#include <misc.h>#include <preproc.h>subroutine SnowWater(clm)!-----------------------------------------------------------------------!!  CLMCLMCLMCLMCLMCLMCLMCLMCLMCL  A community developed and sponsored, freely!  L                           M  available land surface process model.!  M --COMMUNITY LAND MODEL--  C!  C                           L!  LMCLMCLMCLMCLMCLMCLMCLMCLMCLM!!-----------------------------------------------------------------------! Purpose:! Evaluate the change of snow mass and the snow water onto soil.!! Method:! Water flow within snow is computed by an explicit and non-physical ! based scheme, which permits a part of liquid water over the holding ! capacity (a tentative value is used, i.e. equal to 0.033*porosity) to! percolate into the underlying layer.  Except for cases where the ! porosity of one of the two neighboring layers is less than 0.05, zero ! flow is assumed. The water flow out of the bottom of the snow pack will ! participate as input to soil water and runoff. !! Author:! 15 September 1999: Yongjiu Dai; Initial code! 15 December 1999:  Paul Houser and Jon Radakovich; F90 Revision ! 15 November 2000: Mariana Vertenstein! April 2002: Vertenstein/Oleson/Levis; Final form!!-----------------------------------------------------------------------! $Id: SnowWater.F90,v 1.4.10.2 2002/04/27 15:38:40 erik Exp $!-----------------------------------------------------------------------  use precision  use clmtype  use clm_varcon, only : denh2o, denice  implicit none!----Arguments----------------------------------------------------------  type (clm1d), intent(inout) :: clm	 !CLM 1-D Module!----Local Variables----------------------------------------------------  integer  j                          ! do loop/array indices  real(r8) qin                        ! water flow into the element [mm/s]  real(r8) qout                       ! water flow out of the element [mm/s]  real(r8) wgdif                      ! ice mass after minus sublimation [mm]  real(r8) vol_liq(clm%snl+1 : 0)     ! partial volume of liquid water in layer [-]  real(r8) vol_ice(clm%snl+1 : 0)     ! partial volume of ice lens in layer [-]  real(r8) eff_porosity(clm%snl+1: 0) ! effective porosity = porosity - vol_ice [-]  real(r8) qout_snowb                 ! rate of water out of snow bottom [mm/s]!----End Variable List--------------------------------------------------  if (clm%snl+1 >=1) then     clm%qflx_top_soil = clm%qflx_rain_grnd + clm%qflx_snomelt  else!! Renew the mass of ice lens (h2osoi_ice) and liquid (h2osoi_liq) in the! surface snow layer, resulting from sublimation (frost)/evaporation (condense)!     if (clm%do_capsnow) then        wgdif = clm%h2osoi_ice(clm%snl+1) - clm%qflx_sub_snow*clm%dtime        clm%h2osoi_ice(clm%snl+1) = wgdif        if (wgdif < 0.) then           clm%h2osoi_ice(clm%snl+1) = 0.           clm%h2osoi_liq(clm%snl+1) = clm%h2osoi_liq(clm%snl+1) + wgdif        endif        clm%h2osoi_liq(clm%snl+1) = clm%h2osoi_liq(clm%snl+1) - clm%qflx_evap_grnd*clm%dtime        clm%h2osoi_liq(clm%snl+1) = max(0._r8, clm%h2osoi_liq(clm%snl+1))        clm%qflx_snowcap = clm%qflx_snowcap + clm%qflx_dew_snow + clm%qflx_dew_grnd     else        wgdif = clm%h2osoi_ice(clm%snl+1) + (clm%qflx_dew_snow - clm%qflx_sub_snow)*clm%dtime        clm%h2osoi_ice(clm%snl+1) = wgdif        if (wgdif < 0.) then           clm%h2osoi_ice(clm%snl+1) = 0.           clm%h2osoi_liq(clm%snl+1) = clm%h2osoi_liq(clm%snl+1) + wgdif        endif        clm%h2osoi_liq(clm%snl+1) = clm%h2osoi_liq(clm%snl+1) +  &             (clm%qflx_rain_grnd + clm%qflx_dew_grnd - clm%qflx_evap_grnd)*clm%dtime        clm%h2osoi_liq(clm%snl+1) = max(0._r8, clm%h2osoi_liq(clm%snl+1))     endif!     ! Porosity and partial volume!     do j = clm%snl+1, 0        vol_ice(j) = min(1._r8, clm%h2osoi_ice(j)/(clm%dz(j)*denice))        eff_porosity(j) = 1. - vol_ice(j)        vol_liq(j) = min(eff_porosity(j),clm%h2osoi_liq(j)/(clm%dz(j)*denh2o))     enddo!! Capillary forces within snow are usually two or more orders of magnitude! less than those of gravity. Only gravity terms are considered. ! the genernal expression for water flow is "K * ss**3", however, ! no effective parameterization for "K".  Thus, a very simple consideration ! (not physically based) is introduced: ! when the liquid water of layer exceeds the layer's holding ! capacity, the excess meltwater adds to the underlying neighbor layer.!          qin = 0.     do j= clm%snl+1, 0        clm%h2osoi_liq(j) = clm%h2osoi_liq(j) + qin        if (j <= -1) then           ! No runoff over snow surface, just ponding on surface           if (eff_porosity(j)<clm%wimp .OR. eff_porosity(j+1)<clm%wimp) then              qout = 0.           else              qout = max(0._r8,(vol_liq(j)-clm%ssi*eff_porosity(j))*clm%dz(j))              qout = min(qout,(1.-vol_ice(j+1)-vol_liq(j+1))*clm%dz(j+1))           endif        else           qout = max(0._r8,(vol_liq(j)-clm%ssi*eff_porosity(j))*clm%dz(j))        endif        qout = qout*1000.        clm%h2osoi_liq(j) = clm%h2osoi_liq(j) - qout        qin = qout     enddo          qout_snowb = qout/clm%dtime     clm%qflx_top_soil = qout_snowb       endifend subroutine SnowWater