence against total rainfall (RF), NRF in equation (1), and its least squares fitting curve, XRF(r). XRF(r) in equation (6), solid line; NRF, dashed line. (a) Hokkaido, (b) Miyagi, (c) Tokyo, (d) Nagano, (e) Kyoto, (f) Kochi, (g) Fukuoka, and (h) Okinawa.