Compute "water" day and year, based on the end of the typical or legal dry season. This is September 30 in California.
waterDayYear(d, end = "09-30")
anything the can be safely converted to
"MM-DD" notation for end of water year
data.frame object with the following
the "water year"
the "water day"
This function doesn't know about leap-years. Probably worth checking.
# try it waterDayYear('2019-01-01') #> wy wd #> 1 2019 93