Model help:TopoFlow-Evaporation-Priestley Taylor

The CSDMS Help System

TopoFlow-Evaporation-Priestley Taylor

This module is the evaporation process component (Priestley-Taylor method) for a D8-based, spatial hydrologic model.

Model introduction

This process component is part of a spatially-distributed hydrologic model called TopoFlow, but it can now be used as a stand-alone model.

Model parameters

Parameter	Description	Unit
Component status	Enabled / Disabled	[-]
Input directory	The location of the input files	[-]
Output directory	The location for the output files	[-]
Site prefix		[-]
Case prefix		[-]
Number of steps	Number of simulation steps	[-]
Time step		[sec]
alpha type	Allowed input types: Scalar / Grid /Time_Series /Grid_Sequence	[-]
alpha	coefficient	[-]
K_soil type	Allowed input types: Scalar / Grid /Time_Series /Grid_Sequence	[-]
K_soil	thermal conductivity of soil	[W / m / deg_C]
soil_x type	Allowed input types: Scalar / Grid /Time_Series /Grid_Sequence	[-]
soil_x	reference depth in soil	[m]
T_soil_x type	Allowed input types: Scalar / Grid /Time_Series /Grid_Sequence	[-]
T_soil_x	temperature of soil at depth x	[deg_C]

Parameter	Description	Unit
Save grid timestep	time interval between saved grids	[sec]
Save er grids toggle	option to save grids of evap. rate	[mm / hr]
Save er grids file	file name for grid stack of evap. rate	[mm / hr]
Save pixels timestep	time interval between time series values	[sec]
Save er pixels toggle	option to save time series of evap. rate	[-]
Save er pixels file	file name for time series of evap. rate	[mm / hr]

Uses ports

• Meteorology
• Channels (surface water flow in a network of channels with trapezoidal cross-section)
• Snow (Snowmelt)
• Infil (Infiltration)
• Satzone (Subsurface flow in saturated zone)

Provides ports

• Evap (Evaporation)
• Configure (tabbed dialog GUI to change settings)
• Run (only if used as the Driver)

Main equations

Evaporation rate

<math>ET=\left (1000 \ast Q_{et}\right) / \left (\rho_{water} \ast L_{v}\right) </math>

(1)

Energy flux used to evaporate water

<math>Q_{et}= \alpha \ast [ 0.406 + \left ( 0.011 \ast T_{air}\right)] \ast \left ( Q_{SW} + Q_{LW} - Q_{c}\right) </math>

(2)

Conduction energy flux

<math>Q_{c}= K_{soil} \ast \left (T_{soil_x} - T_{surf} \right) \ast \left ( 100 / x \right) </math>

(3)

Nomenclature

Symbol	Description	Unit
Q_SW	net shortwave radiation	[W / m²]
Q_LW	net longwave radiation	[W / m²]
T_air	air temperature	deg C
T_surf	surface (snow) temperature	deg C
T_{soil_x}	soil temperature at depth x	deg C
x	reference depth in soil	m
K_soil	thermal conductivity of soil	W / (m deg_C )
α	coefficient	-
L_v	latent heat of vaporization, water (2500000)	J /kg
ρ_water	density of water	kg / m³
ET	evaporation rate	mm / sec
Q_et	energy flux used to evaporate water	W / m²
Q_c	conduction energy flux (between surf. and subsurf.)	W / m²
Ri	Rechardson's number	-

Notes

Notes on Input Parameters

For each variable, you may choose from the droplist of data types. For the "Scalar" data type, enter a numeric value with the units indicated in the dialog. For the other data types, enter a filename. Values in files must also use the indicated units.

Single grids and grid sequences are assumed to be stored as RTG and RTS files, respectively. Time series are assumed to be stored as text files, with one value per line. For a time series or grid sequence, the time between values must coincide with the timestep provided.

If net total radiation has been measured, it can be entered as Q_SW and then Q_LW can be set to zero. Any meteorological variables entered here (such as T_air) are automatically shared with other other processes, such as Snowmelt and Precipitation.

Notes on the Equations

All variables and their units can be seen by expanding the Nomenclature section above.

Wherever (d > 0), evaporation results in a reduction in the surface flow depth. Wherever (d = 0), water is removed from subsurface storage. If the 1D Richards' equation is used for infiltration, then the evaporation rate is applied as a surface boundary condition and alters the soil moisture profile accordingly.

Examples

An example run with input parameters, BLD files, as well as a figure / movie of the output

Follow the next steps to include images / movies of simulations:

Upload file: https://csdms.colorado.edu/wiki/Special:Upload
Create link to the file on your page: [[Image:<file name>]].

Developer(s)

Scott Peckham

References

Zhang, Z., D.L. Kane and L.D. Hinzman (2000) Development and application of a spatially-distributed Arctic hydrological and thermal process model (ARHYTHM), Hydrological Processes, 14, 1017-1044.

Links

Related Help Pages

Model Metadata