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: Text S1
Model Calibration
Calibration of TEM-Hydro involves adjusting several parameters to get the site specific (targeted) carbon in vegetation and soils such as total vegetation and soil carbon, GPP, Nitrogen-limited Net Primary Production (NPP), nitrogen-saturated NPP, and available inorganic nitrogen. The model is calibrated to develop parameter values for photosynthesis (cmax), uptake of inorganic nitrogen (nmax), maintenance respiration (kr), heterotrophic respiration (kd), and vegetation carbon ( th e a r t w o o d ) . O u r c a l i b r a t i o n s i t e s a r e H a r v a r d F o r e s t , M A f o r t e m p e r a t e d e c i d u o u s f o r e s t ( o a k , m a p l e ) a n d t e m p e r a t e c o n i f e r o u s f o r e s t ( p i n e ) , B o n a n z a C r e e k , A K f o r b o r e a l f o r e s t ( s p r u c e ) , P a w n e e g r a s s l a n d s , C O , a p r e d o m i n a n t l y C 4 s h o r t g r a s s l a n d , a n d C u r lew shrubland, UT, a mixed C3 deciduous and C4 evergreen shrubland. For C3 vegetation we assume a half saturation constant (kc) of 200 for the effects of CO2 fertilization, consistent with ADDIN EN.CITE Felzer2009127[, 2009]12712717Felzer, B. S.Cronin, T. W.Melillo, J. M.Kicklighter, D. W.Schlosser, C. A.Importance of carbon-nitrogen interactions and ozone on ecosystem hydrology during the 21st centuryJGR-BiogeosciencesJGR-Biogeosciences114Journal Article2009[HYPERLINK \l "_ENREF_7" \o "Felzer, 2009 #127"Felzer et al., 2009]. For C4 vegetation we assume a low kc value of 40. We assume Pawnee is a 30/70 C3/C4 mix and Curlew is 50/50. Final calibrated values are given in the Table S1. Other biome-dependent parameters are given in Table S2 and biome independent parameters in Table S3. Target carbon and nitrogen stock and flux values for each biome are given in Table S4. USGS stream gauges used for validation are given in Table S5.
Running Means: Many new variables are running means; the timescale used to calculate them is based on the characteristic timescale for turnover of living plant tissue. Some of the specific usages of running means are included in the descriptions below.
Canopy Conductance: The canopy conductance (gc) is according to Ball et al. ADDIN EN.CITE Ball198724[1987]242417Ball, J. T.Woodrow, I. E.Berry, J. A.A model predicting stomatal conductance and its contribution to the control of photosynthesis under different environmental conditionsProgress in Photosynthesis ResearchProgress in Photosynthesis ResearchISBN9024734533IVJournal Article1987[HYPERLINK \l "_ENREF_2" \o "Ball, 1987 #24"1987]:
where gsmin is minimum stomatal aperture (mmol m-2 s-1), gsa is the stomatal slope (unitless), LAI is the leaf area index, GPP is the Gross Primary Productivity, RH is the relative humidity, Ca is the ambient carbon dioxide concentration, and gs is the average stomatal conductance.
Aerodynamics and Windspeed: To better account for the effects of broad climatological variations in windspeed on surface energy fluxes, we now read in a windspeed dataset. This is used, together with vegetation height, to determine aerodynamic resistances within the soil-canopy-atmosphere system. These aerodynamic resistances are used in the Shuttleworth and Wallace ADDIN EN.CITE Shuttleworth1985860[1985]86086017Shuttleworth, W. J.Wallace, J. S.Evaporation from sparse crops: an energy combination theoryQuarterly Journal of the Royal Meteorological Society839-8551111985[HYPERLINK \l "_ENREF_10" \o "Shuttleworth, 1985 #860"1985] evapotranspiration formula. The formulations below are from Choudhury and Monteith ADDIN EN.CITE Choudhury198863[1988]636317Choudhury, B. J.Monteith, J. L.A four-layer model for the heat budget of homogeneous land surfacesQuarterly Journal of the Royal Meteorological SocietyQuarterly Journal of the Royal Meteorological Society373-398114Journal Article1988[HYPERLINK \l "_ENREF_4" \o "Choudhury, 1988 #63"1988], Federer et al. ADDIN EN.CITE Federer1996123[1996]12312317Federer, C. A.Vorosmarty, C. J.Fekete, B.Intercomparison of methods for calculating potential evapotranspiration in regional global water balance modelsWater Resources ResearchWater Resources Research2315-232132Journal Article1996[HYPERLINK \l "_ENREF_6" \o "Federer, 1996 #123"1996] and Zhou et al. ADDIN EN.CITE Zhou2006538[2006]53853817Zhou, M. C.Ishidaira, H.Hapuarachchi, H. P.Magome, J.Kiern, A. S.Takeuchi, K.Estimating potential evapotranspiration using Shuttleworth-Wallace model and NOAA-AVHRR NDVI data to feed a distributed hydrological model over the Mekong River basinJournal of HydrologyJournal of Hydrology151-1733271-22006[HYPERLINK \l "_ENREF_11" \o "Zhou, 2006 #538"2006].
EMBED Equation.3 (1)
EMBED Equation.3 (2)
EMBED Equation.3 (3)
where rac = leaf-to-canopy aerodynamic resistance, ras = soil-to-canopy aerodynamic resistance, raa = canopy-to-screen height aerodynamic resistance, wleaf = biome-dependant parameter, and
EMBED Equation.3
EMBED Equation.3
EMBED Equation.3
EMBED Equation.3
EMBED Equation.3
EMBED Equation.3
EMBED Equation.3
where ua = windspeed at 2 m above the canopy, zh = canopy height, za = reference height 2 m above canopy, zd = displacement height, u* = friction velocity, and neddy = eddy resistance coefficient. The friction velocity depends on the windspeed and roughness length (zo). The roughness length depends on the canopy density and canopy height. The displacement height depends on the canopy height and LAI. Other variables are: u = windspeed at 10 m height, href = biome-dependent reference height, kallom = biome-dependent parameter, cabove = total above ground biomass in kg C m-2, k_karman constant = 0.41. The canopy aerodynamic resistance (rac) decreases as LAI and u* increase; the more air is moving through a denser canopy, the more coupled the canopy is to the air. Neddy is related to a turbulent closure parameterization; as it increases with vegetation height, the soil is more and more cut off from the atmosphere (e.g. ras becomes larger).
Internal Leaf CO2: The internal leaf CO2 (ci) is now consistent with the calculation of GPP and stomatal conductance, assuming that the CO2 on the leaf surface is equal to the atmospheric CO2. The equations to be solved for ci simultaneously are:
EMBED Equation.3 (4)
EMBED Equation.3 (5)
EMBED Equation.3 (6)
where cmax = maximum leaf-level photosynthetic rate, fpar = canopy integrated light response function, temp = GPP dependence on temperature, kc = half-saturation constant of CO2 fertilization, 1.563 = ratio of molecular diffusivity of water vapor to carbon dioxide ((44/18)0.5), ca = atmospheric CO2 level, gsmin = minimum stomatal aperture (mmol m-2 s-1), gsa = stomatal slope, rl = leaf growth and maintenance respiration (mmol m-2 s-1), and RH = relative humidity. The simultaneous solution of ci involves the solution to a quadratic equation. The solution is:
EMBED Equation.3
EMBED Equation.3
EMBED Equation.3
This solution can be thought of graphically by plotting the equation for GPP from (4) together with the equation for GPP from (5) and (6) (after eliminating gc), as the dependent variable, with the independent variable being ci. Ci tends to lie in between ca and 0; though for ra > GPP, it may be larger. When the gsmin*LAI term and rl are negligible in equation (6), this expression tends toward the open-stomata limit used in Felzer et al. ADDIN EN.CITE Felzer2009127[2009]12712717Felzer, B. S.Cronin, T. W.Melillo, J. M.Kicklighter, D. W.Schlosser, C. A.Importance of carbon-nitrogen interactions and ozone on ecosystem hydrology during the 21st centuryJGR-BiogeosciencesJGR-Biogeosciences114Journal Article2009[HYPERLINK \l "_ENREF_7" \o "Felzer, 2009 #127"2009].
Canopy Interception: Canopy interception is now explicitly calculated, along with soil evaporation and transpiration. Canopy interception is a function of precipitation and LAI.
EMBED Equation.3 (7)
where ndays = number of days in a month, prec = precipitation, and kext = biome-dependent extinction coefficient. The energy flux associated with this term is subtracted from the net radiation in the evapotranspiration computation. This term can be thought of as something like a product of the number of rain events nrain ~ {ndays x (1-exp(-0.005 prec))}, the probability of a raindrop hitting a leaf pint ~ {1.0-exp(kext x LAI)}, and the total evaporative capacity of the canopy per rainfall event eint ~ (0.1 x LAI). Thus, a wet region with 100 mm month-1 of rain (nrain ~12) and an LAI of 4 (pint ~ 0.9, eint ~ 0.4) would intercept ~ 4 mm month-1. A more thorough treatment (many exist) would consider the evaporative demand of the atmosphere and would track the stock of leaf-surface water explicitly, but we lack the temporal resolution (in data and other model equations) to perform such calculations. Parameters in the equation, especially the 0.1, could be modified to attempt to better fit data.
Day-Night disaggregation: Energy fluxes and photosynthesis are computed separately for day and night. This requires use of a diurnal temperature range dataset, and calculation of day and night temperature, vapor pressure deficit, and longwave radiation.
Photosynthesis Detailed description is in Felzer et al. ADDIN EN.CITE Felzer2009127[2009]12712717Felzer, B. S.Cronin, T. W.Melillo, J. M.Kicklighter, D. W.Schlosser, C. A.Importance of carbon-nitrogen interactions and ozone on ecosystem hydrology during the 21st centuryJGR-BiogeosciencesJGR-Biogeosciences114Journal Article2009[HYPERLINK \l "_ENREF_7" \o "Felzer, 2009 #127"2009]. The temperature term, fT, now uses the daytime temperature. The canopy conductance, based on Ball et al. ADDIN EN.CITE Ball198724[1987]242417Ball, J. T.Woodrow, I. E.Berry, J. A.A model predicting stomatal conductance and its contribution to the control of photosynthesis under different environmental conditionsProgress in Photosynthesis ResearchProgress in Photosynthesis ResearchISBN9024734533IVJournal Article1987[HYPERLINK \l "_ENREF_2" \o "Ball, 1987 #24"1987] and the related internal CO2, is now a function of relative humidity rather than a hyperbolic function of vapor pressure deficit, so that is now calculated from using daytime temperature. The photosynthetically active radiation (PAR) is an average daytime value.
Canopy Conductance As detailed above, the moisture dependency is based on relative humidity, which is calculated from vapor pressure and daytime and nighttime temperature.
Evapotranspiration Evapotranspiration is calculated using the Shuttleworth and Wallace ADDIN EN.CITE Shuttleworth1985860[1985]86086017Shuttleworth, W. J.Wallace, J. S.Evaporation from sparse crops: an energy combination theoryQuarterly Journal of the Royal Meteorological Society839-8551111985[HYPERLINK \l "_ENREF_10" \o "Shuttleworth, 1985 #860"1985] approach. Terms that now include day and night differentiation include net radiation, including soil and snow storage, the rate of change of vapor pressure with temperature ( b) , w h i c h d e p e n d s u p o n b o t h t e m p e r a t u r e a n d v a p o r p r e s s u r e d e f i c i t , a n d v a p o r p r e s s u r e d e f i c i t i t s e l f . D a y t i m e a n d n i g h t t i m e t e m p e r a t u r e a n d v a p o r p r e s s u r e d e f i c i t ( c a l c u l a t e d f r o m t h e v a p o r p r e s s u r e s a n d r e s p e c t i v e t e m p e r a t u r e s ) a r e u s e d . I n a d d i t i o n , e mitted longwave radiation is subtracted from the net radiation term (rn) and from the soil radiation (rnsoil), and that is based upon daytime and nighttime temperature according to the Stefan-Boltzmann Law.
EMBED Equation.3
EMBED Equation.3
where vpr = vapor pressure, T = temperature in K, s = S t e f a n - B o l t z m a n c o n s t a n t , e c a n = e v a p o r a t i o n f r o m c a n o p y i n t e r c e p t i o n i n W / m 2 , e s o i l = s o i l e v a p o r a t i o n i n W / m 2 , a n d c o r = 0 . 2 o r 1 . 0 d e p e n d i n g u p o n h o w s u r f a c e r a d i a t i o n c o m p a r e s t o t o p - o f - a t m o s p h e r e r a d i a t i o n A D D I N E N . C I T E <