monthlyWB {sharpshootR}

Monthly Water Balances

Description

Perform a monthly water balance by "leaky bucket" model, inspired by code from bucket.sim of hydromad package, as defined in Bai et al., (2009) (model "SMA_S1"). The plant available water-holding storage (soil thickness * awc) is used as the "bucket capacity". All water in excess of this capacity is lumped into a single "surplus" term.

Usage

monthlyWB(
  AWC,
  PPT,
  PET,
  S_init = 1,
  starting_month = 1,
  rep = 1,
  keep_last = FALSE,
  distribute = FALSE,
  method = c("equal", "random", "gaussian"),
  k = 10
)

Arguments

AWC

numeric, available water-holding capacity (mm), typically thickness (mm) * awc (fraction)

PPT

numeric, time-series of monthly PPT (mm), calendar year ordering

PET

numeric, time-series of monthly PET (mm), calendar year ordering

S_init

numeric, initial fraction of AWC filled with water (values 0-1)

starting_month

integer, starting month index, 1=January, 9=September

rep

integer, number of cycles to run water balance

keep_last

logical, keep only the last iteration of the water balance

distribute

logical, distribute monthly data into k divisions within each month

method

method for distributing PPT and PET into k divisions:

• 'equal' divides PPT and PET into k equal amounts

• 'random' divides PPT and PET into random proportions generated via multinominal simulation

• 'gaussian' divides PPT and PET according to a bell-shaped curve centered in the middle of each month

k

integer, number of divisions

Details

See the monthly water balance tutorial for further examples and discussion.

A number of important assumptions are made by this style of water balance modeling:

• the concept of field capacity is built into the specified bucket size

• the influence of aquitards or local terrain cannot be integrated into this model

• interception is not used in this model

Value

a data.frame with the following elements:

• PPT: monthly PPT (mm)

• PET: monthly PET (mm)

• U: monthly surplus (mm)

• S: monthly soil moisture storage (mm)

• ET: monthly AET (mm)

• D: monthly deficit (mm)

• month: month number

• mo: month label

References

Arkley R, Ulrich R. 1962. The use of calculated actual and potential evapotranspiration for estimating potential plant growth. Hilgardia 32(10):443-469.

Bai, Y., T. Wagener, P. Reed (2009). A top-down framework for watershed model evaluation and selection under uncertainty. Environmental Modelling and Software 24(8), pp. 901-916.

Farmer, D., M. Sivapalan, Farmer, D. (2003). Climate, soil and vegetation controls upon the variability of water balance in temperate and semiarid landscapes: downward approach to water balance analysis. Water Resources Research 39(2), p 1035.