Subversion Repositories public iLand

#include "global.h"

#include "watercycle.h"

#include "climate.h"

#include "resourceunit.h"

#include "species.h"

#include "model.h"

WaterCycle::WaterCycle()

{

    mSoilDepth = 0;

    mLastYear = -1;

}

void WaterCycle::setup(const ResourceUnit *ru)

{

    mRU = ru;

    // get values...

    mFieldCapacity = 0.; // on top

    const XmlHelper &xml=GlobalSettings::instance()->settings();

    mSoilDepth = xml.valueDouble("model.site.soilDepth", 0.) * 10; // convert from cm to mm

    double pct_sand = xml.valueDouble("model.site.pctSand");

    double pct_silt = xml.valueDouble("model.site.pctSilt");

    double pct_clay = xml.valueDouble("model.site.pctClay");

    if (pct_sand + pct_silt + pct_clay != 100.)

        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));

    // calculate soil characteristics based on empirical functions (Schwalm & Ek, 2004)

    // note: the variables are percentages [0..100]

    mPsi_ref = -exp((1.54 - 0.0095*pct_sand + 0.0063*pct_silt) * log(10)) * 0.000098; // Eq. 83

    mPsi_koeff_b = -( 3.1 + 0.157*pct_clay - 0.003*pct_sand );  // Eq. 84

    mRho_ref = 0.01 * (50.5 - 0.142*pct_sand - 0.037*pct_clay); // Eq. 78

    mCanopy.setup();

    mPermanentWiltingPoint = heightFromPsi(-4000); // maximum psi is set to a constant of -4MPa

    if (xml.valueBool("model.settings.waterUseSoilSaturation",false)==false) {

        mFieldCapacity = heightFromPsi(-15);

    } else {

        // =-EXP((1.54-0.0095* pctSand +0.0063* pctSilt)*LN(10))*0.000098

        double psi_sat = -exp((1.54-0.0095 * pct_sand + 0.0063*pct_silt)*log(10.))*0.000098;

        mFieldCapacity = heightFromPsi(psi_sat);

        if (logLevelDebug()) qDebug() << "psi: saturation " << psi_sat << "field capacity:" << mFieldCapacity;

    }

    mContent = mFieldCapacity; // start with full water content (in the middle of winter)

    if (logLevelDebug()) qDebug() << "setup of water: Psi_ref (kPa)" << mPsi_ref << "Rho_ref" << mRho_ref << "coeff. b" << mPsi_koeff_b;

    mLastYear = -1;

}

/** function to calculate the water pressure [saugspannung] for a given amount of water.

    returns water potential in kPa.

  see http://iland.boku.ac.at/water+cycle#transpiration_and_canopy_conductance */

inline double WaterCycle::psiFromHeight(const double mm) const

{

    // psi_x = psi_ref * ( rho_x / rho_ref) ^ b

    if (mm<0.001)

        return -100000000;

    double psi_x = mPsi_ref * pow((mm / mSoilDepth / mRho_ref),mPsi_koeff_b);

    return psi_x; // pis

}

/// calculate the height of the water column for a given pressure

/// return water amount in mm

/// see http://iland.boku.ac.at/water+cycle#transpiration_and_canopy_conductance

inline double WaterCycle::heightFromPsi(const double psi_kpa) const

{

    // rho_x = rho_ref * (psi_x / psi_ref)^(1/b)

    double h = mSoilDepth * mRho_ref * pow(psi_kpa / mPsi_ref, 1./mPsi_koeff_b);

    return h;

}

/// get canopy characteristics of the resource unit.

/// It is important, that species-statistics are valid when this function is called (LAI)!

void WaterCycle::getStandValues()

{

    mLAINeedle=mLAIBroadleaved=0.;

    mCanopyConductance=0.;

    const double GroundVegetationCC = 0.02;

    double lai;

    foreach(ResourceUnitSpecies *rus, mRU->ruSpecies()) {

        lai = rus->constStatistics().leafAreaIndex();

        if (rus->species()->isConiferous())

            mLAINeedle+=lai;

        else

            mLAIBroadleaved+=lai;

        mCanopyConductance += rus->species()->canopyConductance() * lai; // weigh with LAI

    }

    double total_lai = mLAIBroadleaved+mLAINeedle;

    // handle cases with LAI < 1 (use generic "ground cover characteristics" instead)

    if (total_lai<1.) {

        mCanopyConductance+=(GroundVegetationCC)*(1. - total_lai);

        total_lai = 1.;

    }

    mCanopyConductance /= total_lai;

    if (total_lai < Model::settings().laiThresholdForClosedStands) {

        // following Landsberg and Waring: when LAI is < 3 (default for laiThresholdForClosedStands), a linear "ramp" from 0 to 3 is assumed

        // http://iland.boku.ac.at/water+cycle#transpiration_and_canopy_conductance

        mCanopyConductance *= total_lai / Model::settings().laiThresholdForClosedStands;

    }

    if (logLevelInfo()) qDebug() << "WaterCycle:getStandValues: LAI needle" << mLAINeedle << "LAI Broadl:"<< mLAIBroadleaved << "weighted avg. Conductance (m/2):" << mCanopyConductance;

}

/// calculate responses for ground vegetation, i.e. for "unstocked" areas.

/// this duplicates calculations done in Species.

/// @return Minimum of vpd and soilwater response for default

inline double WaterCycle::calculateBaseSoilAtmosphereResponse(const double psi_kpa, const double vpd_kpa)

{

    // constant parameters used for ground vegetation:

    const double mPsiMin = 1.5; // MPa

    const double mRespVpdExponent = -0.6;

    // see SpeciesResponse::soilAtmosphereResponses()

    double water_resp;

    // see Species::soilwaterResponse:

    const double psi_mpa = psi_kpa / 1000.; // convert to MPa

    water_resp = limit( 1. - psi_mpa / mPsiMin, 0., 1.);

    // see species::vpdResponse

    double vpd_resp;

    vpd_resp =  exp(mRespVpdExponent * vpd_kpa);

    return qMin(water_resp, vpd_resp);

}

/// calculate combined VPD and soilwaterresponse for all species

/// on the RU. This is used for the calc. of the transpiration.

inline double WaterCycle::calculateSoilAtmosphereResponse(const double psi_kpa, const double vpd_kpa)

{

    double min_response;

    double total_response = 0; // LAI weighted minimum response for all speices on the RU

    double total_lai_factor = 0.;

    foreach(ResourceUnitSpecies *rus, mRU->ruSpecies()) {

        if (rus->LAIfactor()>0) {

            // retrieve the minimum of VPD / soil water response for that species

            rus->speciesResponse()->soilAtmosphereResponses(psi_kpa, vpd_kpa, min_response);

            total_response += min_response * rus->LAIfactor();

            total_lai_factor += rus->LAIfactor();

        }

    }

    if (total_lai_factor<1.) {

        // the LAI is below 1: the rest is considered as "ground vegetation"

        total_response += calculateBaseSoilAtmosphereResponse(psi_kpa, vpd_kpa) * (1. - total_lai_factor);

    }

    // add an aging factor to the total response (averageAging: leaf area weighted mean aging value):

    // conceptually: response = min(vpd_response, water_response)*aging

    if (total_lai_factor==1.)

        total_response *= mRU->averageAging(); // no ground cover: use aging value for all LA

    else if (total_lai_factor>0. && mRU->averageAging()>0.)

        total_response *= (1.-total_lai_factor)*1. + (total_lai_factor * mRU->averageAging()); // between 0..1: a part of the LAI is "ground cover" (aging=1)

    DBGMODE( if (mRU->averageAging()>1. || mRU->averageAging()<0. || total_response<0 || total_response>1.)

        qDebug() << "water cycle: average aging invalid. aging:" << mRU->averageAging() << "total response" << total_response;

    );

    //DBG_IF(mRU->averageAging()>1. || mRU->averageAging()<0.,"water cycle", "average aging invalid!" );

    return total_response;

}

/// Main Water Cycle function. This function triggers all water related tasks for

/// one simulation year.

/// @sa http://iland.boku.ac.at/water+cycle

void WaterCycle::run()

{

    // necessary?

    if (GlobalSettings::instance()->currentYear() == mLastYear)

        return;

    // preparations (once a year)

    getStandValues(); // fetch canopy characteristics from iLand (including weighted average for mCanopyConductance)

    mCanopy.setStandParameters(mLAINeedle,

                               mLAIBroadleaved,

                               mCanopyConductance);

    // main loop over all days of the year

    double prec_mm, prec_after_interception, prec_to_soil, et, excess;

    const Climate *climate = mRU->climate();

    const ClimateDay *day = climate->begin();

    const ClimateDay *end = climate->end();

    int doy=0;

    double total_excess = 0.;

    for (; day<end; ++day, ++doy) {

        // (1) precipitation of the day

        prec_mm = day->preciptitation;

        // (2) interception by the crown

        prec_after_interception = mCanopy.flow(prec_mm, day->temperature);

        // (3) storage in the snow pack

        prec_to_soil = mSnowPack.flow(prec_after_interception, day->temperature);

        // (4) add rest to soil

        mContent += prec_to_soil;

        excess = 0.;

        if (mContent>mFieldCapacity) {

            // excess water runoff

            excess = mContent - mFieldCapacity;

            total_excess += excess;

            mContent = mFieldCapacity;

        }

        double current_psi = psiFromHeight(mContent);

        mPsi[doy] = current_psi;

        mWaterDeficit_mm[doy] = mFieldCapacity - mContent;

        // (5) transpiration of the vegetation (and of water intercepted in canopy)

        // calculate the LAI-weighted response values for soil water and vpd:

        double combined_response = calculateSoilAtmosphereResponse( current_psi, day->vpd);

        et = mCanopy.evapotranspiration3PG(day, climate->daylength_h(doy), combined_response);

        mContent -= et; // reduce content (transpiration)

        // add intercepted water (that is *not* evaporated) again to the soil (or add to snow if temp too low -> call to snowpack)

        mContent += mSnowPack.add(mCanopy.interception(),day->temperature);

        // do not remove water below the PWP (fixed value)

        if (mContent<mPermanentWiltingPoint) {

            et -= mPermanentWiltingPoint - mContent; // reduce et (for bookkeeping)

            mContent = mPermanentWiltingPoint;

        }

        //DBGMODE(

            if (GlobalSettings::instance()->isDebugEnabled(GlobalSettings::dWaterCycle)) {

                DebugList &out = GlobalSettings::instance()->debugList(day->id(), GlobalSettings::dWaterCycle);

                // climatic variables

                out << day->id() << mRU->index() << day->temperature << day->vpd << day->preciptitation << day->radiation;

                out << combined_response; // combined response of all species on RU (min(water, vpd))

                // fluxes

                out << prec_after_interception << prec_to_soil << et << mCanopy.evaporationCanopy()

                        << mContent << mPsi[doy] << excess;

                // other states

                out << mSnowPack.snowPack();

                //special sanity check:

                if (prec_to_soil>0. && mCanopy.interception()>0.)

                    if (mSnowPack.snowPack()==0. && day->preciptitation==0)

                        qDebug() << "watercontent increase without precipititaion";

            }

        //); // DBGMODE()

    }

    mLastYear = GlobalSettings::instance()->currentYear();

}

namespace Water {

/** calculates the input/output of water that is stored in the snow pack.

  The approach is similar to Picus 1.3 and ForestBGC (Running, 1988).

  Returns the amount of water that exits the snowpack (precipitation, snow melt) */

double SnowPack::flow(const double &preciptitation_mm, const double &temperature)

{

    if (temperature>0.) {

        if (mSnowPack==0.)

            return preciptitation_mm; // no change

        else {

            // snow melts

            const double melting_coefficient = 0.7; // mm/°C

            double melt = qMin(temperature * melting_coefficient, mSnowPack);

            mSnowPack -=melt;

            return preciptitation_mm + melt;

        }

    } else {

        // snow:

        mSnowPack += preciptitation_mm;

        return 0.; // no output.

    }

}

inline double SnowPack::add(const double &preciptitation_mm, const double &temperature)

{

    // do nothing for temps > 0°

    if (temperature>0.)

        return preciptitation_mm;

    // temps < 0°: add to snow

    mSnowPack += preciptitation_mm;

    return 0.;

}

/** Interception in crown canopy.

    Calculates the amount of preciptitation that does not reach the ground and

    is stored in the canopy. The approach is adopted from Picus 1.3.

    Returns the amount of precipitation (mm) that surpasses the canopy layer.

    @sa http://iland.boku.ac.at/water+cycle#precipitation_and_interception */

double Canopy::flow(const double &preciptitation_mm, const double &temperature)

{

    // sanity checks

    mInterception = 0.;

    mEvaporation = 0.;

    if (!mLAI)

        return preciptitation_mm;

    if (!preciptitation_mm)

        return 0.;

    double max_interception_mm=0.; // maximum interception based on the current foliage

    double max_storage_mm=0.; // maximum storage in canopy

    if (mLAINeedle>0.) {

        // (1) calculate maximum fraction of thru-flow the crown (based on precipitation)

        double max_flow_needle = 0.9 * sqrt(1.03 - exp(-0.055*preciptitation_mm));

        max_interception_mm += preciptitation_mm *  (1. - max_flow_needle * mLAINeedle/mLAI);

        // (2) calculate maximum storage potential based on the current LAI

        double max_storage_needle = 4. * (1. - exp(-0.55*mLAINeedle) );

        max_storage_mm += max_storage_needle;

    }

    if (mLAIBroadleaved>0.) {

        // (1) calculate maximum fraction of thru-flow the crown (based on precipitation)

        double max_flow_broad = 0.9 * pow(1.22 - exp(-0.055*preciptitation_mm), 0.35);

        max_interception_mm += preciptitation_mm *  (1. - max_flow_broad * mLAIBroadleaved/mLAI);

        // (2) calculate maximum storage potential based on the current LAI

        double max_storage_broad = 2. * (1. - exp(-0.5*mLAIBroadleaved) );

        max_storage_mm += max_storage_broad;

    }

    // (3) calculate actual interception and store for evaporation calculation

    mInterception = qMin( max_storage_mm, max_interception_mm );

    // (4) limit interception with amount of precipitation

    mInterception = qMin( mInterception, preciptitation_mm);

    // (5) reduce preciptitaion by the amount that is intercepted by the canopy

    return preciptitation_mm - mInterception;

}

/// sets up the canopy. fetch some global parameter values...

void Canopy::setup()

{

    mAirDensity = Model::settings().airDensity; // kg / m3

}

void Canopy::setStandParameters(const double LAIneedle, const double LAIbroadleave, const double maxCanopyConductance)

{

    mLAINeedle = LAIneedle;

    mLAIBroadleaved=LAIbroadleave;

    mLAI=LAIneedle+LAIbroadleave;

    mAvgMaxCanopyConductance = maxCanopyConductance;

}

/** calculate the daily evaporation/transpiration using the Penman-Monteith-Equation.

   This version is based on 3PG. See the Visual Basic Code in 3PGjs.xls.

   Returns the total sum of evaporation+transpiration in mm of the day. */

double Canopy::evapotranspiration3PG(const ClimateDay *climate, const double daylength_h, const double combined_response)

{

    double vpd_mbar = climate->vpd * 10.; // convert from kPa to mbar

    double temperature = climate->temperature; // average temperature of the day (°C)

    double daylength = daylength_h * 3600.; // daylength in seconds (convert from length in hours)

    double rad = climate->radiation / daylength * 1000000; //convert from MJ/m2 (day sum) to average radiation flow W/m2 [MJ=MWs -> /s * 1,000,000

    //: Landsberg original: const double e20 = 2.2;  //rate of change of saturated VP with T at 20C

    const double VPDconv = 0.000622; //convert VPD to saturation deficit = 18/29/1000

    const double latent_heat = 2460000.; // Latent heat of vaporization. Energy required per unit mass of water vaporized [J kg-1]

    double gBL  = Model::settings().boundaryLayerConductance; // boundary layer conductance

    // canopy conductance.

    // The species traits are weighted by LAI on the RU.

    // maximum canopy conductance: see getStandValues()

    // current response: see calculateSoilAtmosphereResponse(). This is basically a weighted average of min(water_response, vpd_response) for each species

    double gC = mAvgMaxCanopyConductance * combined_response;

    double defTerm = mAirDensity * latent_heat * (vpd_mbar * VPDconv) * gBL;

        // saturation vapor pressure (Running 1988, Eq. 1) in mbar

    double svp = 6.1078 * exp((17.269 * temperature) / (237.3 + temperature) );

    // the slope of svp is, thanks to http://www.wolframalpha.com/input/?i=derive+y%3D6.1078+exp+((17.269x)/(237.3%2Bx))

    double svp_slope = svp * ( 17.269/(237.3+temperature) - 17.269*temperature/((237.3+temperature)*(237.3+temperature)) );

    double div = (1. + svp_slope + gBL / gC);

    double Etransp = (svp_slope * rad + defTerm) / div;

    double canopy_transpiration = Etransp / latent_heat * daylength;

    if (mInterception>0.) {

        // we assume that for evaporation from leaf surface gBL/gC -> 0

        double div_evap = 1 + svp_slope;

        double evap = (svp_slope*rad + defTerm) / div_evap / latent_heat * daylength;

        evap = qMin(evap, mInterception);

        mInterception -= evap; // reduce interception

        mEvaporation = evap; // evaporation from intercepted water

    }

    return canopy_transpiration;

}

} // end namespace