!--------1---------2---------3---------4---------5---------6---------7---------8
subroutine fdm_explicit_water 
!--------1---------2---------3---------4---------5---------6---------7---------8
  use global_constants, only : rkind, dt, volume_ratio_rock, time, year
  use global_parameters, only : irmax, dr, temperature_initial,iau, temp, radius
  use heat_parameters, only : thermal_conductivity, thermometric_diffusivity 
  use material_parameters, only : mn, iw, ir, ii, material_check, material_select
  use ice_parameters, only : temperature_melting_I
  use energy, only : set_energy, temp_old
  implicit none
  integer :: i
  real(rkind) :: coef, heat_decay, coef_rad_rock, dtr
  dtr = dt/(dr*dr)
  temp(ir+2:iw) = temperature_melting_I
  do i = iw+1, irmax-1
    call material_select(i)
    coef = thermometric_diffusivity(mn(i))*dtr/real(i)
    temp(i) = temp_old(i) + coef*(real(i+1)*temp_old(i+1) &
      & -2._rkind*real(i)*temp_old(i)+real(i-1)*temp_old(i-1)) &
      & + heat_decay(time,i)*dt*thermometric_diffusivity(mn(i)) &
      & /thermal_conductivity(mn(i))
  enddo
  temp(irmax) = temperature_initial(iau)
  call fdm_explicit_water_rock(temp_old,dtr)
  return
end subroutine fdm_explicit_water