waterUnderCanopy.f90 File Reference

Assesses water flux elements at the ground surface under the vegetation canopy. More...

Functions/Subroutines
subroutine	waterundercanopy (IWATER, R, TR, S, TS, RHOSNI, EVAPG, QFN, QFG, PCPN, PCPG, FI, ILG, IL1, IL2, JL)

Detailed Description

Assesses water flux elements at the ground surface under the vegetation canopy.

Author

D. Verseghy, M. Lazare

Function/Subroutine Documentation

waterundercanopy()

subroutine waterundercanopy	(	integer, intent(in)	IWATER,
		real, dimension (ilg), intent(inout)	R,
		real, dimension (ilg), intent(out)	TR,
		real, dimension (ilg), intent(inout)	S,
		real, dimension (ilg), intent(out)	TS,
		real, dimension(ilg), intent(in)	RHOSNI,
		real, dimension (ilg), intent(inout)	EVAPG,
		real, dimension (ilg), intent(inout)	QFN,
		real, dimension (ilg), intent(inout)	QFG,
		real, dimension (ilg), intent(inout)	PCPN,
		real, dimension (ilg), intent(inout)	PCPG,
		real, dimension (ilg), intent(in)	FI,
		integer, intent(in)	ILG,
		integer, intent(in)	IL1,
		integer, intent(in)	IL2,
		integer, intent(in)	JL
	)

Parameters

[in,out]	r	Rainfall rate incident on ground \([m s^{-1}]\)
[in,out]	s	Snowfall rate incident on ground \([m s^{-1}]\)
[out]	tr	Temperature of rainfall [C]
[out]	ts	Temperature of snowfall [C]
[in,out]	evapg	Evaporation rate from surface \([m s^{-1}]\)
[in,out]	qfn	Sublimation from snow pack \([kg m^{-2} s^{-1}]\)
[in,out]	qfg	Evaporation from ground \([kg m^{-2} s^{-1}]\)
[in,out]	pcpn	Precipitation incident on ground \([kg m^{-2} s^{-1}]\)
[in,out]	pcpg	Precipitation incident on ground \([kg m^{-2} s^{-1}]\)
[in]	rhosni	Density of fresh snow \([kg m^{-3}]\)
[in]	fi	Fractional coverage of subarea in question on modelled area [ ]

This subroutine starts with the precipitation rate under the canopy (a result of throughfall and unloading) and calculates the resulting overall evaporation or deposition rates.

For IWATER = 2 (snow on the ground under the canopy), the water vapour flux EVAPG at the ground surface is in the first instance assumed to be sublimation. Thus the first step is to compare it to the snowfall rate. The sum of the snowfall rate and the evaporation rate, SADD, is calculated as S – EVAPG, with EVAPG converted from a liquid water flux (the standard output from energBalVegSolve) to a snow flux. If SADD is greater than zero (indicating a downward flux) the snowfall rate is set to SADD and EVAPG is set to zero. Otherwise EVAPG is set to -SADD (converted back to a liquid water flux), and S and TS are set to zero.

After this section, any remaining evaporative flux is compared to the rainfall rate. The sum RADD is calculated as R – EVAPG. If RADD is greater than zero, the rainfall rate is set to RADD and EVAPG is set to zero. Otherwise EVAPG is set to –RADD, and R and TR are set to zero.

Analogous calculations are done for IWATER = 1 (bare ground under the canopy). In this case EVAPG is assumed in the first instance to be evaporation or condensation. Thus the first step is to compare it to the rainfall rate, and the same steps are followed as in the paragraph above. Afterwards, any remaining vapour flux is compared to the snowfall rate. If SADD is positive (downward), EVAPG, which is now considered to be absorbed into the snowfall rate, is subtracted from the ground vapour flux QFG and added to the snow vapour flux QFN. If SADD is negative (upward), S, which has now been absorbed into the evaporative flux, is subtracted from the snow precipitation flux PCPN and added to the ground precipitation flux PCPG.