ModelId:

biome1

SimileVersion:

5.9

This is closely based on the Prentice and ... Biome model, which aims to model the response of vegetation dynamics to climate change under conditions of water strees. The vegetation does not include any state variables (compartments). This is because the response is assessed in terms of net primary productivity (Pnet), rather than in terms of the consequent accumulation of biomass.

Equations:

Equations in Desktopvariable: D = graph(month) variable: month = fmod(time(1),12) variable: bare = 1-sum([f]) variable: total_transp1 = sum([transp1]) variable: total_transp2 = sum([transp2])Equations in VEGETATION TYPEvariable: Aa = ap*phi_d*phi_t Units must be mol(CO2) per month variable: temp = graph(month) variable: a = 0.08 "Ratio of leaf respiration to photosynthetic capacity" (but also (p.653) described as merely "an empirical parameter") variable: sigma = (1-alpha/td)^0.5 "sigma is a dimensionless factor that depends only on the fractional daylength (td) and the ratio of leaf respiration to photosynthetic capacity (alpha)" variable: Ap = fpar*sigma*phi*im "Ap = monthly potential photosynthesis" Units must be mol(CO2) per month variable: FPAR = 0.5 Value??? "fraction of incoming PAR absorbed by the green vegetation" variable: Im = graph(month) Value????? "total monthly incident PAR" Units nust be mol(photons) per month variable: td = 0.5 "fractional daylength" variable: phi = (if temp<13 then 0.07 else(if temp>38 then 0.04 else 0.04+0.03*(temp-13)/(38-13))) "quantum efficiency of gross photosynthesis at prescribed ambient CO2" "mol(CO2)/mol(photons)" "C3 plants at 13C = 0.07, at 38C = 0.04" "C4 plants = 0.054, at any temp" "Field values c. 50% lower" variable: PHI D = e/d "drought scalar, ratio of actual to equilibrium evapotranspiration for the month as calculated by the water flux model" variable: PHI T = (if temp<5 then 0 else(if temp>35 then 0 else(if temp<20 then(temp-5)/(20-5)else(if temp>30 then(temp-30)/(35-30)else 1)))) "monthly temperature scalar, is set to unity across a range of temperatures from T2 to T3. Below T2 the scalar decreases linearly to a value of zero at a temperature T1, and above T3 the scalar decreases to zero at a temperature T4" variable: alpha = z*w1/(z*w1+(1-z)*w2) variable: f = element([1,0,0,0],index(1)) variable: E = min(s,d) Instantaneous evapotranspiration rate, mm/hour. In the paper, this is "integrated analytically over the 24 hour period". In the present model, it is NOT. Need to think about this: can we do numerically, by integrating over the fractiosn of a "typical day" for each month? (i.e. time unit = 1 month, time step = 0.05 'day') variable: transp1 = alpha*f*e variable: beta = (1-z)*w2/(z*w1+(1-z)*w2) variable: transp2 = beta*f*e variable: Z = element([0.33,0.33,0.9,0.9],index(1)) variable: Wr = z*w1+(1-z)*w2 variable: C = 1 mm/hour "maximum possible rate of evapotranspiration by plant species" Value is given in paper. variable: S = c*wr "supply function" for plant species. mm/hour variable: Pnet = aa-0.4*apEquations in WATERcompartment: Water = 100 mm flow: rain = 40 mm/month flow: transpiration = transp+transp2 flow: evaporation = 20*bare variable: W1 = water*thetamax1*d1/(d1+d2) variable: W2 = water*thetamax2*d2/(d1+d2) variable: d1 = 500 mm: depth of upper layer variable: d2 = 1500 mm: depth of lower layer variable: thetamax2 = 200 variable: thetamax1 = 300

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