Functions to calculate the proportion of crown defoliation due to hydraulic disconnection.

```
hydraulics_proportionDefoliationSigmoid(
psiLeaf,
P50,
slope,
PLC_crit = 0.88,
P50_cv = 10
)
hydraulics_proportionDefoliationWeibull(
psiLeaf,
c,
d,
PLC_crit = 0.88,
P50_cv = 10
)
```

## Arguments

- psiLeaf
Leaf water potential (in MPa).

- P50, slope
Parameters of the Sigmoid function.

- PLC_crit
Critical leaf PLC corresponding to defoliation

- P50_cv
Coefficient of variation (in percent) of leaf P50, to describe the
variability in hydraulic vulnerability across crown leaves.

- c, d
Parameters of the Weibull function.

## Value

The proportion of crown defoliation.

## Details

The functions assume that crowns are made of a population of leaves whose
hydraulic vulnerability (i.e. the water potential corresponding to 50
follows a Gaussian distribution centered on the input P50 and with a known coefficient of variation (`P50_cv`

).
The slope parameter (or the c exponent in the case of a Weibull function) is considered constant.
Leaves are hydraulically disconnected, and shedded, when their embolism rate exceeds a critical value (`PLC_crit`

).

## Author

Hervé Cochard, INRAE

Miquel De Cáceres Ainsa, CREAF