"landuse" surface resistance

Maybe, the idea of understanding PY as the permanent wilting point is not so good. The following graph shows that the surface resistance of vegetation initially only increases slowly when the soil moisture starts to sink below this threshold (100 mm).

import numpy
from matplotlib import pyplot
from hydpy.models.evap import *

pyplot.figure(figsize=[6.4, 3.2]).set_layout_engine("tight")
parameterstep()
nmbhru(1000)
hrutype(0)
soil(True)
conifer(False)
derived.moy(0)
surfaceresistance(100.0)
wiltingpoint(100.0)
fieldcapacity(200.0)
factors.soilwater = numpy.linspace(0.0, 150.0, nmbhru.value)
model.calc_landusesurfaceresistance_v1()
pyplot.plot(factors.soilwater.values, factors.landusesurfaceresistance.values)
pyplot.ylim((0.0, 1000.0))
pyplot.xlabel("SoilWater [-]")
pyplot.ylabel("LanduseSurfaceResistance [s/m]")

There is another complication for coniferous forests (not for mixed forests). Only for this kind of vegetation "suboptimal" air temperature and humidity conditions can further reduce surface resistance. Generally, low air humidity results in increased surface resistance. For humid air, decreasing air temperature also results in increased surface resistance. For an infinite air temperature and air humidity at saturation, coniferous forests behave like, for example, deciduous forests.

import numpy
from matplotlib import pyplot
from hydpy.models.evap import *

pyplot.figure(figsize=[6.4, 3.2]).set_layout_engine("tight")
parameterstep()
nmbhru(100)
hrutype(0)
soil(True)
conifer(True)
derived.moy(0)
surfaceresistance(100.0)
wiltingpoint(100.0)
factors.soilwater = 100.0
humidities = numpy.linspace(0.0, 1.0, nmbhru.value)
for t in [-5.0, 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0]:
    factors.airtemperature.values = t
    model.calc_saturationvapourpressure_v1()
    factors.actualvapourpressure = humidities * factors.saturationvapourpressure
    model.calc_landusesurfaceresistance_v1()
    pyplot.plot(
        humidities, factors.landusesurfaceresistance.values, label=f"T = {int(t)} °C"
    )
pyplot.legend(frameon=False)
pyplot.xlabel("relative humidity [-]")
pyplot.ylabel("LanduseSurfaceResistance [s/m]")

Extract a Penman-Monteith submodel from HydPy-L(ARSIM) #111

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