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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 | |||
367 | werner | 91 | /// calculate combined VPD and soilwaterresponse for all species |
92 | /// on the RU. This is used for the calc. of the transpiration. |
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93 | inline double WaterCycle::calculateSoilAtmosphereResponse(const double psi_kpa, const double vpd_kpa) |
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94 | { |
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95 | const ResourceUnitSpecies *i; |
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96 | const QVector<ResourceUnitSpecies>::const_iterator iend = mRU->ruSpecies().end(); |
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97 | double min_response; |
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98 | double total_response = 0; |
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99 | for (i=mRU->ruSpecies().begin();i<iend;++i) { |
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100 | if (i->LAIfactor()>0) { |
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101 | i->speciesResponse()->soilAtmosphereResponses(psi_kpa, vpd_kpa, min_response); |
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102 | total_response += min_response * i->LAIfactor(); |
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103 | } |
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104 | } |
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105 | return total_response; |
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106 | } |
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107 | |||
108 | |||
237 | werner | 109 | /// Main Water Cycle function. This function triggers all water related tasks for |
110 | /// one simulation year. |
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299 | werner | 111 | /// @sa http://iland.boku.ac.at/water+cycle |
237 | werner | 112 | void WaterCycle::run() |
113 | { |
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114 | // preparations (once a year) |
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367 | werner | 115 | getStandValues(); // fetch canopy characteristics from iLand (including weighted average for mCanopyConductance) |
237 | werner | 116 | mCanopy.setStandParameters(mLAINeedle, |
117 | mLAIBroadleaved, |
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118 | mCanopyConductance); |
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119 | |||
120 | |||
121 | // main loop over all days of the year |
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239 | werner | 122 | double prec_mm, prec_after_interception, prec_to_soil, et, excess; |
338 | werner | 123 | const Climate *climate = mRU->climate(); |
124 | const ClimateDay *day = climate->begin(); |
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125 | const ClimateDay *end = climate->end(); |
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237 | werner | 126 | int doy=0; |
127 | double total_excess = 0.; |
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128 | for (; day<end; ++day, ++doy) { |
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129 | // (1) precipitation of the day |
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130 | prec_mm = day->preciptitation; |
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131 | // (2) interception by the crown |
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132 | prec_after_interception = mCanopy.flow(prec_mm, day->temperature); |
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133 | // (3) storage in the snow pack |
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134 | prec_to_soil = mSnowPack.flow(prec_after_interception, day->temperature); |
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135 | // (4) add rest to soil |
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136 | mContent += prec_to_soil; |
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266 | werner | 137 | |
138 | excess = 0.; |
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139 | if (mContent>mFieldCapacity) { |
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140 | // excess water runoff |
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141 | excess = mContent - mFieldCapacity; |
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142 | total_excess += excess; |
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143 | mContent = mFieldCapacity; |
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144 | } |
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145 | |||
237 | werner | 146 | // calculate the relative water content |
255 | werner | 147 | mRelativeContent[doy] = currentRelContent(); |
367 | werner | 148 | double current_psi = psiFromHeight(mContent); |
149 | mPsi[doy] = current_psi; |
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335 | werner | 150 | // (5) transpiration of the vegetation (and of water intercepted in canopy) |
367 | werner | 151 | // calculate the LAI-weighted response values for soil water and vpd: |
152 | double combined_response = calculateSoilAtmosphereResponse( current_psi, day->vpd); |
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153 | et = mCanopy.evapotranspiration3PG(day, climate->daylength_h(doy), combined_response); |
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238 | werner | 154 | |
241 | werner | 155 | mContent -= et; // reduce content (transpiration) |
338 | werner | 156 | // add intercepted water (that is *not* evaporated) again to the soil (or add to snow if temp too low -> call to snowpack) |
157 | mContent += mSnowPack.add(mCanopy.interception(),day->temperature); |
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241 | werner | 158 | |
338 | werner | 159 | // do not remove water below the PWP (fixed value) |
266 | werner | 160 | if (mContent<mPermanentWiltingPoint) { |
271 | werner | 161 | et -= mPermanentWiltingPoint - mContent; // reduce et (for bookkeeping) |
266 | werner | 162 | mContent = mPermanentWiltingPoint; |
237 | werner | 163 | } |
266 | werner | 164 | |
271 | werner | 165 | //DBGMODE( |
239 | werner | 166 | if (GlobalSettings::instance()->isDebugEnabled(GlobalSettings::dWaterCycle)) { |
240 | werner | 167 | DebugList &out = GlobalSettings::instance()->debugList(day->id(), GlobalSettings::dWaterCycle); |
239 | werner | 168 | // climatic variables |
364 | werner | 169 | out << day->id() << mRU->index() << day->temperature << day->vpd << day->preciptitation << day->radiation; |
239 | werner | 170 | // fluxes |
271 | werner | 171 | out << prec_after_interception << prec_to_soil << et << mCanopy.evaporationCanopy() |
172 | << mRelativeContent[doy]*mSoilDepth << mPsi[doy] << excess; |
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239 | werner | 173 | // other states |
174 | out << mSnowPack.snowPack(); |
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364 | werner | 175 | //special sanity check: |
176 | if (prec_to_soil>0. && mCanopy.interception()>0.) |
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177 | if (mSnowPack.snowPack()==0. && day->preciptitation==0) |
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178 | qDebug() << "watercontent increase without precipititaion"; |
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239 | werner | 179 | |
180 | } |
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271 | werner | 181 | //); // DBGMODE() |
239 | werner | 182 | |
237 | werner | 183 | } |
184 | } |
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185 | |||
186 | |||
187 | namespace Water { |
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188 | |||
189 | /** calculates the input/output of water that is stored in the snow pack. |
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190 | The approach is similar to Picus 1.3 and ForestBGC (Running, 1988). |
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191 | Returns the amount of water that exits the snowpack (precipitation, snow melt) */ |
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192 | double SnowPack::flow(const double &preciptitation_mm, const double &temperature) |
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193 | { |
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194 | if (temperature>0.) { |
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195 | if (mSnowPack==0.) |
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196 | return preciptitation_mm; // no change |
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197 | else { |
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198 | // snow melts |
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199 | const double melting_coefficient = 0.7; // mm/°C |
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240 | werner | 200 | double melt = qMin(temperature * melting_coefficient, mSnowPack); |
201 | mSnowPack -=melt; |
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237 | werner | 202 | return preciptitation_mm + melt; |
203 | } |
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204 | } else { |
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205 | // snow: |
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206 | mSnowPack += preciptitation_mm; |
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207 | return 0.; // no output. |
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208 | } |
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209 | |||
210 | } |
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211 | |||
212 | |||
334 | werner | 213 | inline double SnowPack::add(const double &preciptitation_mm, const double &temperature) |
214 | { |
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215 | // do nothing for temps > 0° |
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216 | if (temperature>0.) |
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217 | return preciptitation_mm; |
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218 | |||
219 | // temps < 0°: add to snow |
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220 | mSnowPack += preciptitation_mm; |
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221 | return 0.; |
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222 | } |
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223 | |||
237 | werner | 224 | /** Interception in crown canopy. |
225 | Calculates the amount of preciptitation that does not reach the ground and |
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226 | is stored in the canopy. The approach is adopted from Picus 1.3. |
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299 | werner | 227 | Returns the amount of precipitation (mm) that surpasses the canopy layer. |
228 | @sa http://iland.boku.ac.at/water+cycle#precipitation_and_interception */ |
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237 | werner | 229 | double Canopy::flow(const double &preciptitation_mm, const double &temperature) |
230 | { |
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231 | // sanity checks |
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232 | mInterception = 0.; |
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271 | werner | 233 | mEvaporation = 0.; |
237 | werner | 234 | if (!mLAI) |
235 | return preciptitation_mm; |
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236 | if (!preciptitation_mm) |
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237 | return 0.; |
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238 | double max_interception_mm=0.; // maximum interception based on the current foliage |
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239 | double max_storage_mm=0.; // maximum storage in canopy |
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240 | |||
241 | if (mLAINeedle>0.) { |
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242 | // (1) calculate maximum fraction of thru-flow the crown (based on precipitation) |
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243 | double max_flow_needle = 0.9 * sqrt(1.03 - exp(-0.055*preciptitation_mm)); |
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244 | max_interception_mm += preciptitation_mm * (1. - max_flow_needle * mLAINeedle/mLAI); |
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245 | // (2) calculate maximum storage potential based on the current LAI |
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246 | double max_storage_needle = 4. * (1. - exp(-0.55*mLAINeedle) ); |
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247 | max_storage_mm += max_storage_needle; |
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248 | } |
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249 | |||
250 | if (mLAIBroadleaved>0.) { |
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251 | // (1) calculate maximum fraction of thru-flow the crown (based on precipitation) |
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299 | werner | 252 | double max_flow_broad = 0.9 * pow(1.22 - exp(-0.055*preciptitation_mm), 0.35); |
237 | werner | 253 | max_interception_mm += preciptitation_mm * (1. - max_flow_broad * mLAIBroadleaved/mLAI); |
254 | // (2) calculate maximum storage potential based on the current LAI |
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299 | werner | 255 | double max_storage_broad = 2. * (1. - exp(-0.5*mLAIBroadleaved) ); |
237 | werner | 256 | max_storage_mm += max_storage_broad; |
257 | } |
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258 | |||
259 | // (3) calculate actual interception and store for evaporation calculation |
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260 | mInterception = qMin( max_storage_mm, max_interception_mm ); |
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261 | |||
335 | werner | 262 | // (4) limit interception with amount of precipitation |
263 | mInterception = qMin( mInterception, preciptitation_mm); |
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264 | |||
265 | // (5) reduce preciptitaion by the amount that is intercepted by the canopy |
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237 | werner | 266 | return preciptitation_mm - mInterception; |
267 | |||
268 | } |
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269 | |||
239 | werner | 270 | /// sets up the canopy. fetch some global parameter values... |
271 | void Canopy::setup() |
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237 | werner | 272 | { |
240 | werner | 273 | mHeatCapacityAir = Model::settings().heatCapacityAir; // J/kg/°C |
274 | mAirDensity = Model::settings().airDensity; // kg / m3 |
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275 | double airPressure = Model::settings().airPressure; // mbar |
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276 | double heat_capacity_kJ = mHeatCapacityAir / 1000; // convert to: kJ/kg/°C |
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277 | const double latent_heat_water = 2450;// kJ/kg |
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278 | // calc psychrometric constant (in mbar/°C): see also http://en.wikipedia.org/wiki/Psychrometric_constant |
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279 | mPsychrometricConstant = heat_capacity_kJ*airPressure/latent_heat_water/0.622; |
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237 | werner | 280 | } |
281 | |||
282 | void Canopy::setStandParameters(const double LAIneedle, const double LAIbroadleave, const double maxCanopyConductance) |
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283 | { |
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284 | mLAINeedle = LAIneedle; |
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285 | mLAIBroadleaved=LAIbroadleave; |
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286 | mLAI=LAIneedle+LAIbroadleave; |
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239 | werner | 287 | mAvgMaxCanopyConductance = maxCanopyConductance; |
237 | werner | 288 | } |
289 | |||
290 | /** calculate the daily evaporation/transpiration using the Penman-Monteith-Equation. |
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291 | The application of the equation follows broadly Running (1988). |
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292 | Returns the total sum of evaporation+transpiration in mm of the day. */ |
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256 | werner | 293 | double Canopy::evapotranspirationBGC(const ClimateDay *climate, const double daylength_h) |
237 | werner | 294 | { |
238 | werner | 295 | double vpd_mbar = climate->vpd * 10.; // convert from kPa to mbar |
296 | double temperature = climate->temperature; // average temperature of the day (°C) |
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297 | double daylength = daylength_h * 3600.; // daylength in seconds (convert from length in hours) |
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298 | 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 | 299 | const double aerodynamic_resistance = 5.; // m/s: aerodynamic resistance of the canopy is considered being constant |
300 | const double latent_heat = 2257000.; // Latent heat of vaporization. Energy required per unit mass of water vaporized [J kg-1] |
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301 | |||
302 | // (1) calculate some intermediaries |
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303 | // current canopy conductance: is calculated following Landsberg & Waring |
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240 | werner | 304 | // note: here we use vpd again in kPa. |
237 | werner | 305 | double current_canopy_conductance; |
240 | werner | 306 | current_canopy_conductance = mAvgMaxCanopyConductance * exp(-2.5 * climate->vpd); |
237 | werner | 307 | |
240 | werner | 308 | // saturation vapor pressure (Running 1988, Eq. 1) in mbar |
237 | werner | 309 | double svp = 6.1078 * exp((17.269 * temperature) / (237.3 + temperature) ); |
310 | // 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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311 | double svp_slope = svp * ( 17.269/(237.3+temperature) - 17.269*temperature/((237.3+temperature)*(237.3+temperature)) ); |
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312 | |||
239 | werner | 313 | double et; // transpiration in mm (follows Eq.(8) of Running, 1988). |
314 | // note: RC (resistance of canopy) = 1/CC (conductance of canopy) |
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240 | werner | 315 | double dim = svp_slope + mPsychrometricConstant*(1. + 1. / (current_canopy_conductance*aerodynamic_resistance)); |
246 | werner | 316 | double dayl = daylength*mLAI / latent_heat; |
238 | werner | 317 | double upper = svp_slope*rad + mHeatCapacityAir*mAirDensity * vpd_mbar/aerodynamic_resistance; |
318 | et = upper / dim * dayl; |
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239 | werner | 319 | |
320 | // now calculate the evaporation from intercepted preciptitaion in the canopy: 1+rc/ra -> 1 |
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321 | if (mInterception>0.) { |
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271 | werner | 322 | double dim_evap = svp_slope + mPsychrometricConstant; |
323 | double pot_evap = upper / dim_evap * dayl; |
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324 | double evap = qMin(pot_evap, mInterception); |
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335 | werner | 325 | mInterception -= evap; // reduce interception |
271 | werner | 326 | mEvaporation = evap; |
239 | werner | 327 | } |
237 | werner | 328 | return et; |
329 | } |
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330 | |||
331 | |||
256 | werner | 332 | /** calculate the daily evaporation/transpiration using the Penman-Monteith-Equation. |
333 | This version is based on 3PG. See the Visual Basic Code in 3PGjs.xls. |
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334 | Returns the total sum of evaporation+transpiration in mm of the day. */ |
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367 | werner | 335 | double Canopy::evapotranspiration3PG(const ClimateDay *climate, const double daylength_h, const double combined_response) |
256 | werner | 336 | { |
337 | double vpd_mbar = climate->vpd * 10.; // convert from kPa to mbar |
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338 | double temperature = climate->temperature; // average temperature of the day (°C) |
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339 | double daylength = daylength_h * 3600.; // daylength in seconds (convert from length in hours) |
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340 | 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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341 | |||
342 | //: Landsberg original: const double e20 = 2.2; //rate of change of saturated VP with T at 20C |
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343 | const double VPDconv = 0.000622; //convert VPD to saturation deficit = 18/29/1000 |
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344 | const double latent_heat = 2460000.; // Latent heat of vaporization. Energy required per unit mass of water vaporized [J kg-1] |
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345 | |||
346 | double gBL = 0.2; // boundary layer conductance |
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367 | werner | 347 | double gC = mAvgMaxCanopyConductance * combined_response; |
256 | werner | 348 | |
367 | werner | 349 | |
256 | werner | 350 | double defTerm = mAirDensity * latent_heat * (vpd_mbar * VPDconv) * gBL; |
351 | // saturation vapor pressure (Running 1988, Eq. 1) in mbar |
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352 | double svp = 6.1078 * exp((17.269 * temperature) / (237.3 + temperature) ); |
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353 | // 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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354 | double svp_slope = svp * ( 17.269/(237.3+temperature) - 17.269*temperature/((237.3+temperature)*(237.3+temperature)) ); |
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355 | |||
356 | double div = (1. + svp_slope + gBL / gC); |
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357 | double Etransp = (svp_slope * rad + defTerm) / div; |
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335 | werner | 358 | double canopy_transpiration = Etransp / latent_heat * daylength; |
256 | werner | 359 | |
360 | if (mInterception>0.) { |
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361 | // we assume that for evaporation from leaf surface gBL/gC -> 0 |
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362 | double div_evap = 1 + svp_slope; |
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363 | double evap = (svp_slope*rad + defTerm) / div_evap / latent_heat * daylength; |
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364 | evap = qMin(evap, mInterception); |
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335 | werner | 365 | mInterception -= evap; // reduce interception |
366 | mEvaporation = evap; // evaporation from intercepted water |
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256 | werner | 367 | } |
335 | werner | 368 | return canopy_transpiration; |
256 | werner | 369 | } |
370 | |||
237 | werner | 371 | } // end namespace |