calc_SWA_mm: Calculate soil water availability SWA

In DrylandEcology/rSW2metrics: Calculate Ecohydrological Metrics from SOILWAT2 Simulations

Calculate soil water availability SWA

Description

We define available soil water SWA as the amount of soil water SWC that exceeds some base (= critical) amount of soil water SWC_crit[i], i.e.,

SWA[t,i] = max{0, SWC[t,i] - SWC_crit[i]}

for day t and soil layer i.

Usage

calc_SWA_mm(
  sim_swc_daily,
  soils,
  used_depth_range_cm = NULL,
  SWP_limit_MPa = -Inf,
  method = c("across_profile", "by_layer")
)

Arguments

sim_swc_daily	A named list with a "time" element and a "values" element containing daily "swc" for each soil layer in units of centimeters.
soils	A named list with soil parameters "depth_cm", "sand_frac","clay_frac", and "gravel_content" as numeric vectors with values for each soil layer.
used_depth_range_cm	A numeric vector of length two.
SWP_limit_MPa	A numeric value.
method	A character string.

Value

A list with elements "time" and "values" where values represent available soil water in units of millimeters above SWP_limit_MPa: if method is “across_profile”, then summed across used_depth_range_cm, if method is “by_layer”, then columns contain values for each soil layer within used_depth_range_cm.

Details

The base (= critical) amount of soil water SWC_crit[i] is specified via a critical soil water potential SWP_crit, here SWP_limit_MPa, e.g., ⁠SWP_crit = -3.0 MPa⁠. The water release curve employed during the simulation run is used to translate SWP into volumetric water content VWC, i.e.,

VWC_crit[i,matric] = f(SWP_crit, SWRCp[i])

where SWRCp are the parameters describing the water release curve. However, the translation is only valid for the matric soil, i.e., the component without coarse fragments.

SWA in the presence of coarse fragments is calculated as

SWA[t,i] = max{0, SWC[t,i] - w[i] * (1 - cfrag[i]) * VWC_crit[i,matric]}

or equivalently

SWA[t,i] = max{0, w[i] * (1 - cfrag[i]) * (VWC[t,i,matric] - VWC_crit[i,matric])}

where matric volumetric water VWC is multiplied by w[i] * (1 - cfrag[i]) to calculate the amount of water in soil layer i, correcting for the volume occupied by coarse fragments.

For day t, soil layer i, soil layer width w[i], and cfrag[i] = fraction of coarse fragments.

DrylandEcology/rSW2metrics documentation built on May 25, 2023, 10:38 a.m.