VIC Model StatusBlowing Snow and Lake Algorithms

Princeton MeetingDecember 4, 2006

Blowing Snow

Günter Eisenhardt 3.31.2002, Iceland

Predictive model of the sublimation from blowing snow

SWE > 0?Snow mass

and energy balance

Snowaccumulation

YesBlowingsnow

sublimation

No

ee QMP

dt

dW

vQp

eve QQpMP

dt

dW

• Derived from existing small-scale blowing snow models (Pomeroy et al. 1993 and Liston and Sturm 1998).

• Mass concentration of suspended transport based on power law relationship (Kind 1992).

•Particle sublimation rate proportional to the undersaturation of water vapor.

= VIC snow model

Distribution of terrain slopes

Trail Valley Creek, NWT Imnavait Creek, Alaska

Non-equilibrium Transport

average fetch, f

transport = 0

transport = Qt(x= f)

snow

Simulated annual sublimation from blowing snowSensitivity to fetch

Permafrost and frozen ground

• Soil node temperatures solved via heat diffusion equation (Cherkauer and Lettenmaier 1999)

• Constant flux or constant temperature options

• Imposed temperature distribution at each node allows spatial variation of infiltration capacity and active layer depth across the grid cell (Cherkauer et al. 2001)

Imnavait Creek active layer depth

Betty Pingo SWE and active layer depth

On-going work at UW

• Confirmed functionality of constant flux solution

• Revise distribution of soil thermal nodes to improve stability

• Introduce ground ice parameterization

Lakes and wetlands

Source: San Diego State University Global Change Research Group

Predicting the effects of lakes and wetlands

• Lake energy balance based on:– Hostetler and Bartlein

(1990)

– Hostetler (1991)

• Lake ice cover (Patterson and Hamblein)

• Assumptions:– One “effective” lake for

each grid cell;

– Laterally-averaged temperatures.

Lake energy balance

Lake surface energy balance

Mean daily values, June-August 2000

Mean diurnal values, June-August 2000‘Lake 1’, Arctic

Coastal Plain, Alaska

Observed

Simulated

Mean temperature profile (1993-1997)Toolik Lake, Alaska

Wetland Algorithm

soilsaturated

land surface runoff &

baseflow enters lake

evaporation depletes soil

moisture

lake recharges

soil moisture

Simulated saturated extentPutuligayuk River, Alaska

History

• Original model - documented (briefly) in Cherkauer et al. (2003)

• Subsequent revisions (incorporated into VIC 4.1.0 r3 and documented in Bowling et al. manuscript):– Lakes can disappear/reappear– Lake profile description and thermal

solution nodes separated– Lake runoff rate more physically described

Current Efforts

Water Table

Previously VIC did not calculate the water table depthAverage depth to water table calculated for each vegetation type Summation of depth of saturated layers and depth of excess soil moisture for unsaturated layer

Upland fraction

(variable)Lake fraction

(variable)

Wetland fraction (const)

h

lake

Upland fraction

(variable)Lake fraction

(variable)

Wetland fraction (const)

h

lake

VIC Simulations

VIC top layer moistureVIC 2nd layer moistureVIC water table

Observations

• Observations show rain pulse penetrating to water table quickly

• Issue of moisture transfer to depth?

or• Lateral inflow

from flooded ditch?

Lateral Exchange

Previously the lake could not recharge the local groundwaterEquilibrium soil moisture is calculated to determine flow directionBaseflow can go either into or out of the lake in a given time step

Baseflow out of lake is at maximum rate

h

lake lake

Equilibrium Soil Moisture Soil Moisture State

Lake Extent

Previously, maximum water extent fixed by inputs elevation curve supplied for this

wetland fraction only emerging land had static

characteristics never worked with snow bands

Wetland now considered a subset of each vegetation type Same elevation curve applies to all

vegetation classes? Lake area can be calculated

separately for each veg class, or collapsed back to one effective lake

Could be a nightmare to calibrate

Lake extent scenarios

• Three scenarios defined:1) Variable extent/defined

maximum, e.g. as defined by Bowling et al. (2002)

2) Constant extent, as used by Su et al. (2005)

3) Variable extent/unlimited growth

• Maximum depth adjusted such that scenarios 1 and 2 have equal volume

Grid CellFractional Area

Fra

ctio

nal D

epth

Change in open water extent

Scenario 1 Scenario 2 Scenario 3

Sub-Lake Energy Exchange

Previously, heat fluxes in the soil below the lake were not resolved Normal VIC implementation for

exposed wetland soil (these are values output)

Appropriate soil heat flux algorithm called for sub-lake soil Assumes that soil layers are

preserved under the lake When lake reaches a threshold depth,

energy balance must be solved for combined water/soil layer for stability

What else?

• Photosynthesis – based ET scheme?

• Groundwater parameterization• Permafrost runoff scheme