October 7, 2015
Parameters and input data are in bold. Some variables end in P for precipitation interval, D for day, M for month, and Y for year.
AA - average available energy over daytime or nighttime, W/m2. [see SUN-AVAILEN]
ADEF - available water deficit in root zone, mm, output variable.
ALB and ALBSN (Canopy parameters) - albedo or surface reflectivity without and with snow on the ground, respectively. Used to calculate net radiation from solar radiation [see SUN-AVAILEN]. Except for choosing which of these two values to use, albedo does not vary with time in BROOK90. ALB generally ranges from 0.1 for bare soil and water to 0.3 for some vegetation. ALBSN ranges from 0.1 for some forests to 0.9 for bare fresh snow. In BROOK90 ALBSN only affects interception and transpiration, not snow evaporation and snow energy balance. [see SUN-AVAILEN]
ALBEDO - albedo, equal to ALB when no snow or ALBSN when SNOW exists. [see SUN-AVAILEN]
ALBSN - see ALB
ALPHA(1 To ML) - modified Cowan alpha, MPa. [see EVP-PLNTRES] [see EVP-TBYLAYER]
ASPECT and ASPECTD (Location parameter) - aspect, degrees through east from north. Used in radiation calculations. In code ASPECTD is in degrees, ASPECT is in radians. If ESLOPE = 0, ASPECT is ignored. [see SUN-EQIVSLP]
ASUBS - average available energy at ground over day or night, W/m2. [see SUN-AVAILEN]
ATR(2) - actual transpiration rate for daytime
or night, mm/d.
ATRANI(1 To ML) - actual transp.rate from layer for daytime or night,mm/d.
ATRI(2, 1 To ML) - actual transp.rate from layer for daytime and night,mm/d.
AWAT - total available soil water in layers with roots, between PSIF and PSICR, mm, output only. When there are no roots, e.g. when RELHT = 0, AWAT = 0. [see KPT-SOILPAR]
BALERD, BALERM, BALERY - error in water balance. mm.
BEXP(1 To ML) (Soil parameter) - exponent for ψ-θ relation. BEXP is the negative slope of the log ψ - log θ relationship, or the exponent in the Brooks and Corey equation as given by Clapp and Hornberger (1978). This parameter is usually b in the literature. Values of BEXP above 11.5 will not work unless WETINF is set higher than 0.92. [see KPT]
BYFL - bypass flow rate from all layers for
iteration, mm/d. To eliminate BYFL, set BYPAR = 0.
[see WAT-BYFLFR]
[see WAT-INFLOW]
BYFLI(1 To ML) - bypass flow rate from layer, mm/d.
BYFLPI(1 To ML), BYFLDI(1 To ML), BYFLMI(1 To ML), BYFLYI(1 To ML) - bypass
flow from layer, mm.
BYFLP, BYFLD, BYFLM, BYFLY - total bypass flow, mm.
BYFRAC(1 To ML) - fraction of layer infiltration going to bypass flow. [see WAT-BYFLFR] [see WAT-INFLOW]
BYPAR (Flow parameter) - either 0 to prevent bypass flow (BYFL), or 1 to allow BYFL . BYFL is zero when BYPAR = 0, unless the surface layer becomes saturated. When BYPAR = 1, a fraction of infiltration to each layer is immediately routed to bypass flow to simulate downslope macropore or pipe flow of new water. The fraction depends on QFFC and QFPAR. These are the same parameters used to determine source area flow (SRFL), so simulation with both SRFL and BYFL (QDEPTH > 0 and BYPAR = 1) is discouraged. The difference is that SRFL depends on the total water content down to QDEPTH whereas BYFL depends on water content in each layer down to IDEPTH. When NLAYER = 1, SRFL and BYFL are identical. [see WAT-BYFLFR]
C1 and C2 (Fixed parameters) - intercept and slope of linear relation between the ratio of actual to potential solar radiation for the day and sunshine duration. C1 is fixed at 0.25 and C2 at 0.5 following Brutsaert (1982). [see SUN-AVAILEN]
C3 (Fixed parameter) - ratio of net longwave radiation for overcast sky (sunshine duration = 0) to that for clear sky (sunshine duration = 1). C3 is fixed at 0.2 following Brutsaert (1982). [see SUN-AVAILEN]
CC - cold content of snowpack (positive), MJ m-2. [see SNO-SNOWPACK]
CCFAC (Fixed parameter) - cold content factor, MJ m-2 d-1 K-1. CCFAC is a degree day factor for accumulation of cold content for a day with daylength of 0.5 d. It controls the snow energy balance when TA is less than 0°C. Larger values make the snow temperature lag farther behind the air temperature. Sensitivity of snowmelt to CCFAC is small unless CCFAC is less than 0.05 MJ m-2 d-1 K-1. CCFAC = 0 means there is no cold content and snow temperature is always 0°C. CCFAC is fixed at 0.3 MJ m-2 d-1 K-1. [see SNO-SNOENRGY]
CHM(1 To ML) - m value in
Clapp and Hornberger (1978)
relation of soil water potential to soil water content, kPa.
[see KPT]
CHN(1 To ML) - n value in Clapp and Hornberger (1978) relation of soil water
potential to soil water content.
CINTRL and CINTRS (Fixed parameters) - maximum interception storage of rain per unit LAI and SAI, respectively, mm. This storage is only removed by evaporation, so does not include water that drips off. CINTRL and CINTRS are both fixed at 0.15 mm. Studies of rain interception in mature forests generally indicate a capacity of 1 or 2 mm. With CINTRL and CINTRS set at 0.15, an LAI of 6 and an SAI of 0.7 gives a capacity of 1.0 mm. LAI is on a projected area basis, so the assumption is that only the projected area is wetted. [see EVP-INTER]
CINTSL and CINTSS (Fixed parameters) - maximum interception storage of snow water per unit LAI and SAI, respectively, mm. This storage is only removed by evaporation, so does not include water that drips or falls off. CINTSL and CINTSS are both fixed at 0.6. With LAI = 6 and SAI = 0.7, maximum snow water interception capacity is 4.0 mm corresponding to the value used by Federer and Lash (1978b). This capacity is slightly lower than the 5 and 7.5 mm that Leaf and Brink (1973) used for lodgepole pine and spruce-fir, but BROOK90 assumes that all of this will evaporate while they do not. When LAI = 0 and SAI = 0.7 the capacity is 0.4 mm. LAI is on a projected area basis, so the assumption is that only the projected area is wetted. [see EVP-INTER]
CPRHO - volumetric heat capacity of air, cpρ , constant at 1240 J m-3 K-1) Actually ρ varies slightly with air temperature, air humidity, and atmospheric pressure, but this variation is ignored in BROOK90. [see PET-PM] [see SNO-SNOVAP]
CR (Canopy parameter) - extinction coefficient for photosynthetically-active radiation in the canopy. Values usually range from 0.5 to 0.7. Values outside this range should be used very cautiously. The extinction coefficient can be determined from the canopy transmissivity, t, as CR = - (ln t) / (Lp + Sp). For a canopy of Lp = 6 and Sp = 0.7, PAR penetration at the ground of 1, 3, and 5% gives CR = 0.69, 0.52, and 0.45 respectively. I use CR values of 0.5 for conifer forest, 0.6 for broadleaved forest, and 0.7 for short vegetation covers. CR is also used to calculate the extinction of net radiation, though this is theoretically incorrect. [see PET-SRSC] [see SUN-AVAILEN]
CS (Canopy parameter) - ratio of projected stem area index (SAI) to HEIGHT when DENSEF = 1. SAI = CS * HEIGHT * DENSEF. For a total stem area index of closed canopy forests of roughly 2 for a 20 m height (Federer and Lash 1978), and cylindrical "stems" then CS is 2 / (20 π) or 0.035. A high value of CS and a small MAXHT might be used to simulate logging slash in a clearcut. If DENSEF is not reduced, CS should be reduced for a sparse canopy. [see PET-CANOPY]
CVICE - constant volumetric heat capacity of ice, 0.00192 MJ m-2 mm-1 K-1. [see SNO-SNOWPACK]
CVLQ - constant volumetric heat capacity of water, 0.00418 MJ m-2 mm-1 K-1 . [see SNO-SNOWPACK]
CVPD (Fixed parameter) - vapor pressure deficit at which stomatal conductance is halved, kPa. Values of cD between 0.5 and 2 kPa are generally found in the literature. In BROOK90 CVPD is fixed at 2 kPa for all cover types. A very large value will remove vapor pressure dependence. Values less than 1 kPa produce too much sensitivity. After GLMAX, this parameter probably has the next largest effect on potential transpiration. Unfortunately there is very little data on how it varies among species (Körner 1994). [see PET-SRSC]
CZR, HR, CZS, and HS (Fixed parameters) - CZR is the ratio of roughness parameter to HEIGHT when HEIGHT is greater than HR and canopy is closed (LAI > LPC). CZS is the ratio of roughness parameter to HEIGHT when HEIGHT is less than HS and canopy is closed. For heights between HS and HR, the roughness parameter is interpolated. CZR is fixed at 0.05 and HR is fixed at 10 m. CZS is fixed at 0.13 and HS is fixed at 1 m. [see PET-ROUGH]
DAYLEN - daylength in fraction of day, d-1. [see SUN-SUNDS] [see PET-WEATHER] [see SNO-SNOENRGY]
DAYMO(12) - days in month, constant corrected for leap years.
DD (input variable) - day of the month.
DELTA - rate of change of saturated vapor pressure with temperature at specified temperature, kPa/K. [see PET-PM]
DENSEF (Fixed parameter) - canopy density multiplier between 0.05 and 1, dimensionless. DENSEF is normally 1; it should be reduced below this ONLY to simulate thinning of the existing canopy by cutting. It multiplies MAXLAI, CS, MXRTLN, and MXKPL and thus proportionally reduces LAI, SAI, and RTLEN, and increases RPLANT. However it does NOT reduce canopy HEIGHT and thus will give erroneous aerodynamic resistances if it is less than about 0.05. It should NOT be set to 0 to simulate a clearcut. [see PET-CANOPY]
DISP - zero-plane displacement, m. [see PET-ROUGH] [see PET-WNDADJ] [see EVP-TBYLAYER]
DISPC - zero-plane displacement for closed canopy of HEIGHT, m. [see PET-ROUGH] [see EVP-PLNTRES]
DOY - day of the year. This value, which ranges from 1 to 365 in regular years or 366 in leap years, is often erroneously called "Julian day". The Julian day is actually the number of 24 hour periods that have elapsed since noon Greenwich Mean Time on January 1, 4713 B.C. (see any dictionary, or Stone 1983). January 1, 1992 after noon GMT is Julian day 2,448,622.
DPSIDW(1 To ML) - rate of change of total potential with water content,kPa/mm.
DPSIMX (Fixed parameter) - maximum potential difference considered equal during soil water integration, kPa. There is no vertical flow between layers whose potentials differ by less than DPSIMX. This reduces oscillation initiated by flows that are the product of large conductivities and large time steps, but small gradients. The number of iterations used is not at all linearly related to the three iteration parameters DPSIMX, DSWMAX, and DTIMAX. Selection of values depends on whether the user only wants monthly or daily totals, or is concerned with behaviour at shorter time steps. Generally, faster runs are obtained by using fewer thicker soil layers rather than by using large values of DSWMAX and DPSIMX. DPSIMX is fixed at 0.01 kPa. [see WAT-ITER]
DRAIN (Flow parameter) - multiplier between 0 and 1 of drainage from the lowest soil layer, VRFLI(n), for drainage to groundwater, dimensionless. DRAIN = 1 produces vertical drainage under gravity gradient. DRAIN = 0 prevents drainage from the bottom of the soil column. Values between 0 and 1 can also be used, especially to control DSFL. [see WAT-VERT] [see WAT-DSLOP]
DSFL - downslope flow rate from all layers for
iteration, mm/d. To eliminate DSFL set DSLOPE to zero.
[see WAT-DSLOP]
[see WAT-INFLOW]
DSFLI(1 To ML) - downslope flow rate from layer, mm/d.
DSFLP, DSFLD, DSFLM, DSFLY - downslope flow, mm.
DSFLPI(1 To ML), DSFLDI(1 To ML), DSFLMI(1 To ML), DSFLYI(1 To ML) - -
downslope drainage from layer, mm.
DSLOPE and DSLOPED (Flow parameter) - hillslope angle for downslope matric flow (DSFL), degrees. In code DSLOPED is in degrees, DSLOPE is in radians. Because downslope flow is overparameterized, arbitrarily setting DSLOPE to 10° is satisfactory for DSFL from the bottom soil layer(s). When either DSLOPE or LENGTH is 0 there is no DSFL, and the other parameter is ignored. [see WAT-DSLOP]
DSWMAX (Fixed parameter) - maximum change allowed in soil wetness for any layer during an iteration, percent. DSWMAX sets the maximum change in soil wetness or saturation fraction (SWATI / SWATMX(i)) allowed for any layer in an iteration. See also DPSIMX. DSWMAX is fixed at 2 %. [see WAT-ITER]
DT - constant time step for input data file interval and basic model time step, 1.0 d.
DTI and DTINEW - time step for iteration interval and its second estimate - d. [see WAT-INFLOW] [see WAT-ITER] [see WAT-GWATER]
DTIMAX (Fixed parameter) - maximum iteration time step, d. DTIMAX is fixed at 0.5 d, which forces at least two iterations per day. This is the largest value that should be used. Much smaller values of DTIMAX, between 0.01 and 0.001 d, will force many iterations per day and thus smooth integration. However, a run with such a small DTIMAX takes a long time. See also DPSIMX. [see WAT-ITER]
DTP - time step for precipitation interval, may be <= 1 d, calculated parameter [see SNO-SNOWPACK]
DTRI - time remaining in precipitation interval, d.
DUMM() - dummy array for subroutine calls.
DURATN(1 To 12) (Location parameter) - average duration of daily precipitation by month, hr. When a precipitation input file is not used, DURATN is used in subroutine INTER24 to estimate interception processes hourly. It is the average number of hours per day with precipitation. Do not use a DURATN of 1, or no interception will be produced. Fractional values are truncated to the next lower even integer. Provision of 12 monthly values for DURATN allows seasonal variation of storm type from low intensity, long DURATN, to high intensity, short DURATN. In reality, though, this seasonal difference is not large. The number of hours a day that precipitation exceeds 0.5 mm varies only from 2 to 6 for most seasons and locations in the United States (see EVP-INTER24. DURATN = 4 for all months is a satisfactory approximation. DURATN is ignored when a precipitation interval file is provided; then precipitation is assumed constant over the precipitation interval, and subroutine INTER is used. [see EVP-INTER24]
EA (Input variable) - vapor pressure for the day, kPa. If input EA is zero, EA is set to the saturated vapor pressure at TMIN. [see PET-WEATHER] [see SUN-AVAILEN] [see PET-PM] [see SNO-SNOVAP]
ES - saturated vapor pressure at air temperature, ea* , kPa. [see PET-PM]
ESLOPE and ESLOPED (Location parameter) - slope for evapotranspiration and snowmelt, degrees. In code ESLOPED is in degrees, ESLOPE is in radians. ESLOPE is used for net radiation and snowmelt. See also DSLOPE. [see SUN-EQUIVSLP]
ETOM - 1 / ( Lv ρw) = 0.4085(mm water)/(MJ/m2) where Lv is the latent heat of vaporization (2448 MJ/Mg) and ρw is the density of water (1 Mg/m3) latent heat flux (energy) to vapor flux (mass) conversion. Actually, Lv varies with temperature, but this variation is small compared to other uncertainties. See also WTOMJ. [see PET-PM]
EVAPP, EVAPD, EVAPM, EVAPY - evapotranspiration, mm.
FARR(1 To 366) - array of simulated daily flow for statistics.
FETCH (Fixed parameter) - fetch upwind of the weather station at which wind speed was measured, m. Sensitivity to FETCH is small if it is > 1000 m. See also Z0W. FETCH is fixed at 5000 m. FETCH is ignored if Z0W = 0. [see PET-WNDADJ]
FLOWP, FLOWD, FLOWM, FLOWY - total streamflow, mm.
FRINTL and FRINTS (Fixed parameters) - intercepted fraction of rain per unit LAI and per unit SAI respectively, dimensionless. See also FSINTL. FRINTL and FRINTS are both fixed at 0.06. For LAI = 6 and SAI = 0.7 these values give a rain catch rate of 40% of the rainfall rate. For leafless deciduous forest with LAI = 0 and SAI = 0.7 the rain catch rate is 4%. To turn off RINT, set both FRINTL and FRINTS to zero. [see EVP-INTER]
FSINTL and FSINTS (Fixed parameters) - intercepted fraction of snow per unit LAI and per unit SAI respectively, dimensionless. See also FRINTL. FSINTL and FSINTS are both fixed at 0.04. For LAI = 6 and SAI = 0.7 these values catch snow at 27%. For leafless deciduous forest with LAI = 0 and SAI = 0.7 the snowfall catch rate is 3%. To turn off SINT, set both FSINTL and FSINTS to zero. [see EVP-INTER]
FXYLEM (Canopy parameter) - fraction of plant resistance that is in the xylem. FXYLEM is the fraction of the internal plant resistance to water flow that is in the xylem, which is considered to be all above ground.The remaining resistance is considered to be in the root cortex and is therefore distributed among soil layers containing roots. Increasing FXYLEM reduces the dependence of layer uptake on root density in the layer and thus makes transpiration uptake more uniform with depth. FXYLEM probably should be zero for short canopies and increase linearly with height to 0.5 for forests of MAXHT = 25 m (Hunt et al. 1991). It can vary from 0 to 1. When FXYLEM = 1 it is reset to 0.99. [see EVP-PLNTRES]
GAMMA - psychrometer constant, 0.067 kPa/K. Actually γ varies slightly but this variation is ignored in BROOK90. [see PET-PM] [see SNO-SNOVAP]
GER(2) - ground evaporation rate for daytime or
night, mm/d.
[see PET]
GEVP - average ground evaporation for day, mm/d.
GIR(2) - ground evap. rate with intercep. for daytime or night,mm/d.
[see PET]
GIVP - average ground evaporation for day with interception, mm/d.
GLMAX and GLMAXC (Canopy parameter) - maximum leaf conductance, cm/s. In code GLMAX is in m/s and GLMAXC is in cm/s. GLMAX is the maximum leaf conductance when stomates are fully open.It is the total conductance of all sides of a leaf or needle, based on projected leaf area. This is an important parameter controlling potential transpiration. Values for all plant types should be in the range 0.2 to 2.0 cm/s. [see PET-SRSC]. This conductance is reduced by low light, low or high temperature, and high vapor pressure deficit in calculating canopy resistance (RSC) and thus potential transpiration (PTRAN). Values by cover type in the b90v44data.zip Canopy parameter files are from Körner (1994). He concluded that GLMAX does not vary among forest types, even though it differs among individual species. Guidance in selecting GLMAX for specific species can be found in Hinckley et al. (1978) and Körner (1979), or this can be a fitting parameter to give appropriate transpiration. [see PET-SRSC]
GLMIN and GLMINC (Canopy parameter) - minimum leaf conductance, cm/s. In code, GLMIN is in m/s and GLMINC is in cm/s. GLMIN is the average nighttime leaf conductance, or the conductance when stomates are closed. This value is used for the whole day when mean daily temperature is below TL or above TH. If GLMIN is set to 0 a value of 0.00001 is used to avoid possible zero divide. GLMIN is fixed at 0.0003 m/s. [see PET-SRSC]
GRDMLT (Fixed parameter) - rate of groundmelt of snowpack, mm/d. GRDMLT is the constant rate of melt at the bottom of the snowpack because of soil heat transfer to the snow. This parameter controls low flow during winter periods with snowpack. BROOK90 assumes that there is never any soil frost. GRDMLT is fixed at 0.35 mm/d from Hubbard Brook (Federer 1965). [see SNO-SNOWPACK]
GSC (Flow parameter) - fraction of groundwater storage (GWAT), that is transferred to groundwater flow (GWFL) and deep seepage (SEEP) each day, d-1. Where groundwater is being simulated, GSC should be some fraction like 0.1 d-1 or less. If GSC = 0 there is no groundwater storage and all vertical drainage from the soil profile becomes seepage or streamflow directly. See also GSP. [see WAT-GWATER]
GSP (Flow parameter) - fraction of groundwater discharge produced by GSC that goes to deep seepage (SEEP) and is not added to streamflow (FLOW), dimensionless. If GSC = 0, GSP applies to vertical drainage from the bottom soil layer. To eliminate SEEP set GSP to zero. [see WAT-GWATER]
GTRANS - constant ratio of SOLRAD to I0HDAY used to estimate SOLRAD when it is input as 0, 0.55. Obsolete as of Version 4.8. [see SUN]
GWAT and GWATIN (Initial value) - groundwater storage below soil layers, mm. In code GWATIN is the initial value. Initial value effects can last for days to months. A value of 0 can always be used, but there will be initially low GWFL if GSC is small. Ideally the first year of a run should be discarded so the initial value becomes irrelevant. To eliminate GWAT storage completely set both GWATIN and GSC to zero. [see WAT-GWATER]
GWFL - rate from groundwater flow to streamflow
(FLOW), mm/d.
[see WAT-GWATER]
GWFLP, GWFLD, GWFLM, GWFLY - groundwater flow, mm.
HEIGHT - canopy height, m. HEIGHT = RELHT * MAXHT - SNODEP. [see PET-CANOPY]
HIBL - height of the boundary layer, m. Local to subroutine WNDADJ.
HR and HS - see CZR.
I - index variable for layer number
I0HDAY - potential insolation on horizontal, MJ m-2 d-1. [see SUN-SUNDS]
IDAY - day number in run, including initialize days.
IDEPTH (Flow parameter) - depth over which infiltration is distributed, mm. IDEPTH determines the number of soil layers over which infiltration is distributed when INFEXP is greater than 0. It should correspond to the depth of vertical macropores. IDEPTH does not need to correspond to the bottom of a soil layer; it is converted into the number of soil layers most closely corresponding to IDEPTH. [see WAT-INFPAR].
II - input precipitation interval number, input variable.
IMPERV (Flow parameter) - fraction of the soil surface that is impermeable and always routes water reaching it directly to streamflow as SRFL. For a watershed, IMPERV represents at least the area of the stream channel; an appropriate value is 0.01. To turn off SLFL set IMPERV = 1. To turn off SRFL set both IMPERV and QDEPTH to zero. [see WAT-SRFLFR]
INFEXP (Flow parameter) - infiltration exponent that determines the distribution of infiltrated water with depth, dimensionless. When INFEXP = 0, all infiltration goes to the top soil layer and a classic top-down wetting front is produced. Increasing INFEXP corresponds to increasing macropore-assisted infiltration, and produces an exponential depth distribution of infiltrated water down through the layer whose lower depth most closely corresponds to IDEPTH. With INFEXP = 1, infiltrated water is distributed uniformly down to the IDEPTH layer. Values above 1 put more water into lower layers than into upper layers. [see WAT-INFPAR] [see WAT-BYFLFR]
INFRAC(1 To ML) - fraction of infiltration to each layer, calculated parameter. [see WAT-INFPAR] [see WAT-INFLOW]
INFLI(1 To ML) - infiltration rate into layer,
mm/d. To eliminate INFL to all layers except the top layer set
INFEXP to zero.
[see WAT-INFLOW]
INFLP, INFLD, INFLM, INFLY - total infiltration into soil water, mm.
INFLPI(1 To ML), INFLDI(1 To ML), INFLMI(1 To ML), INFLYI(1 To ML) -
infiltration to soil water in layer, mm.
INTR, INTS, INTRIN, and INTSIN (Initial values) - intercepted rain and snow, mm. In code INTRIN and INTRS are the initial values. Initial value effects last only one to several days. [see EVP-INTER].
IRVP - evaporation rate of intercepted rain, mm/d.
[see EVP-INTER]
IRVPD, IRVPM, IRVPY - evaporation of intercepted rain, mm.
ISVP - evaporation rate of intercepted snow, mm/d.
[see EVP-INTER]
ISVPD, ISVPM, ISVPY - evaporation of intercepted snow, mm.
J - index variable for day-night separation, 1 for day, 2 for night.
KF(1 To ML) (Soil parameter) - hydraulic conductivity at field capacity corresponding to THETAF and PSIF for a soil layer, mm/d. KF replaces the more usual but conceptually questionable value of saturated hydraulic conductivity. The concept of field capacity is not used for matric flow of soil water, but is used to calculate SLVP, SRFL, BYFL, and ADEF. [see KPT for much more on KF]
KK(1 To ML) - hydraulic conductivity, mm/d. [see KPT] [see EVP-TBYLAYER] [see WAT-VERT] [see WAT-DSLOP]
KSAT(1 To ML) - saturated hydraulic conductivity, mm/d, calculated parameter. [see KPT-SOILPAR]
KSNVP (Canopy parameter) - reduction factor between 0.05 and 1 to reduce snow evaporation (SNVP), dimensionless. It is needed for tall canopies because the Shuttleworth-Gurney aerodynamic resistances as corrected for SAI are too low and thus overestimate SNVP from forests. Set KSNVP to 1 for short canopies, and in the absence of better information, use 0.3 for tall forest and intermediate values for intermediate heights. To turn off SNVP set KSNVP to zero. [see SNO-SNOVAP]
L1 and L2 - latitude of equivalent slope, radians, and time shift of equivalent slope, radians, calculated parameters. [see SUN-EQUIVSLP]
LAI - projected leaf area index, m2/m2. LAI is defined as the area of leaves above a unit ground area, when the area of a leaf or needle is defined by the projection of the flattened leaf onto a plane through its longest and widest dimensions. LAI = MAXLAI * RELLAI(DOY) * DENSEF * RATIO where MAXLAI is the maximum value and RELLAI, DENSEF, and RATIO account for phenology, plant thinning, and burial by snow, respectively. [see SUN-AVAILEN] [see PET-SWGRA] [see EVP-INTER] [see SNO-SNOENRGY]
LAIMLT (Fixed parameter) - dependence of snowmelt on LAI, dimensionless. Melt is linearly proportional to exp(-LAIMLT * LAI) so melt decreases exponentially as LAI increases. LAIMLT is fixed at 0.2. This value makes the exp factor 1.0, 0.67, 0.45, and 0.30 for LAI = 0, 2, 4, and 6 respectively. [see SNO-SNOENRGY]
LAT and LATD (Location parameter) - latitude, degrees. In code, LATD is in degrees and LAT in radians. LAT is the location latitude in degrees north for solar radiation calculations Negative values are used in the southern hemisphere. This is the only parameter that is specific to geographic location. [see SUN-EQUIVSLP]
LENGTH (Flow parameter) - slope length for downslope flow (DSFL), m. LENGTH is conceptually the hillslope length in m as horizontal or map distance from ridge to channel. But in practice it is a fitted value to produce the desired amount of DSFL, which is roughly inversely proportional to LENGTH. Downslope flow from the bottom soil layer(s) is overparameterized, so LENGTH can be set to 10 m and DSFL can be varied by changing DRAIN. When either DSLOPE or LENGTH are 0 there is no downslope flow, and the other parameter is ignored. [see WAT-DSLOP]
LF - constant heat of fusion of water, 0.335 MJ m-2 mm-1 . [see SNO-SNOWPACK]
LPC (Fixed parameter) - minimum LAI defining a closed canopy, dimensionless. LPC is the projected leaf area index above which the canopy is considered closed in the Shuttleworth and Wallace (1985) equations. LPC is fixed at 4.0. [see PET-ROUGH]
LS - constant latent heat of sublimation of snow, 2.824 MJ m-2 mm-1 . [see SNO-SNOVAP]
LWIDTH (Canopy parameter) - average leaf width, m. LWIDTH is the average leaf width (generally its second smallest dimension) used to determine the leaf boundary resistance RAC. [see PET-SWGRA]
MARR(1 To 366) - array of measured daily flow for statistics.
MAXHT (Canopy parameter) - maximum canopy height for the year, m. MAXHT is the maximum height for the year as an average height of the taller plants. Actual canopy height is HEIGHT = MAXHT * RELHT (DOY) - SNODEP, which can vary throughout the year. HEIGHT is prevented from being less than 0.01 m. [see PET-CANOPY]
MAXLAI (Canopy parameter) - maximum projected LAI for the year, m2/m2. Many closed canopies have MAXLAI about 6. LAI is prevented from being less than 0.00001 to avoid zero divides. [see PET-CANOPY]
MAXLQF (Fixed parameter) - maximum liquid water fraction of SNOW, dimensionless. MAXLQF is the liquid water fraction of the snow water, SNOW, at which water drains. MAXLQF is fixed at 0.05, which is appropriate in most snow environments. [see SNO-SNOWPACK]
MELFAC (Location parameter) - degree day melt factor for open land, MJ m-2 d-1 K-1. MELFAC is the degree-day snowmelt factor for a day with daylength of 0.5 d and no plant canopy. Dividing MELFAC by the heat of fusion of water, LF (= 0.335 MJ m-2 mm-1), gives the more usual degree day factor in mm d-1 K-1. MELFAC = 1.5 MJ m-2 d-1 K-1, or 4.5 mm d-1 K-1, is a good starting value; it is in the lower end of the range given by Federer et al. (1973) and is close to the 4.2 mm d-1 K-1 used by Anderson (1976). Lower values will slow snowmelt. To turn off SMLT, set MELFAC to zero. [see SNO-SNOENRGY]
MESFL and MESFLN (Input variable) - measured
streamflow for the date, mm. In code MESFLN is MESFL for the next day. MESFL
is used only for output and statistical comparison with simultaed
FLOW. If there is no measured streamflow, MESFL must
be zero. If a precipitation interval input file is used then MESFL is ignored
unless MESFLP is -1.
MESFLD, MESFLM, MESFLY - measured streamflow, mm.
MESFLP (Input variable) - average measured streamflow rate for precip interval, mm/d. MESFLP is used only for output and statistical comparison with simulated FLOW. Note MESFLP is the streamflow rate, not the total for the interval. If MESFLP is not available it must be set to -1; then MESFL is used instead for the whole day.
ML - the maximum number of soil layers allowed by BROOK90, currently set at 25. ML can be increased up to 50, but this requires recompilation. The limit of 50 is set by the dimension of local variables in subroutines PLNTRES, SOILPAR, TBYLAYER, INFPAR, and ITER.
MXKPL (Canopy parameter) - maximum plant conductivity, mm d-1 MPa-1. The internal resistance to water flow through the plants RPLANT = 1 / (MXKPL * RELHT * DENSEF). MXKPL is the main controller of soil-water availability and is a property of all of the plants on a unit area, not of any one plant. When the canopy is at its maximum seasonal LAI and height, and when soil is wet so that soil water potential is effectively zero, and when the leaf water potential is at its critical value, PSICR, then MXKPL is the transpiration rate divided by PSICR. Abdul-Jabbar et al. (1988) found that MXKPL ranges only from 7 to 30 mm d-1 MPa-1 over a wide range of vegetations, a surprisingly constant parameter. A transpiration rate of 0.5 mm/hr at a gradient of -1.5 MPa is typical, giving MXKPL of 8 mm d-1 MPa-1 (Hunt et al. 1991). MXKPL controls the rate of water supply to the leaves and thus the transpiration when soil water supply is limiting. Decreasing MXKPL makes soil water less available and thus reduces actual transpiration below potential transpiration at higher soil water content. [see PET-CANOPY] [see EVP-PLNTRES]
MXRTLN (Canopy parameter) - maximum length of fine roots per unit ground area, m/m2. Total root length per unit area (RTLEN) is MXRTLN * RELHT * DENSEF. MXRTLN is used to calculate rhizosphere resistance and is only important when soil is dry or roots are sparse. Values of MXRTLN are not frequent in the literature, especially for forests. Newman (1974) reported a range of 1700 to 11000 m/m2 for 5 woody plants. Safford (1974) found fine root masses of 1200 g/m2 for northern hardwoods, and Safford and Bell (1972) found 700 g/m2 for white spruce; with a mean diameter of 0.7 mm and density of 0.5 g/cm3, these become 6200 and 3600 m/m2. To turn off TRAN set MXRTLN to zero. [see PET-CANOPY] [see EVP-PLNTRES]
N - index variable for precipitation interval.
NN (Fixed parameter) - wind/diffusivity extinction coefficient, dimensionless. NN is the canopy extinction coefficient for wind and eddy diffusivity. NN is fixed at 2.5 following Shuttleworth and Gurney (1990). Federer et al. (1995) show that PE is insensitive to the value of n, but they did not test sparse canopies in a wet climate. [see PET-SWGRA]
NDAYS - number of days in run. NDAYS is the sum of the number of initializing days and the number of output days from the main window, and is the number of times the day loop is to be entered.
NITS - number of iterations in precipitation
interval.
NITSD - total number of iterations for day.
NITSM - total number of iterations for month.
NITSY - total number of iterations for year.
NITSR - total number of iterations for run.
NLAYER (Soil parameter) - number of soil layers to be used, dimensionless. NLAYER is the number of soil layers to be used in the model run. It can vary from 1 to ML. Run time is more or less proportional to NLAYER. Soil parameter values for layers greater than NLAYER can be 0.
NOOUTF (Fixed parameter) - 0 to allow outflow from roots, 1 for no outflow. NOOUTF is a switch that when set to 1 prevents outflow from the plant roots to the soil when soil is dry. NOOUTF = 0 allows such outflow, so water can move from wet soil layers to dry soil layers through the roots. [see EVP-TBYLAYER]
NPINT - number of precipitation intervals per day. NPINT is obtained by reading the beginning of the precipitation interval file. If no such file is selected, NPINT = 1. The precipitation interval file has one line for each precipitation interval for each day, e.g. 4 lines for 6-hour precipitation. The maximum allowed NPINT is 240 (6-minute intervals).
NTFLI(1 To ML) - net flow rate into layer, mm/d.
[see WAT-INFLOW]
[see WAT-ITER]
NTFLPI(1 To ML), NTFLDI(1 To ML), NTFLMI(1 To ML), NTFLYI(1 To ML) - net
flow into layer, mm.
PINT - average potential interception rate for the
day, mm/d. This is the interception evaporation that would occur for a canopy continually
wet.
[see EVP-INTER]
[see EVP-INTER24]
PINTD, PINTM, PINTY - potential interception for a canopy always wet, mm.
PIR(2) - potential interception rate for daytime and nighttime, mm/d.
[see PET]
PREC - precipitation rate, mm/d.
PRECD, PRECM, PRECY - precipitation, mm.
PREINT (Input variable) - precipitation for precipitation interval, mm. PREINT is read from the precipitation interval file when one is selected. Otherwise, NPINT = 1 and PRECINT = PRECIN.
PRECIN (Input variable) - daily precipitation, mm. PRECIN is read from the daily input file. If a precipitation interval file has been selected, PRECIN is ignored and PREINT is used.
PSICR (Canopy parameter) - minimum plant leaf water potential, MPa. PSICR is the critical leaf water potential at which stomates close. BROOK90 assumes that transpiration is limited by potential transpiration (PTRAN) until water uptake at a plant water potential of PSICR is less than PTRAN. PSICR can be considered as the water potential at the turgor-loss point. PSICR varies from -1.5 to -3.0 MPa for most species and is quite species dependent (Hinckley et al. 1978). This parameter is best selected from knowledge of the water potential - diffusion resistance relation for the species involved. [see KPT-SOILPAR] [see EVP-TBYLAYER]
PSIF(1 To ML) (Soil parameter) - matric potential at "field capacity" corresponding to KF and THETAF for a soil layer, kPa. PSIF replaces the more usual but conceptually questionable value of air entry value in the Clapp and Hornberger (1978) equations. The concept of field capacity is not used for matric flow of soil water, but is used to calculate SLVP, SRFL, BYFL, and ADEF. [see KPT for much more on PSIF] [see PET-FRSS]
PSIG(1 To ML) - gravity potential for soil layer, kPa. Calculated parameter PSIG is the gravity potential of the middle of the soil layer, with the soil surface as zero. It is calculated from THICKwhen the Soil Parameter window loads. When THICK is changed, Check will show the new PSIG values, though this is not necessary. PSIG only shows a non-zero value for NLAYER soil layers. [see KPT-SOILPAR]
PSIM(1 To ML) and PSIMIN(1 To ML) (Initial value) - matric soil water potential for layer and its initial value, kPa. In code PSIMN is the initial value. BROOK90 uses water potential rather than water content as the initial variable because water potential is much less variable among layers at any given time . Initiating water potentials for all layers at the same value is appropriate even when the soil texture differs widely among layers. Furthermore, initial potential need not be changed when layer thickness or properties are changed. Initiating water potentials for all layers at the same value is appropriate even when the soil texture differs widely among layers. If soil is relatively wet, the effect of initial PSIM values only lasts a few days. Initializing PSIM = PSIF can be appropriate when PSIF is defined at "field capacity". [see KPT] [see PET-FRSS] [see WAT-DSLOP]
PSITI(1 To ML) - total soil water potential for a layer, kPa [see KPT-SOILPAR] [see EVP-TBYLAYER] [see WAT-VERT]
PSNVP - potential snow evaporation, mm/d. [see SNO-SNOVAP] [see SNO-SNOWPACK]
PTR(1 To 2) - potential
transpiration rate for daytime or night, mm/d
[see PET]
PTRAN - average potential transpiration rate for day, mm/d.
PTRAND, PTRANM, PTRANY - potential transpiration, mm.
QDEPTH (Flow parameter) - soil depth for SRFL calculation, mm. QDEPTH determines the number of soil layers over which wetness is calculated to determine source area fraction and SRFL. QDEPTH does not need to correspond to the bottom of a soil layer, but it is converted into the number of soil layers most closely corresponding to QDEPTH. When QDEPTH equals or exceeds the depth of NLAYER then all NLAYERs are used. When QDEPTH = 0, the source area fraction is equal to IMPERV. Smaller QDEPTH means a larger contrast between wet and dry conditions, and thus more responsiveness of source area fraction. See also QFPAR and QFFC. To turn off SRFL set both IMPERV and QDEPTH to zero. [see WAT-BYFLFR] [see WAT-SRFLFR] [see WAT-SRFPAR]
QFFC (Flow parameter) - quick flow fraction for SRFL and BYFL at THETAF, dimensionless. QFFC is used for both SRFL and BYFL, so normally only one or the other should be simulated. For Hubbard Brook Watershed 6, QFFC = 0.2 and QFPAR = 0.3 fit storm hydrographs well using SRFL; these values give a generally high stormflow response. Decreasing QFFC decreases SRFL and BYFL proportionally at all soil water contents. See also QFPAR, and QDEPTH. QFFC must be greater than 0.0001. When both BYPAR and QDEPTH = 0, QFFC is ignored. When QFFC = 1 there is never any infiltration into the top soil layer. [see WAT-BYFLFR] [see WAT-SRFLFR]
QFPAR (Flow parameter) - fraction of the water content between field capacity (THETAF) and saturation (THSAT) at which the quick flow fraction is 1, dimensionless. QFPAR is used for both SRFL and BYFL, so normally only one or the other should be simulated. When QFPAR = 0 (<= 0.01), quick flow operates like a field-capacity bucket; all water input above field capacity becomes BYFL or SRFL. For Hubbard Brook Watershed 6, QFFC = 0.2 and QFPAR = 0.3 fit storm hydrographs well using SRFL; these values give a generally high stormflow response. Increasing QFPAR increases quickflow from soil dryer than THETAF and decreases it from soil wetter than THETAF. Values > 1 are allowed. For SRFL, the average water content of layers down through QDEPTH controls the flow rate. For BYFL, the water content of each layer controls the flow rate from that layer. When both BYPAR and QDEPTH = 0, QFPAR is ignored. [see WAT-BYFLFR] [see WAT-SRFLFR]
R5 (Fixed parameter) - solar radiation at which stomatal conductance is half of its value at RM, W/m2. Values in the range of 50 to 200 W/m2 are likely for many species. BROOK90 fixes R5 = 100 W/m2 as the default for all cover types because insufficient data are available to describe R.5 by cover type (Körner 1994). [see PET-SRSC]
RAA - Shuttleworth-Wallace
atmosphere aerodynamic resistance,s/m.
[see PET-SWGRA]
[see SNO-SNOVAP]
RAC - Shuttleworth-Wallace canopy aerodynamic resistance, s/m.
[see PET-SWGRA]
RAS - Shuttleworth-Wallace ground aerodynamic resistance, s/m.
[see PET-SWGRA]
[see SNO-SNOVAP]
RATIO - the fraction of leaf area that is not buried by snow, assuming a uniform vertical distribution of leaf area [see PET-CANOPY]
RELHT(1 To 20) (Location parameter) - array of ten pairs of day of the year (DOY) and relative height between 0 and 1, dimensionless. RELHT allows canopy height to vary through the year and is a multiplier of MAXHT. The DOY values must increase; intermediate values are interpolated linearly. The first DOY used must be 1 and a later DOY value must be 366. Any remaining pairs after DOY 366 are ignored. RELHT different from 1 would generally be used for herbaceous plant covers. The phenology of RELHT must be determined externally to BROOK90, and is location as well as cover type dependent. [see PET-CANOPY]
RELLAI(1 To 20) (Location parameter) - array of ten pairs of DOY and relative LAI between 0 and 1, dimensionless. RELLAI allows LAI to vary through the year and is a multiplier of MAXLAI. The doy values must increase; intermediate values are interpolated linearly. The first DOY must be 1 and a later DOY value must be 366. Any remaining pairs after DOY 366 are ignored. The phenology of RELLAI must be determined externally to BROOK90, and is location as well as cover type dependent. [see PET-CANOPY]
RFAL - rainfall rate, mm/d.
RFALD, RFALM, RFALY - rainfall, mm.
RHOWG - constant density of water times gravity acceleration, 0.00981 MPa/m or kPa/mm. [see KPT-SOILPAR] [see EVP-PLNTRES] [see EVP-TBYLAYER] [see WAT-VERT] [see WAT-DSLOP]
RHOTP (Fixed parameter) - ratio of total leaf area to projected area, dimensionless. RHOTP is always 2 for broadleaves, and ranges from 2 for flat needles to π for cylindrical needles. RHOTP is fixed at 2. The difference between 2 and 3 is generally negligible. [see PET-SWGRA] [see PET-SRSC]
RINT - rainfall catch rate, mm/d. To turn off
RINT, set both FRINTL and FRINTS to zero.
[see EVP-INTER]
RINTD, RINTM, RINTY - rain interception, mm.
RM (Fixed parameter) - nominal maximum solar radiation possible on a leaf, W/m2, as used in calculating leaf conductance. See also R5. RM is fixed at 1000 W/m2. [see PET-SRSC]
RNET - rain reaching soil surface, mm/d.
[see SNO-SNOWPACK]
[see WAT-SRFLFR]
RNETD, RNETM, RNETY - rainfall to soil surface, mm.
ROOTDEN (1 To ML) (Canopy parameter) - relative root density (per unit stonefree volume) of fine or absorbing roots for given layer, m3/m3. In code ROOTDEN is the array of pairs of layer thickness (mm) and relative density. The layers do not need to correspond to the soil layers in Soil Parameters. The program allocates roots from the ROOTDEN layers to the soil layers. Thickness and density values may all be zero. It is convenient to specify the relative density in the top layer as 1, but this is not necessary; the actual sum of the density values is not relevant. Together with FXYLEM, this parameter controls the relative transpiration from each layer. The total root length by layer is obtained from ROOTDEN, MXTRTLN, and STONEF (as well as RELHT nd DENSEF if they are < 1). Gerwitz and Page (1974) found that root distribution with depth was exponential for many crops. Jackson et al. (1996) provide exponential fit parameters for major cover types. In forest soils, the relative density is very high in the O horizon; fine root density in the top 5 cm can be ten times the density at 20 cm (Safford and Bell 1972, Safford 1974). [see WAT-RTDEN] [see EVP-PLNTRES]
RPLANT - plant resistivity to water flow, MPa d/mm. [see EVP-CANOPY] [see EVP-PLNTRES]
RROOTI(1 To ML) - root resistance for layer, MPa d/mm. [see EVP-PLNTRES] [see EVP-TBYLAYER]
RSC - Shuttleworth-Wallace canopy surface resistance, s/m. [see PET-SRSC]
RSNO - rain added to snowpack, mm/d.
[see SNO-SNOWPACK]
RSNOD, RSNOM, RSNOY - rain on snow, mm.
RSS - Shuttleworth-Wallace soil surface resistance, s/m. [see PET-FRSS]
RSSA (Fixed parameter) - soil evaporation resistance (RSS) at field capacity, s/m. RSSA is the soil surface resistance to soil evaporation at field capacity as defined by PSIF. There is essentially no information on how this parameter varies with the characteristics of the surface soil layer, particularly for forests. RSSA is fixed at 500 s/m following Shuttleworth and Gurney (1990). To eliminate SLVP set RSSA to zero. [see PET-FRSS]
RSSB (Fixed parameter) - exponent in relation of soil evaporation resistance (RSS) to soil water potential (PSIM) in the top layer, dimensionless. There is essentially no information on how this parameter varies. RSSB is fixed at 1.0, which makes RSS directly proportional to PSIM. Setting RSSB = 0 makes the soil evaporation resistance always equal to RSSA. [see PET-FRSS]
RSTEMP (Location parameter) - base temperature for snow-rain transition, °C. The fraction of daily precipitation as snow is (RSTEMP - TMIN) / (TMAX - TMIN) when TMIN < RSTEMP < TMAX. Lowering RSTEMP produces more snow. RSTEMP = -100 turns off SFAL and makes all precipitation rain. [see SNO-SNOFRAC]
RTHR - rain throughfall rate, mm/d.
[see SNO-SNOWPACK]
RTHRD, RTHRM, RTHRY - rain throughfall, mm.
RTLEN - root length per unit land area, m/m2 [see PET-CANOPY]
RTRAD (Fixed parameter) - average root radius, mm. RTRAD is the average radius of the fine or water-absorbing roots. It is only relevant to transpiration from dry soil. RTRAD is fixed at 0.35 mm. [see EVP-PLNTRES]
RXYLEM - xylem resistance, MPa d/mm. [see EVP-PLNTRES]
SAFRAC - source area fraction. [see WAT-SRFLFR]
SAI - projected stem area index, m2/m2. SAI is the projected surface area of stems, branches, and twigs above a unit ground area when the projected area is defined by the widest cross section through the objects. If all objects were cylindrical, the ratio of total to projected surface area would be π. SAI is defined here by projection to be equivalent to the normal use of projected LAI. SAI = CS * HEIGHT * DENSEF. [see SUN-AVAILEN] [see PET-SWGRA] [see PET-CANOPY] [see EVP-INTER] [see SNO-SNOENRGY]
SAIMLT (Fixed parameter) - snowmelt dependence on SAI, dimensionless. Melt is linearly proportional to exp (-SAIMLT * SAI); so melt decreases exponentially as SAI increases. SAIMLT is fixed at 0.5. With SAIMLT = 0.5 and LAIMLT = 0.2 , melt in deciduous forest (LAI=0, SAI=0.7) is 0.70 times that in the open, and melt in conifer forest (LAI=6, SAI=0.7) is 0.21 times that in the open. Federer et al. (1973b) generalized literature ratios to 0.5 for deciduous/open and 0.25 for conifer/open. Matching their results with the exponential algorithm would require greater difference between LAIMLT and SAIMLT, but it is difficult to see why they should differ much. [see SNO-SNOENRGY]
SC - solar constant, value from Lean (1991), 1367.0 W/m2. [see SUN-SUNDS]
SEEP - deep seepage loss from groundwater, mm/d.
To eliminate SEEP set GSP to zero.
[see WAT-GWATER]
SEEPP, SEEPD, SEEPM, SEEPY - seepage loss, mm.
SFAL - snowfall rate, mm/d. To turn off SFAL set
RSTEMP to -100; then all precipitation is rain regardless
of temperature.
SFALD, SFALM, SFALY - snowfall, mm.
SHEAT - average subsurface heat flux for the day, W/m2. The subsurface heat flux, S, includes all temperature changes, and thus heat storage changes, in the vegetation, the canopy air, the soil, and any snow. This term is frequently ignored for daily time intervals, but it becomes more important for both shorter (diurnal variation) and longer (seasonal variation) times, particularly for bare soils. SHEAT is set to zero in Module B90V4.BAS. Any change to this assumption would required recoding. [see SUN-AVAILEN]
SIGMA - Stefan-Boltzmann constant, 5.67x10-8 W m-2 K-4. [see SUN-AVAILEN]
SINT - snowfall catch rate, mm/d. To turn off
SINT, set both FSINTL and FSINTS to zero.
[see EVP-INTER]
SINTD, SINTM, SINTY - snow interception, mm.
SLFDAY - ratio of potential insolation on slope to horizontal, map area [see SUN-SUNDS] [see SNO-SNOENRGY]
SLFL - input rate to soil surface, mm/d. To turn
off SLFL set IMPERV = 1.
[see WAT-SRFLFR]
[see WAT-INFLOW]
SLFLP, SLFLD, SLFLM, SLFLY - input to soil surface, mm.
SLFLI(1 To ML) - macropore infiltration rate down from layer, mm/d.
SLFLPI(1 To ML), SLFLDI(1 To ML), SLFLMI(1 To ML), SLFLYI(1 To ML) -
vertical macropore infiltration from layer, mm.
SLRAD - average solar radiation on slope over daytime, W/m2. [see SUN-AVAILEN]
SLVP - evaporation rate from soil, mm/d. To turn
off SLVP set RSSB to zero.
[see PET]
SLVPD, SLVPM, SLVPY - soil evaporation, mm.
SMLT - melt drainage rate from snowpack, mm/d.
To turn off SMLT, set MELFAC to zero.
[see SNO-SNOWPACK]
[see WAT-SRFLFR]
SMLTD, SMLTM, SMLTY - snowmelt, mm.
SNODEN (Fixed parameter) - snow density, mm/mm. SNODEN is the snowpack density or the ratio of water content to depth. SNODEN is used only to correct leaf area index and stem area index to the fraction of them that is above the snow. It does not vary with time or snowpack ripeness in BROOK90. SNODEN is fixed at 0.3. [see PET-CANOPY]
SNODEP - snow depth, m. SNODEP is SNODEN * SNOW and is used only to reduce HEIGHT of the canopy. [see PET-CANOPY]
SNOEN - energy flux density to snow surface, MJ m-2 mm-1 d-1. [see SNO-SNOENRGY] [see SNO-SNOWPACK]
SNOFRC - fraction of precipitation for the day as snow, unitless. [see SNOW and SNOWIN (Initial value) - water equivalent of snow on the ground, mm. In code SNOWIN is the initial value. This initial SNOW is assumed to have no liquid water content and to have a temperature of 0°C, i.e. no cold content (CC).Initial value effects for SNOW can last for days to months. [see SNO-SNOWPACK]
SNOWLQ - liquid water content of snow on the ground, mm. [see SNO-SNOWPACK]
SNVP - evaporation rate from snowpack, mm/d. To
turn off SNVP set KSNVP to zero.
SNVPD, SNVPM, SNVPY - evaporation from snowpack, mm.
[see SNO-SNOVAP]
SOLRAD (Input variable) - solar radiation for the day on a horizontal surface, MJ/m2. If input SOLRAD is zero, it is estimated as a constant fraction of potential solar radiation (I0HDAY). The default fraction is 0.55, but as of Version 4.8 it can be changed. If SOLRAD exceeds 0.99 * I0HDAY, it is reduced to that value. [see PET-WEATHER] [see SUN]
SRFL - source area flow rate, mm/d. To turn off
SRFL set both IMPERV and QDEPTH
to zero.
[see WAT-SRFLFR]
SRFLP, SRFLD, SRFLM, SRFLY - source area flow, mm.
STHR - snow throughfall rate, mm/d.
[see SNO-SNOWPACK]
STHRD, STHRM, STHRY - snow throughfall, mm.
STONEF(1 To ML) (Soil parameter) - stone volume fraction in each soil layer, dimensionless. STONEF is the fraction of the total layer that is coarse fragments, which are assumed to neither store nor conduct water. STONEF reduces water storage capacity and both downslope and vertical matric flow. STONEF is usually estimated in soil surveys. It can, of course, be set to zero, but for many forest soils, values of 0.1 to 0.4 are more appropriate. [see EVP-PLNTRES] [see KPT] [see WAT-VERT] [see WAT-DSLOP]
STORD, STORM, STORY - total water storage in system, mm.
STRES - TRAN / PTRAN for time period.
SWAT - total soil
water in all layers, mm.
SWATI(1 To ML) - soil water volume in layer, mm.
SWATMX(1 To ML) - maximum water storage for layer, mm. [see KPT-SOILPAR] [see WAT-ITER]
SWATQF - water storage at field capacity for layers 1 to ,mm, calculated parameter. [see WAT-SRFLFR] [see WAT-SRFPAR]
SWATQX - maximum water storage for layers 1 to QLAYER, mm, calculated parameter. [see WAT-SRFLFR] [see WAT-SRFPAR]
TA - mean temperature for the day at reference height,
°C. Calculated as 0.5 * (TMAX +
TMIN).
[see PET-WEATHER]
[see PET-SRSC]
[see SNO-SNOENRGY]
[see SNO-SNOWPACK]
TADTM - average daytime temperature at
reference height, °C.
[see PET-WEATHER]
TANTM - average nighttime temperature at reference height, °C.
[see PET-WEATHER]
TAJ - TADTM or TANTM depending on index J.
TH, T1, T2, and TL - input parameters- temperatures controlling when stomates are closed, °C. TL, T1, T2, and TH express the reduction of leaf conductance caused by sub-optimal temperature. When the mean air temperature for the day (TA) is less than TL or greater than TH, stomates are closed and GLMIN applies. When TA is between T1 and T2, there is no stomatal closure induced by suboptimal temperature. BROOK90 uses a parabolic interpolation when TA is in the TL to T1 and T2 to TH ranges. If TL = T1 and TH = T2 the temperature response is square. When TL and T1 are very low and T2 and TH are very high there is no temperature effect on leaf conductance. There is very little data on temperature response by species as it is difficult to separate from the vapor pressure response (Körner 1994). Values are TL = 0°C, T1 = 10°C, T2 = 30°C, and TH = 40°C are reasonable choices. [see PET-SRSC]
THETA(1 To ML) - water content, mm water / mm soil matrix [see KPT]
THETAF(1 To ML) (Soil parameter) - volumetric water content at "field capacity" corresponding to KF and PSIF for soil layer, m3/m3. THETAF replaces the more usual value of saturated water content in the Clapp and Hornberger (1978) equations. The concept of field capacity is not used for matric flow of soil water, but is used to calculate SLVP, SRFL, BYFL, and ADEF. THETAF is normally obtained for the given PSIF from θ - ψ curves that are obtained from laboratory analysis of soil cores. [see KPT]
THICK(1 To ML) (Soil parameter) - layer thicknesses, mm. THICK is the vertical thickness of each soil layer. Each layer can have a different thickness, but the number of iterations goes up as the thickness of any layer goes down. THICK should probably not be less than 50 mm unless run time is not important. [see EVP-PLNTRES] [see KPT] [see WAT-VERT]
THSAT(1 To ML) (Soil parameter) - THETA at saturation, m3/m3. THSAT is the matrix porosity (volume fraction) by layer and is also the water content by volume at saturation. THSAT is only important when the soil is nearly saturated due to impeded vertical flow. [see KPT]
TMAX and TMIN (Input variables) - maximum and minimum temperatures for the day, °C. BROOK90 has no provision for adjusting temperatures for elevation. If the location being simulated differs in elevation from the weather station elevation, the input temperatures could be adjusted externally to BROOK90 by the environmental lapse rate of -0.06°C/100 m (Ollinger et al. 1995). [see PET-WEATHER] [see SNO-SNOFRAC]
TRANI(1 To ML) - average transpiration rate from
layer, mm/d. To turn off all TRANI set MXRTLN to zero.
[see WAT-INFLOW]
TRANP, TRAND, TRANM, TRANY - transpiration, mm.
TRANPI(1 To ML), TRANDI(1 To ML), TRANMI(1 To ML), TRANYI(1 To ML) - -
layer transpiration, mm.
TSNOW - snowpack temperature (assumed isothermal), °C. [see SNO-SNOVAP]
UA - average wind speed for the day at reference
height, ZMINH plus HEIGHT, m/s.
[see PET-WEATHER]
[see PET-WNDADJ]
UADTM, UANTM, and UAJ - average wind
speed for daytime, nighttime, or either (depending on J) at
reference height, m/s.
[see PET-WEATHER]
UW (Input variable) - average wind speed for day, m/s. If input UW is zero, UW defaults to 3 m/s; as of Version 4.8 this can be changed. Measured zero wind speed should be input as 0.1; input values >0 and <0.2 are set to 0.2 m/s. If wind speed was measured above the surface being simulated rather than at a weather station, set Z0W = 0. Otherwise, UA is calculated from UW based on ZW, Z0W, and FETCH. [see PET-WEATHER] [see PET-WNDADJ]
VPD - vapor pressure deficit at reference height, kPa. [see PET-PM] [see PET-SRSC]
VRFLI(1 To ML) -
vertical matrix drainage rate from layer, mm/d. To prevent drainage from the
bottom layer set DRAIN to zero.
[see WAT-VERT]
[see WAT-INFLOW]
[see WAT-GWATER]
VRFLPI(1 To ML), VRFLDI(1 To ML), VRFLMI(1 To ML), VRFLYI(1 To ML) -
vertical matrix drainage from layer, mm.
VV(1 To ML) - temporary VRFLI.
[see WAT-INFLOW]
WETC(1 To ML) - wetness at PSICR, dimensionless, calculated parameter. [see KPT-SOILPAR]
WETF(1 To ML) - wetness at field capacity, dimensionless, calculated parameter [see KPT] [see WAT-BYFLFR]
WETFR - fraction of precipitation interval that canopy is wet.
WETINF(1 To ML) (Soil parameter) - wetness at dry end of near-saturation range for a soil layer, dimensionless. WETINF is the wetness (saturation fraction) at the inflection point in the Clapp-Hornberger (1978) equation. This value is the lower limit of the parabolic approach to saturation. BROOK90 changes WETINF if it is outside the range from BEXP/(1+BEXP) to 0.999. [see KPT]
WETNES(1 To ML) - wetness, fraction of saturation. [see KPT] [see WAT-BYFLFR] [see WAT-ITER]
WNDRAT (Fixed parameter) - average ratio of nighttime to daytime wind speed, dimensionless. WNDRAT is fixed at 0.3. The value is based on Hubbard Brook data and could be changed if a better value were known. [see PET-WEATHER]
WTOMJ - constant unit conversion, 0.0864(MJ m-2 d-1)/(watt/m2) = 86400 s/d * 0.000001 MJ/J. See also ETOM. [see SUN-AVAILEN]
YY (Input variable) - two-digit year.
Z0 - canopy roughness parameter, m. [see PET-ROUGH]
Z0C - roughness parameter for closed canopy of HEIGHT, m. [see PET-ROUGH]
Z0G (Fixed parameter) - ground surface roughness, m. Z0G is the roughness parameter of the ground surface below the canopy. It controls the amount of turbulent transfer at the ground surface, and thus soil evaporation. It should generally be on the order of a few centimeters, but the value probably doesn't matter much. See also Z0S. In code, Z0GS is Z0S when snow is present and Z0G with no snow. [see PET-ROUGH] [see PET-SWGRA]
Z0GS - ground or snow surface roughness parameter, m. [see PET-ROUGH]
Z0S (Fixed parameter) - roughness parameter of snow surface, m. Z0S used in place of Z0G when there is snow on the ground. Z0S is fixed at 0.001 m. In code, Z0GS is Z0S when snow is present and Z0G with no snow. [see PET-ROUGH]
Z0W (Fixed parameter) - roughness parameter at the weather station where wind speed was measured, m. Used to adjust UW to wind speed at reference height above the surface being simulated. If wind speed was actually measured above the surface being simulated set Z0W = 0, then UA = UW and FETCH and ZW are ignored. Z0W of 0.005 m is appropriate for a short grass surface. [see PET-WNDADJ]
ZA - reference height for TA, EA, UA, above ground, m. [see PET-ROUGH] [see PET-WNDADJ] [see SNO-SNOVAP]
ZMINH (Fixed parameter) - reference height for weather data above canopy HEIGHT, m. ZA is ZMINH + RELHT * MAXHT, which can vary seasonally. ZMINH is fixed at 2 m. [see PET-ROUGH]
ZW (Fixed parameter) - weather station measurement height for wind, m. ZW is the height above the ground at which wind speed (UW) was measured. ZW is fixed at 10 m. Unless more is known about the wind speed weather station, ZW, FETCH, and Z0W should not be changed. ZW is ignored if Z0W = 0. [see PET-WNDADJ]