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Xiaoyan Jiang, Guo-Yue Niu and Zong-Liang YangThe Jackson School of GeosciencesThe University of Texas at Austin

03/20/2007

Feedback between the atmosphere, vegetation and groundwater

represented in WRF/Noah

Offline validation of soil moisture with Illinois data

Coupled WRF/Noah simulations of rainfall in central U.S.

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01/01/98 01/01/99 01/01/00 01/01/01 01/01/02 01/01/03400

500

600

700

800

900

1000Station2

DEFAULT

DVGW

OBSERVATION

01/01/98 01/01/99 01/01/00 01/01/01 01/01/02 01/01/03400

500

600

700

800

900

1000Station12

DEFAULT

DVGW

OBSERVATION

Offline validation of soil moisture with Illinois data(at two stations; daily from 1/1/1998 to 12/31/2002)

• Noah + DVGW produces a much wetter soil than the default Noah.

• DVGW reduces the amplitude of temporal variations.

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IntroductionObjectivesHypothesisLand cover and hydrogeological characteristics

over the Central U.S.Model descriptionExperiment designSimulation results and discussionsConclusions

The Impacts of Vegetation and Groundwater The Impacts of Vegetation and Groundwater Dynamics on North American Warm Season Dynamics on North American Warm Season

Precipitation over the Central U.S.Precipitation over the Central U.S.

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Understand the role of vegetation growth and groundwater dynamics in land-atmosphere interaction.

Improve the prediction of warm season precipitation in a coupled land-atmosphere model.

Identify the high-impact locations (Local or regional?).

Account for the role of initialization in intra-seasonal forecasting through ensemble simulations.

ObjectivesObjectives

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HypothesisRepresenting interactive canopy (or vegetation growth) and groundwater dynamics in a coupled land surface and atmospheric model improves seasonal precipitation.

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Study domain

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Land cover and hydrogeological characteristics over the Central U.S.

Dominant land cover types over the Central U.S. Aquifer distribution from Atlas

8Dickinson, R. E., M. Shaikh, R. Bryant, et al., 1998

Niu, G.-Y., Z.-L. Yang, R.E. Dickinson, L.E. Gulden, and H. Su, 2007

A Coupled Land-Atmosphere Model SystemA Coupled Land-Atmosphere Model System

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Model configurations The version 2.1.2 of the Weather Research and Forecasting model

(WRF) with time-varying sea surface temperatures.

Physics options and input data:• Lin et al. microphysics scheme;• Kain-Fritsch cumulus parameterization scheme;• Yonsei University Planetary boundary layer;• A simple cloud interactive radiation scheme;• Rapid Radiative Transfer Model longwave radiation scheme

A dynamic vegetation model of Dickinson et al. (1998) in Noah LSM. A simple groundwater model (SIMGM) (Niu et al. 2006) in Noah

LSM. NCEP-NARR reanalysis data. The model domain covers the whole continental U.S. and the grid

spacing is 32 km

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Ensemble experiments with WRFEnsemble experiments with WRF

CasesStart from different dates to 8/31/2002

Experimentdescription

DEFAULTPrescribed greenness

fraction

DV

Predicted greenness fraction (or dynamic

vegetation)

DVGWPredicted greenness fraction and water table

depth

05/31 00:0005/31 06:0005/31 12:0005/31 18:0006/01 00:00

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Initial water table level from offline Noah LSM

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Observed and simulated precipitation in June, July and August (JJA) (mm/day)

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Simulated versus observed cumulative precipitation over the Central U.S.

06/10/2002 06/30/2002 07/20/2002 08/09/2002 08/29/20020

50

100

150

200

250

2002(June ~August)

cum

ulat

ive

prec

ipit

atio

n(m

m)

OBSDEFAULTDVDVGW

The performance of DVGW for precipitation is much closer to the observation;DV is also better than DEFAULT.

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Simulated and observed monthly mean precipitation

Monthly precipitation (mm/day)

0

0.5

1

1.5

2

2.5

3

JJA June July August

Obs Default DV DVGW

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Differences of surface temperature between the DV and DEFAULT, DVGW and DV

DV-DEFAULT

DV-DEFAULT

DVGW-DV

DVGW-DV

JJA JJA

July July

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06/10/2002 06/30/2002 07/20/2002 08/09/2002 08/29/2002200

250

300

350

400

450

2002(June~August)

sens

ible

hea

t fl

ux (

W m

-2) DEFAULT

DVDVGW

06/10/2002 06/30/2002 07/20/2002 08/09/2002 08/29/200250

100

150

200

250

300

350

2002(June~August)

late

nt h

eat f

lux

(W m

-2)

DEFAULTDVDVGW

Latent heat flux

Sensible heat flux

DVGW and DV produce higher latent heat flux than DEFAULTover the Central U.S.

DVGW and DV cause less sensible heat flux than DEFAULTover the Central U.S.

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Differences of latent heat flux and precipitationDV-DEFAULT

June

July

August

June

July

August

Latent heat flux Precipitation

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Differences of latent heat flux and precipitationDVGW-DVLatent heat flux Precipitation

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Differences of greenness fraction between DV and DEFAULT; DVGW and DV

DV-DEFAULT DVGW-DV

June August

DV causes higher greenness fraction over most part of the Central U.S.;DVGW further increase the greenness fraction in this area.

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MODIS NDVI-derived and model simulated greenness fraction over the Central U.S.

(in August)

Fg = (NDVIi - NDVImin) / (NDVImax - NDVImin) NDVImin= 0.04 and NDVImax= 0.52

(Gutman and Ignatov 1997)

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Water balance over the Central U.S.in JJA, 2002

Variables Precipitation(mm/day)

Evapotranspiration(mm/day)

Moisture FluxConvergence (mm/day)

NARR 2.3642* 2.9907 -0.4912

DEFAULT 1.2575 2.3181 -0.8660

DV 1.7215 2.9624 -1.0313

DVGW 2.0825 3.1033 -1.2663

GW 1.4614 2.2931 -1.4180

Note: * using CPC observed gauged precipitation

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Diurnal cycle of precipitation

00 03 06 09 12 15 18 21 000.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

(UTC)

Hourly

Pre

cipita

tion(m

m/h

r)

DEFAULTDVDVGWNARR

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Diurnal cycle of Surface Fluxes

00 03 06 09 12 15 18 21 00-50

0

50

100

150

200

250

300

350

400

(UTC)

Sen

sibl

e H

eat F

lux(

W/m

2)

DEFAULT

DV

DVGW

NARR

00 03 06 09 12 15 18 21 000

50

100

150

200

(UTC)

Late

nt H

eat F

lux(

W/m

2)

DEFAULTDVDVGWNARR

00 03 06 09 12 15 18 21 00290

295

300

305

310

315

320

(UTC)

Surf

ace

Tem

per

ature

DEFAULTDVDVGWNARR

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Lifting condensation level as a function of soil moisture index

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ConclusionsConclusions The WRF/Noah model with augmented vegetation and

groundwater dynamics can improve the simulation of summertime precipitation over the Central U.S.

The increased precipitation (by 65%) corresponds to the increased latent heat flux (by 34%).

In summer, precipitation in the Central U.S. mostly comes from local evapotranspiration, showing strong land–atmosphere coupling.

The role of vegetation is significant (by 37%) in the grassland and cropland areas in summer.

Groundwater has impacts (by 16%) on summer precipitation in the transition zone.

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Conclusions (Cont)Conclusions (Cont)

• Throughout the day, precipitation is increased (improved) when vegetation dynamics is included, and it is further increased (improved) when groundwater dynamics is added. These increases are consistent with higher (lower) latent (sensible) heat fluxes.

• The increased precipitation with the Noah enhancements are also consistent with reduced lifting condensation levels, suggesting a positive soil moisture-precipitation feedback (wetter soil, more evapotranspiration, lower lifting condensation levels, and higher rainfall).

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Thanks for your attention!

Questions and suggestions?Questions and suggestions?