發 and 髮 have been simplified into one single character: 发.
发 contains the separate meanings of 發 and 髮 but differentiates by tone: fa1 (fā) and fa4 (fà).
Most topolects (西安，武汉，洛阳，乌鲁木齐，贵阳，济南，柳州，万荣，etc.) don't have a tonal differentiation and 发 only has one pronunciation.
What is the origin of the tonal differentiation in Mandarin?