Input (pre-processing)

Time-variable boundary data

With an atmospheric or another time-variable boundary condition, the boundary values come from a table of records, the file ATMOSPH.IN of HYDRUS-1D (Time-Variable Boundary Conditions dialog). Each record holds from the end of the previous record (or the initial time) to its time t.

Columns

Column	Description
t	end time of the record [T]
Prec	precipitation (and irrigation) [L/T]
Evap	potential evaporation [L/T] (with LAI partitioning: potential evapotranspiration; with a variable head/flux top: the code KodTop)
Transp	potential transpiration [L/T] (with LAI partitioning: the leaf area index)
hCritA	absolute value of the minimum pressure head at the surface [L]: below it the surface turns into a head condition and the evaporation is reduced (e.g. 10⁴–10⁵ cm)
rBot, hBot, hTop	bottom flux, bottom head, top head [L/T, L] for variable flux or head conditions
Ttop, Tbot, Ampl	temperatures at the top and the bottom and the amplitude of the daily surface temperature (heat transport) [°C]
cTop k, cBot k	concentrations of solute k at the top and the bottom [M/L³] (with active uptake: cBot of the actively taken-up solute is the potential uptake rate)
xRoot	rooting depth (root growth from the atmospheric data) [L]

➕ Add record adds a copy of the last record one time unit later; Import from text file… reads records from a text or CSV file with at least 8 columns in the order of the table. The plot below the table shows precipitation, potential evaporation and transpiration as step functions.

Options

Option	Description
Daily sinusoidal variation of evaporation/transpiration	Distributes daily rates over the day: 24 % of the mean rate at night and a sine wave during the day Fayer (2000) (theory).
Sinusoidal precipitation within each interval	The precipitation of each record follows a sine wave over its interval.
Snow accumulation and melt	Snow below −2 °C, rain above +2 °C, mixed in between; melt with the degree-day factor [L/T/°C] (Ttop is the air temperature) (snow).
Canopy interception	Interception capacity a · LAI with the interception constant a [L] von Hoyningen-Hüne (1983); Braden (1985).
Partition the potential ET by LAI	The Evap column holds ETp and the Transp column the LAI; Tp = ETp (1 − e^−k·LAI) Ritchie (1972) with the extinction coefficient k (0.463).
Repeat the atmospheric records cyclically	After the last record the table starts again (lBCCycles).

Literature cited in this topic

Braden, H. (1985). Ein Energiehaushalts- und Verdunstungsmodell für Wasser- und Stoffhaushaltsuntersuchungen landwirtschaftlich genutzter Einzugsgebiete. Mitteilungen der Deutschen Bodenkundlichen Gesellschaft 42: 294–299.
Fayer, M. J. (2000). UNSAT-H Version 3.0: Unsaturated Soil Water and Heat Flow Model. Theory, User Manual, and Examples. Report PNNL-13249, Pacific Northwest National Laboratory, Richland, WA.
Ritchie, J. T. (1972). Model for predicting evaporation from a row crop with incomplete cover. Water Resources Research 8(5): 1204–1213. doi:10.1029/WR008i005p01204
von Hoyningen-Hüne, J. (1983). Die Interception des Niederschlags in landwirtschaftlichen Beständen. Schriftenreihe des DVWK 57: 1–53.

All sources: References.