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net.simplace.sim.components.soil.temperature.SnowCoverCalculator

Calculates the snow cover, first soil layer temperature and biomass on ground factor depending on climate and soil conditions.

Snow Cover

Snow Cover is calculated using the formula:

\[ \begin{eqnarray} DST0=(1.-BCV) \cdot DST + BCV \cdot STMP0 \end{eqnarray} \]

Snow Cover calculation

If the soil surface is not bare, the surface temperature can be affected considerably by the amount of cover (crop residue or snow). This effect can be simulated by combining the estimated bare surface temperature for the day with the previous day's temperature in the second soil layer (the top 10 mm layer is considered too thin for this purpose).

where DST0 is the final estimate of soil surface temperature in °C and BCV is a lagging factor for simulating residue and snow cover effects on surface temperature. The value of BCV is 0.0 for bare soil and approaches 1.0 as cover increases, as expressed in the equation

\[ \begin{eqnarray} BCV &=& max(SNOF,BCV') \\ BCV' &=& \frac{CV}{CV+exp(5.34-2.40 \cdot CV)} \\ SNOF &=& \frac{SNO}{SNO+exp(2.30-0.220 \cdot SNO)} \end{eqnarray} \]

where

CV is the sum of above ground biomass and crop residue in t ha-1 and
SNO is the water content of the snow cover in mm.

Snow melt

If snow is present, it may be melted on days when the second soil layer temperature exceeds 0 oC. Snow is melted as a function of the snow pack temperature using the equation

\[ \begin{eqnarray} SML &=& max(0.,X1 \cdot (1.52+.54 \cdot F \cdot SNPKT)) \quad \text{for} \quad 0.0 \lt SML \lt SNO \\ SNPKT & =& .3333 \cdot (2. \cdot X2+TX) \\ X1 &=& \sqrt{TMX \cdot RA} \\ X2 &=& min(DST0,STMP(2)) \\ F &=& TSNO/(TSNO+exp(5.34-2.395 \cdot TSNO)) \end{eqnarray} \]

where

SML is the snowmelt rate in mm d-1,
SNO is the snow present in mm of water,
STMP is the temperature in oC of soil layer 2,
SNPKT is the snow pack temperature in oC,
DST0 is the soil surface temperature in oC, and
TSNO is the age of the snow pack in d.

The equations for estimating STMP and DST0 are presented in the soil temperature section. Melted snow is treated the same as rainfall for estimating runoff volume and percolation, but rainfall energy is set to 0.0 and peak runoff rate is estimated by assuming uniformly distributed rainfall for a 24-h duration.

Snow evaporation

EAJ is a soil cover index. The value of EAJ ranges from 0 to 1.0 according to the equation

\[ \begin{eqnarray} EAJ & = & exp(-X1) \\ X1 & = & max(0.4 \cdot SMLA,0.1 \cdot (CV+.1)) \end{eqnarray} \]

where

CV is the weight of all above ground plant material in t ha-1.

Reference:

Williams, J.R., Izaurralde, C.A., 2005. The APEX model, Blackland Research Center Reports, Vol. 2. Blackland Research Center, USDA, Temple, Texas, USA

Component Variables

Content Type	Name	Description	Data Type	Unit	Min Value	Max Value	Default Value
constant	cCarbonContent	Carbon content of upper soil layer	DOUBLE	%	0.0	20.0	0.5
input	iCropResidues	Crop residues plus above ground biomass	DOUBLE	g/m2	0.0	20000.0	-
input	iDoInitialize	Switch to re-initialize the model with initial values.	BOOLEAN	1	-	-	false
input	iLeafAreaIndex	Leaf area index	DOUBLE	m2/m2	0.0	10.0	-
input	iPotentialSoilEvaporation	Potenial Evaporation	DOUBLE	mm	0.0	12.0	-
input	iRAIN	Rain amount	DOUBLE	mm	0.0	60.0	-
input	iRadiation	Solar radiation	DOUBLE	MJ/m2	0.0	2000.0	-
input	iSoilTempArray	Soil Temp array of last day	DOUBLEARRAY	°C	-15.0	35.0	-
input	iTempMax	Daily maximum temperature	DOUBLE	°C	-40.0	50.0	-
input	iTempMin	Daily minimum temperature	DOUBLE	°C	-40.0	50.0	-
out	AgeOfSnow	Age of snow	INT	1	0	-	0
out	Albedo	Albedo	DOUBLEARRAY	1	0.0	1.0	-
out	SnowIsolationIndex	Snow isolation index	DOUBLE	1	0.0	1.0	0.0
out	SnowWaterContent	Snow water content	DOUBLE	mm	0.0	1500.0	0.0
out	SoilSurfaceTemperature	Soil surface temperature	DOUBLE	°C	-40.0	70.0	0.0

public class SnowCoverCalculator extends net.simplace.sim.model.FWSimComponent {
// Public Constructors
public SnowCoverCalculator();

// Public Instance Methods

public HashMap createVariables(); // Defines
net.simplace.sim.model.FWSimComponent

create the FWSimVariables as interface for this SimComponent

// Protected Instance Methods

protected void init(); // Defines net.simplace.sim.model.FWSimComponent

initializes the fields by getting input and output FWSimVariables from VarMap

protected void reInitialize();

protected void process(); // Defines net.simplace.sim.model.FWSimComponent

process the algorithm and write the results back to VarMap

protected FWSimComponent clone(FWSimVarMap aVarMap);
// Defines net.simplace.sim.model.FWSimComponent

creates a clone from this SimComponent for use in other threads

}

Hierarchy: java.lang.Object - net.simplace.sim.model.FWSimComponent (net.simplace.sim.util.FWSimFieldContainer) - SnowCoverCalculator