subroutine alph
c
c     + + + PURPOSE + + +
c     Computes alpha, a dimensionless parameter that expresses the fraction 
c     of total rainfall that occurs during 0.5 ho.
c
c     + + + COMMON BLOCKS + + +
      include 'cbk3.inc'
c      read: ida
c     ida         - Julian Day of Year.  Used as a subscript to R.
c
      include 'cbk4.inc'
c      read: mo
c     mo          - The current month (1=Jan, 2=Feb...).
c
      include 'cbk5.inc'
c      read: r
c     r           - Daily Precipitation amount (inches of water)
c
      include 'cbk7.inc'
c      read: k7
c     k7          - Seed for random number generation.
c
      include 'cbk9.inc'
c      read: wi,ab,ab1,rn1
c      write: r1
c     wi          - Average Maximum .5 Hour Precip. Intensity (by month)
c     ab          - Set to 0.02083, and used to calculate AI
c     ab1         - Set to 1.0-ab, and used to calculate AI
c     rn1         - ??? -- used for precip gamma dsn
c
c     + + + LOCAL VARIABLES + + +
      real ai, ajp, ei

c     + + + FUNCTION DECLARATIONS + + +
      real dstg
c
c     + + + END SPECIFICATIONS + + +
c
      ei=r(ida)-sml
      ai=ab1/(wi(mo)-ab)
      if (ei.lt.1.0) then
        ajp=1.0
      else
        ajp=1.0-exp(-5.0/ei)
      endif
      r1=dstg(ai,k7,rn1)
      r1=(ei*(ab+r1*(ajp-ab))+sml*ab)/r(ida)
      return
      end