Soil Dust Emissions
Ina TegenInstitute for Tropospheric Research
Leipzig, Germany

Saharan
Saharan dust
dust stormstorm fromfrom SpaceSpace Shuttle,Shuttle, 1992
1992

BigBig Spring,Spring, TX,TX, 16.6.1997
16.6.1997

Dead
Dead Sea
Sea

Shanton, TX, 13.6.2002

IPCC, 2001:

IPCC, 2001

IPCC, 2001:
Assuming 50% ‘anthropogenic’ dust

IPCC, 2001

Global Dust Indicators
Dust Storm Frequencies, 1970-1990s,(Visibility < 1km)
(International Station Meteorological

Climate Summary (ISMCS) version 4.0)
02

1050

days/yr

Total Ozone Mapping Satellite
Absorbing Aerosol Index(1985-1990)(Engelstaedter et al. 2003)

Global Dust Indicators
Dust Storm Frequencies, 1970-1990s,(Visibility < 1km)
(International Station Meteorological

Climate Summary (ISMCS) version 4.0)021050days/yr

Bias to inhabited regions

Total Ozone Mapping Satellite
Absorbing Aerosol Index(1985-1990)

Dust originating in deserts(Engelstaedter et al. 2003)

Do we understand dust variability
on interannual to decadal
timescales?
- Satellite: Few long-term records, consistency?
- Station data of dust concentration/ice cores:
only sparse information¾ Analysis of dust storm frequency dataDust StormFrequency
Changes inAfrica

N’tchayi Mbourou et al. (1997)

Zhang et al, 2003

Dust Changes
in ChinaDo we understand dust variability
on interannual to decadal
timescales?
- Satellite: Few long-term records, consistency?
- Station data of dust concentration/ice cores:
only sparse information¾ Analysis of dust storm frequency data

¾ Transport models using meteorological fields
from a series of reanalysis years

Processes of Soil Particle Movement(Numbers in brackets indicate typical particle diameters)

Pye (1987)

Dependence of threshold wind
shear for dust emission on z0

Minimum u* required fordust emission
after Marticorena and Bergametti, 1995

after Iversen and White (1982)

Some dust emission schemes
used in global models
Tegen et al., 1994:

F = ∑ (Ci (u − 6.5m / s )u 2 )i

C: Calibration
constantMarticorena et al., 1997
2  uuρ 3 *tri  1 − *tri  si 
F = α u* ∑ 1 +
2  

gu

u
* i * Ginoux et al, 2001

[F = CS ∑ (u − utri (soil moisture))u 2 siiα: depending onsoil type] S: topography
factorfor u>utr (or u*>u*tr)
F: dust flux, u: surface wind speed, utr: threshold wind speed, u* surface wind shear, si:fraction of particles in size bin i, ρ= air density, g: gravitational constant

Usually areas with high vegetation and soil moisture are masked out

Dust source areas: Vegetation mask

Annual dust sources

No dust emission

Seasonal dust sources

Preferential sourceDust Budget Estimates

Zender et al., 2004

Human Impact on Dust Emissions
Impact on soil surfaces by:¾ Cultivation in arid and semi arid regions (+)- (Soil protection, irrigation) (-)¾ Overgrazing (+)¾ Deforestation (+)¾ Unpaved roads, construction (+)¾ Military activities in deserts (+)

Human Impact on Dust Emissions
Impact on soil surfaces by:¾ Cultivation in arid and semi arid regions (+)- (Soil protection, irrigation) (-)¾ Overgrazing (+)¾ Deforestation (+)¾ Unpaved roads, construction (+)¾ Military activities in deserts (+)
Impact on climate:¾ Changes in meteorology (wind, precipitation) (+/-)¾ Changes in natural vegetation (+/-)

Human Impact on Dust Emissions
Impact on soil surfaces by:¾ Anthropogenic Dust of First Kind
1. Direct emission by mechanical impact
2. Wind erosion of disturbed soils
Impact on climate:¾ Anthropogenic Dust of Second Kind
(Zender et al, 2004)

Methods to estimate anthropogenic
contribution from global models:¾Global models: Increase of dustemissions by either enhancing emission
factor or decreasing u*tr in regions withdisturbed soils
2  uuρ 3 *tri *tri  F = α u* ∑ 1 +1 − 2  si
u* gu*  i  Methods to estimate anthropogenic
contribution from global models:¾Global models: Increase of dustemissions by either enhancing emission
factor or decreasing u*tr in regions withdisturbed soils
2  

uu
ρ 3 *tri *tri  F = α u* ∑ 1 +1 − 2  si
u* gu*  i  Human Impact on Dust Emissions
Global estimates of dust fluxes fromanthropogenically disturbed soils:¾ IPCC, 2001: up to 50% (determines radiative forcing)Ö based on model/satellite AOT comparison (ocean)Human Impact on Dust Emissions
Global estimates of dust fluxes fromanthropogenically disturbed soils:¾ IPCC, 2001:

up to 50% (determines radiative forcing)¾ Prospero et al, 2002: small (Natural sources dominant)TOMS absorbing aerosol index 1985-1990¾ “Dust mostly originates from deserts ‘hot spots’ in uncultivatedregions”

Preferential Dust Source Areas

Ginoux et al., 2001

Human Impact on Dust Emissions
Global estimates of dust fluxes fromanthropogenically disturbed soils:¾ IPCC, 2001: up to 50% (determines radiative forcing)¾ Prospero et al, 2002: small (Natural sources dominant)¾ Luo et al., 2003: 0-50% (‘new desert source’)Ö based on comparison of different model scenarioswith concentration data from surface stations

Human Impact on Dust Emissions
Global estimates of dust fluxes fromanthropogenically disturbed soils:¾ IPCC, 2001:

up to 50% (determines radiative forcing)¾ Prospero et al, 2002: small (Natural sources dominant)¾ Luo et al., 2003: 0-50% (‘new desert source’)¾ Yoshioka et al., in press.: <25% (North Africa)
Ö based on comparison of different model
scenarios with TOMS AI

Human Impact on Dust Emissions
Global estimates of dust fluxes fromanthropogenically disturbed soils:¾ IPCC, 2001: up to 50% (determines radiative forcing)¾ Prospero et al, 2002: small (Natural sources dominant)¾ Luo et al., 2003: 0-50% (‘new desert source’)¾ Yoshioka et al., in press.: <25% (North Africa)¾ Tegen et al., 2004: <10% (Agricultural soils)
Ö based on comparison of different model
scenarios with DSF climatology data

Observed differences between dust storm
frequencies in different source regions

Vegetation cover

Tegen et al., 2004

¾Small but significant increase in cultivated areas for locations grouped
according to vegetation cover.

Dust Emissions from Natural andCultivated Soils¾Satellite z0¾ECMWF ERA15¾Year 1987
Natural emission

1800 Mt/yr

Percent dust fromcultivation:• ERA15, const. z0: 7%• ERA15, ERS z0: 6%• NCEP: 8%

100 Mt/yr

Agricultural emission

Human Impact on Dust Emissions
Global estimates of dust fluxes fromanthropogenically disturbed soils:¾ IPCC, 2001: up to 50% (determines radiative forcing)¾ Prospero et al, 2002: small (Natural sources dominant)¾ Luo et al., 2003: 0-50% (‘new desert source’)¾ Yoshioka et al., in press.: <25% (North Africa)¾ Tegen et al., 2004: <10% (Agricultural soils)
Î Large uncertainties!

Regional Soil Studies: WindErosion Prediction
WEQ: Wind Erosion Equation
E = f (I, K, C, L, V)
E: potential soil loss, I: erodibility index,
K: roughness factor, C: climate factor, L: unsheltereddistance across field, V: equivalent vegetative cover.

WEPS: Wind Erosion Prediction System (USDA)
Process based, process sub-models:¾Weather¾Crop Growth¾Decomposition¾Hydrology¾Soil¾Erosion¾Tillage¾ For climate impact studies need particle size information!

Climate Change Impact:
Projected Future Dust Emission Changes
 Changes in meteorology¾Computing dust emission using meteorological fields extracted fromECHAM4 and HADCM3 IPCC future scenarios (IS92a Greenhousewarming).

 Changes in vegetation cover (as consequence of climatechange)¾

Vegetation changes computed with BIOME4 vegetation model.

 Changes in cultivation patterns¾Changes in emissions from cultivated regions computed using resultsfrom the IMAGE2.2 model (RIVM), based on IPCC SRES scenarios.

Regional Dust
Emission Changes:
Projection for 2050
Tegen et al., 2004:
HADCM, ECHAM
Mahowald and Luo, 2003:
NCAR
Global: -60-+20% change inemissions¾ Future estimates in dust
changes vary greatly due touncertainties in climatology andparameterization of dustemissions in global models

Projected Future Dust Emission Changes∆ Natural∆ Natural + Agricultural

Tegen et al., 2004

Changes between 1990 and 2050

For comparison: Mahowald and Luo, 2003: 60% reduced dustemission in 2090

More sources of anthropogenic
soil dust¾ Agricultural tillage: Europe: Probably more
important than wind erosion? (Goossens et al., 2001)¾ Deforestation: ?? Treat as unvegetated areas forwind erosion, possibly small contribution (Tegen andFung, 1995)¾ Offroad traffic: Depending on vehicle speed andweight, PM10 – climate relevance? Small areas(Gillies et al. 2005, Etyemezian, 2004)¾ Construction: Climate relevance? Small areas(Kinsey et al., 2004)

Summary¾ Dust emissions can by impacted by human influence on land
surfaces or as consequence of anthropogenic climatechange.
¾ Global ‘antropogenic’ dust emissions have been estimated to
be up to 50% (IPCC 2001). Recent results indicate thatprobably less than 10-25% of global dust emissions
originate from agricultural soils.
¾ Changes in dust on global scale are likely to be more
controlled by changes in climate and natural vegetation
rather than by changes in cultivated areas.
¾ Regional impacts of anthropogenic soil dust may be large.
¾ Better quantification of anthropogenic dust emission requires
upscaling of wind erosion measurement/ model results, plus
size resolved information (PM2.5).