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1 | |||
237 | werner | 2 | #include "global.h" |
3 | #include "watercycle.h" |
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4 | #include "climate.h" |
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5 | #include "resourceunit.h" |
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6 | #include "species.h" |
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239 | werner | 7 | #include "model.h" |
237 | werner | 8 | |
9 | WaterCycle::WaterCycle() |
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10 | { |
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266 | werner | 11 | mSoilDepth = 0; |
237 | werner | 12 | } |
13 | |||
239 | werner | 14 | void WaterCycle::setup(const ResourceUnit *ru) |
237 | werner | 15 | { |
16 | mRU = ru; |
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17 | // get values... |
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266 | werner | 18 | mFieldCapacity = 0.; // on top |
281 | werner | 19 | const XmlHelper &xml=GlobalSettings::instance()->settings(); |
20 | mSoilDepth = xml.valueDouble("model.site.soilDepth", 0.) * 10; // convert from cm to mm |
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338 | werner | 21 | double pct_sand = xml.valueDouble("model.site.pctSand"); |
22 | double pct_silt = xml.valueDouble("model.site.pctSilt"); |
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23 | double pct_clay = xml.valueDouble("model.site.pctClay"); |
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24 | if (pct_sand + pct_silt + pct_clay != 100.) |
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25 | throw IException(QString("Setup Watercycle: soil composition percentages do not sum up to 100. Sand: %1, Silt: %2 Clay: %3").arg(pct_sand).arg(pct_silt).arg(pct_clay)); |
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26 | |||
27 | // calculate soil characteristics based on empirical functions (Schwalm & Ek, 2004) |
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28 | // note: the variables are percentages [0..100] |
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29 | mPsi_ref = -exp((1.54 - 0.0095*pct_sand + 0.0063*pct_silt) * log(10)) * 0.000098; // Eq. 83 |
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30 | mPsi_koeff_b = -( 3.1 + 0.157*pct_clay - 0.003*pct_sand ); // Eq. 84 |
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31 | mRho_ref = 0.01 * (50.5 - 0.142*pct_sand - 0.037*pct_clay); // Eq. 78 |
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240 | werner | 32 | mCanopy.setup(); |
339 | werner | 33 | |
34 | mPermanentWiltingPoint = heightFromPsi(-4000); // maximum psi is set to a constant of -4MPa |
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266 | werner | 35 | mFieldCapacity = heightFromPsi(-15); |
36 | mContent = mFieldCapacity; // start with full water content (in the middle of winter) |
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339 | werner | 37 | qDebug() << "setup of water: Psi_ref (kPa)" << mPsi_ref << "Rho_ref" << mRho_ref << "coeff. b" << mPsi_koeff_b; |
237 | werner | 38 | } |
39 | |||
331 | werner | 40 | /** function to calculate the water pressure [saugspannung] for a given amount of water. |
338 | werner | 41 | returns water potential in kPa. |
42 | see http://iland.boku.ac.at/water+cycle#transpiration_and_canopy_conductance */ |
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266 | werner | 43 | inline double WaterCycle::psiFromHeight(const double mm) const |
44 | { |
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45 | // psi_x = psi_ref * ( rho_x / rho_ref) ^ b |
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46 | if (mm<0.001) |
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47 | return -100000000; |
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48 | double psi_x = mPsi_ref * pow((mm / mSoilDepth / mRho_ref),mPsi_koeff_b); |
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338 | werner | 49 | return psi_x; // pis |
266 | werner | 50 | } |
51 | |||
331 | werner | 52 | /// calculate the height of the water column for a given pressure |
338 | werner | 53 | /// return water amount in mm |
54 | /// see http://iland.boku.ac.at/water+cycle#transpiration_and_canopy_conductance |
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266 | werner | 55 | inline double WaterCycle::heightFromPsi(const double psi_kpa) const |
56 | { |
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57 | // rho_x = rho_ref * (psi_x / psi_ref)^(1/b) |
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58 | double h = mSoilDepth * mRho_ref * pow(psi_kpa / mPsi_ref, 1./mPsi_koeff_b); |
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59 | return h; |
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60 | } |
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61 | |||
331 | werner | 62 | /// get canopy characteristics of the resource unit. |
63 | /// It is important, that species-statistics are valid when this function is called (LAI)! |
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237 | werner | 64 | void WaterCycle::getStandValues() |
65 | { |
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246 | werner | 66 | mLAINeedle=mLAIBroadleaved=0.; |
237 | werner | 67 | mCanopyConductance=0.; |
68 | double lai; |
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69 | foreach(const ResourceUnitSpecies &rus, mRU->ruSpecies()) { |
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70 | lai = rus.constStatistics().leafAreaIndex(); |
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71 | if (rus.species()->isConiferous()) |
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72 | mLAINeedle+=lai; |
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73 | else |
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74 | mLAIBroadleaved+=lai; |
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268 | werner | 75 | mCanopyConductance += rus.species()->canopyConductance() * lai; // weigh with LAI |
237 | werner | 76 | } |
77 | double total_lai = mLAIBroadleaved+mLAINeedle; |
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78 | if (total_lai>0.) { |
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79 | mCanopyConductance /= total_lai; |
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268 | werner | 80 | } else { |
81 | mCanopyConductance = 0.02; |
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237 | werner | 82 | } |
240 | werner | 83 | if (total_lai < 3.) { |
237 | werner | 84 | // following Landsberg and Waring: when LAI is < 3, a linear "ramp" from 0 to 3 is assumed |
299 | werner | 85 | // http://iland.boku.ac.at/water+cycle#transpiration_and_canopy_conductance |
237 | werner | 86 | mCanopyConductance *= total_lai / 3.; |
87 | } |
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88 | qDebug() << "WaterCycle:getStandValues: LAI needle" << mLAINeedle << "LAI Broadl:"<< mLAIBroadleaved << "weighted avg. Conductance (m/2):" << mCanopyConductance; |
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89 | } |
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90 | |||
91 | /// Main Water Cycle function. This function triggers all water related tasks for |
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92 | /// one simulation year. |
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299 | werner | 93 | /// @sa http://iland.boku.ac.at/water+cycle |
237 | werner | 94 | void WaterCycle::run() |
95 | { |
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96 | // preparations (once a year) |
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97 | getStandValues(); // fetch canopy characteristics from iLand |
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98 | mCanopy.setStandParameters(mLAINeedle, |
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99 | mLAIBroadleaved, |
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100 | mCanopyConductance); |
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101 | |||
102 | |||
103 | // main loop over all days of the year |
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239 | werner | 104 | double prec_mm, prec_after_interception, prec_to_soil, et, excess; |
338 | werner | 105 | const Climate *climate = mRU->climate(); |
106 | const ClimateDay *day = climate->begin(); |
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107 | const ClimateDay *end = climate->end(); |
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237 | werner | 108 | int doy=0; |
109 | double total_excess = 0.; |
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110 | for (; day<end; ++day, ++doy) { |
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111 | // (1) precipitation of the day |
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112 | prec_mm = day->preciptitation; |
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113 | // (2) interception by the crown |
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114 | prec_after_interception = mCanopy.flow(prec_mm, day->temperature); |
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115 | // (3) storage in the snow pack |
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116 | prec_to_soil = mSnowPack.flow(prec_after_interception, day->temperature); |
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117 | // (4) add rest to soil |
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118 | mContent += prec_to_soil; |
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266 | werner | 119 | |
120 | excess = 0.; |
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121 | if (mContent>mFieldCapacity) { |
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122 | // excess water runoff |
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123 | excess = mContent - mFieldCapacity; |
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124 | total_excess += excess; |
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125 | mContent = mFieldCapacity; |
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126 | } |
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127 | |||
237 | werner | 128 | // calculate the relative water content |
255 | werner | 129 | mRelativeContent[doy] = currentRelContent(); |
266 | werner | 130 | mPsi[doy] = psiFromHeight(mContent); |
335 | werner | 131 | // (5) transpiration of the vegetation (and of water intercepted in canopy) |
338 | werner | 132 | et = mCanopy.evapotranspiration3PG(day, climate->daylength_h(doy)); |
238 | werner | 133 | |
241 | werner | 134 | mContent -= et; // reduce content (transpiration) |
338 | werner | 135 | // add intercepted water (that is *not* evaporated) again to the soil (or add to snow if temp too low -> call to snowpack) |
136 | mContent += mSnowPack.add(mCanopy.interception(),day->temperature); |
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241 | werner | 137 | |
338 | werner | 138 | // do not remove water below the PWP (fixed value) |
266 | werner | 139 | if (mContent<mPermanentWiltingPoint) { |
271 | werner | 140 | et -= mPermanentWiltingPoint - mContent; // reduce et (for bookkeeping) |
266 | werner | 141 | mContent = mPermanentWiltingPoint; |
237 | werner | 142 | } |
266 | werner | 143 | |
271 | werner | 144 | //DBGMODE( |
239 | werner | 145 | if (GlobalSettings::instance()->isDebugEnabled(GlobalSettings::dWaterCycle)) { |
240 | werner | 146 | DebugList &out = GlobalSettings::instance()->debugList(day->id(), GlobalSettings::dWaterCycle); |
239 | werner | 147 | // climatic variables |
364 | werner | 148 | out << day->id() << mRU->index() << day->temperature << day->vpd << day->preciptitation << day->radiation; |
239 | werner | 149 | // fluxes |
271 | werner | 150 | out << prec_after_interception << prec_to_soil << et << mCanopy.evaporationCanopy() |
151 | << mRelativeContent[doy]*mSoilDepth << mPsi[doy] << excess; |
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239 | werner | 152 | // other states |
153 | out << mSnowPack.snowPack(); |
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364 | werner | 154 | //special sanity check: |
155 | if (prec_to_soil>0. && mCanopy.interception()>0.) |
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156 | if (mSnowPack.snowPack()==0. && day->preciptitation==0) |
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157 | qDebug() << "watercontent increase without precipititaion"; |
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239 | werner | 158 | |
159 | } |
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271 | werner | 160 | //); // DBGMODE() |
239 | werner | 161 | |
237 | werner | 162 | } |
163 | } |
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164 | |||
165 | |||
166 | namespace Water { |
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167 | |||
168 | /** calculates the input/output of water that is stored in the snow pack. |
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169 | The approach is similar to Picus 1.3 and ForestBGC (Running, 1988). |
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170 | Returns the amount of water that exits the snowpack (precipitation, snow melt) */ |
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171 | double SnowPack::flow(const double &preciptitation_mm, const double &temperature) |
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172 | { |
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173 | if (temperature>0.) { |
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174 | if (mSnowPack==0.) |
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175 | return preciptitation_mm; // no change |
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176 | else { |
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177 | // snow melts |
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178 | const double melting_coefficient = 0.7; // mm/°C |
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240 | werner | 179 | double melt = qMin(temperature * melting_coefficient, mSnowPack); |
180 | mSnowPack -=melt; |
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237 | werner | 181 | return preciptitation_mm + melt; |
182 | } |
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183 | } else { |
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184 | // snow: |
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185 | mSnowPack += preciptitation_mm; |
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186 | return 0.; // no output. |
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187 | } |
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188 | |||
189 | } |
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190 | |||
191 | |||
334 | werner | 192 | inline double SnowPack::add(const double &preciptitation_mm, const double &temperature) |
193 | { |
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194 | // do nothing for temps > 0° |
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195 | if (temperature>0.) |
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196 | return preciptitation_mm; |
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197 | |||
198 | // temps < 0°: add to snow |
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199 | mSnowPack += preciptitation_mm; |
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200 | return 0.; |
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201 | } |
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202 | |||
237 | werner | 203 | /** Interception in crown canopy. |
204 | Calculates the amount of preciptitation that does not reach the ground and |
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205 | is stored in the canopy. The approach is adopted from Picus 1.3. |
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299 | werner | 206 | Returns the amount of precipitation (mm) that surpasses the canopy layer. |
207 | @sa http://iland.boku.ac.at/water+cycle#precipitation_and_interception */ |
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237 | werner | 208 | double Canopy::flow(const double &preciptitation_mm, const double &temperature) |
209 | { |
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210 | // sanity checks |
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211 | mInterception = 0.; |
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271 | werner | 212 | mEvaporation = 0.; |
237 | werner | 213 | if (!mLAI) |
214 | return preciptitation_mm; |
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215 | if (!preciptitation_mm) |
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216 | return 0.; |
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217 | double max_interception_mm=0.; // maximum interception based on the current foliage |
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218 | double max_storage_mm=0.; // maximum storage in canopy |
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219 | |||
220 | if (mLAINeedle>0.) { |
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221 | // (1) calculate maximum fraction of thru-flow the crown (based on precipitation) |
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222 | double max_flow_needle = 0.9 * sqrt(1.03 - exp(-0.055*preciptitation_mm)); |
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223 | max_interception_mm += preciptitation_mm * (1. - max_flow_needle * mLAINeedle/mLAI); |
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224 | // (2) calculate maximum storage potential based on the current LAI |
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225 | double max_storage_needle = 4. * (1. - exp(-0.55*mLAINeedle) ); |
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226 | max_storage_mm += max_storage_needle; |
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227 | } |
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228 | |||
229 | if (mLAIBroadleaved>0.) { |
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230 | // (1) calculate maximum fraction of thru-flow the crown (based on precipitation) |
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299 | werner | 231 | double max_flow_broad = 0.9 * pow(1.22 - exp(-0.055*preciptitation_mm), 0.35); |
237 | werner | 232 | max_interception_mm += preciptitation_mm * (1. - max_flow_broad * mLAIBroadleaved/mLAI); |
233 | // (2) calculate maximum storage potential based on the current LAI |
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299 | werner | 234 | double max_storage_broad = 2. * (1. - exp(-0.5*mLAIBroadleaved) ); |
237 | werner | 235 | max_storage_mm += max_storage_broad; |
236 | } |
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237 | |||
238 | // (3) calculate actual interception and store for evaporation calculation |
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239 | mInterception = qMin( max_storage_mm, max_interception_mm ); |
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240 | |||
335 | werner | 241 | // (4) limit interception with amount of precipitation |
242 | mInterception = qMin( mInterception, preciptitation_mm); |
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243 | |||
244 | // (5) reduce preciptitaion by the amount that is intercepted by the canopy |
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237 | werner | 245 | return preciptitation_mm - mInterception; |
246 | |||
247 | } |
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248 | |||
239 | werner | 249 | /// sets up the canopy. fetch some global parameter values... |
250 | void Canopy::setup() |
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237 | werner | 251 | { |
240 | werner | 252 | mHeatCapacityAir = Model::settings().heatCapacityAir; // J/kg/°C |
253 | mAirDensity = Model::settings().airDensity; // kg / m3 |
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254 | double airPressure = Model::settings().airPressure; // mbar |
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255 | double heat_capacity_kJ = mHeatCapacityAir / 1000; // convert to: kJ/kg/°C |
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256 | const double latent_heat_water = 2450;// kJ/kg |
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257 | // calc psychrometric constant (in mbar/°C): see also http://en.wikipedia.org/wiki/Psychrometric_constant |
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258 | mPsychrometricConstant = heat_capacity_kJ*airPressure/latent_heat_water/0.622; |
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237 | werner | 259 | } |
260 | |||
261 | void Canopy::setStandParameters(const double LAIneedle, const double LAIbroadleave, const double maxCanopyConductance) |
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262 | { |
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263 | mLAINeedle = LAIneedle; |
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264 | mLAIBroadleaved=LAIbroadleave; |
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265 | mLAI=LAIneedle+LAIbroadleave; |
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239 | werner | 266 | mAvgMaxCanopyConductance = maxCanopyConductance; |
237 | werner | 267 | } |
268 | |||
269 | /** calculate the daily evaporation/transpiration using the Penman-Monteith-Equation. |
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270 | The application of the equation follows broadly Running (1988). |
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271 | Returns the total sum of evaporation+transpiration in mm of the day. */ |
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256 | werner | 272 | double Canopy::evapotranspirationBGC(const ClimateDay *climate, const double daylength_h) |
237 | werner | 273 | { |
238 | werner | 274 | double vpd_mbar = climate->vpd * 10.; // convert from kPa to mbar |
275 | double temperature = climate->temperature; // average temperature of the day (°C) |
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276 | double daylength = daylength_h * 3600.; // daylength in seconds (convert from length in hours) |
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277 | double rad = climate->radiation / daylength * 1000000; //convert from MJ/m2 (day sum) to average radiation flow W/m2 [MJ=MWs -> /s * 1,000,000 |
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237 | werner | 278 | const double aerodynamic_resistance = 5.; // m/s: aerodynamic resistance of the canopy is considered being constant |
279 | const double latent_heat = 2257000.; // Latent heat of vaporization. Energy required per unit mass of water vaporized [J kg-1] |
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280 | |||
281 | // (1) calculate some intermediaries |
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282 | // current canopy conductance: is calculated following Landsberg & Waring |
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240 | werner | 283 | // note: here we use vpd again in kPa. |
237 | werner | 284 | double current_canopy_conductance; |
240 | werner | 285 | current_canopy_conductance = mAvgMaxCanopyConductance * exp(-2.5 * climate->vpd); |
237 | werner | 286 | |
240 | werner | 287 | // saturation vapor pressure (Running 1988, Eq. 1) in mbar |
237 | werner | 288 | double svp = 6.1078 * exp((17.269 * temperature) / (237.3 + temperature) ); |
289 | // the slope of svp is, thanks to http://www.wolframalpha.com/input/?i=derive+y%3D6.1078+exp+((17.269x)/(237.3%2Bx)) |
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290 | double svp_slope = svp * ( 17.269/(237.3+temperature) - 17.269*temperature/((237.3+temperature)*(237.3+temperature)) ); |
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291 | |||
239 | werner | 292 | double et; // transpiration in mm (follows Eq.(8) of Running, 1988). |
293 | // note: RC (resistance of canopy) = 1/CC (conductance of canopy) |
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240 | werner | 294 | double dim = svp_slope + mPsychrometricConstant*(1. + 1. / (current_canopy_conductance*aerodynamic_resistance)); |
246 | werner | 295 | double dayl = daylength*mLAI / latent_heat; |
238 | werner | 296 | double upper = svp_slope*rad + mHeatCapacityAir*mAirDensity * vpd_mbar/aerodynamic_resistance; |
297 | et = upper / dim * dayl; |
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239 | werner | 298 | |
299 | // now calculate the evaporation from intercepted preciptitaion in the canopy: 1+rc/ra -> 1 |
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300 | if (mInterception>0.) { |
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271 | werner | 301 | double dim_evap = svp_slope + mPsychrometricConstant; |
302 | double pot_evap = upper / dim_evap * dayl; |
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303 | double evap = qMin(pot_evap, mInterception); |
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335 | werner | 304 | mInterception -= evap; // reduce interception |
271 | werner | 305 | mEvaporation = evap; |
239 | werner | 306 | } |
237 | werner | 307 | return et; |
308 | } |
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309 | |||
310 | |||
256 | werner | 311 | /** calculate the daily evaporation/transpiration using the Penman-Monteith-Equation. |
312 | This version is based on 3PG. See the Visual Basic Code in 3PGjs.xls. |
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313 | Returns the total sum of evaporation+transpiration in mm of the day. */ |
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314 | double Canopy::evapotranspiration3PG(const ClimateDay *climate, const double daylength_h) |
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315 | { |
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316 | double vpd_mbar = climate->vpd * 10.; // convert from kPa to mbar |
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317 | double temperature = climate->temperature; // average temperature of the day (°C) |
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318 | double daylength = daylength_h * 3600.; // daylength in seconds (convert from length in hours) |
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319 | double rad = climate->radiation / daylength * 1000000; //convert from MJ/m2 (day sum) to average radiation flow W/m2 [MJ=MWs -> /s * 1,000,000 |
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320 | |||
321 | //: Landsberg original: const double e20 = 2.2; //rate of change of saturated VP with T at 20C |
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322 | const double VPDconv = 0.000622; //convert VPD to saturation deficit = 18/29/1000 |
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323 | const double latent_heat = 2460000.; // Latent heat of vaporization. Energy required per unit mass of water vaporized [J kg-1] |
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324 | |||
325 | double gBL = 0.2; // boundary layer conductance |
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326 | // canopy conductance scales linearly from 0 to LAI=3 and is constant for LAI > 3. |
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327 | double gC = mAvgMaxCanopyConductance * exp(-2.5 * climate->vpd); |
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328 | if (mLAI<3.) |
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329 | gC *= mLAI / 3.; |
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330 | |||
331 | double defTerm = mAirDensity * latent_heat * (vpd_mbar * VPDconv) * gBL; |
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332 | // saturation vapor pressure (Running 1988, Eq. 1) in mbar |
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333 | double svp = 6.1078 * exp((17.269 * temperature) / (237.3 + temperature) ); |
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334 | // the slope of svp is, thanks to http://www.wolframalpha.com/input/?i=derive+y%3D6.1078+exp+((17.269x)/(237.3%2Bx)) |
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335 | double svp_slope = svp * ( 17.269/(237.3+temperature) - 17.269*temperature/((237.3+temperature)*(237.3+temperature)) ); |
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336 | |||
337 | double div = (1. + svp_slope + gBL / gC); |
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338 | double Etransp = (svp_slope * rad + defTerm) / div; |
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335 | werner | 339 | double canopy_transpiration = Etransp / latent_heat * daylength; |
256 | werner | 340 | |
341 | if (mInterception>0.) { |
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342 | // we assume that for evaporation from leaf surface gBL/gC -> 0 |
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343 | double div_evap = 1 + svp_slope; |
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344 | double evap = (svp_slope*rad + defTerm) / div_evap / latent_heat * daylength; |
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345 | evap = qMin(evap, mInterception); |
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335 | werner | 346 | mInterception -= evap; // reduce interception |
347 | mEvaporation = evap; // evaporation from intercepted water |
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256 | werner | 348 | } |
335 | werner | 349 | return canopy_transpiration; |
256 | werner | 350 | } |
351 | |||
237 | werner | 352 | } // end namespace |