Sandra Isay Saad

Humberto da Rocha

IAG / Department of Atmospheric Sciences

International Scientific ConferenceAmazon in Perspective

Integrated Science for a Sustainable Future

Variation of size and alignment of deforestation patches in Amazonia: trying to understand secondary

circulation and likely effects on rainfall

• Large scale amazonian deforestation

• evapotranspiration decreases

• rainfall decreases

• patchy deforestation:

deforestation breeze ?! (Avissar 2002)

rainfall increases or decreases ?!

currently: cloud increases over

deforestation in dry season

forests in wet season

Simulations of deforestation in meso-scale

Ramos da Silva 2007, 2008Baidya Roy 2002Gandu 2004

Objective

Evaluate impacts of tropical patchy deforestation on local circulation and rainfall, using atmospheric modelling

With dependence of size & alignment relative to large scale wind

• also:

•how large scale flow might combine deforestation breeze, and thus controls rainfall

Othe configuration Atmospheric nudging: NCEP reanalysis

Number of grids: 3

Cumulus parameterization: Grel

Simulations period: 2 months, starting on

•1 October 2002 (dry season)

•1 February 2002 (rainy season)

We used the atmospheric mesoscale model BRAMS BRAMS (Brazilian Regional Atmospheric Modeling System).

Land surface scheme: LEAF

Material & methods

Initial soil moisture profile: horizontally homogeneous (figure), varying with depth and season

Based on field observations Bruno et al. (2006) & Rosolem (2005)

Grids

Extension (km²)Grid spacing

(km)

Grid 1 2.560 x 32.000 64

Grid 2 992 x 992 16

Grid 3 784 x 720 8Grid 1

Topography

• deforestation patches: rectangles ~ 4,000 to 60,000 km²

• aligned N-S (AREA1 to 4), and aligned w/ prevailing wind (AREA1W ... 4W)

EXPERIMENTS Forest Vegetation: Control case = CTL Pasture (Deforestation) case = DFO

Diference (DFO–CTL)

sensible heat flux (H) (Wm-2)

Dry

Sea

son

Rai

ny

seas

on

• Increasing of H specially during dry season.

Diference (DFO–CTL)

latent heat flux (LE) (W m-2)

Dry

Sea

son

Rai

ny

seas

on

• Decreasing of LE only during dry season.

Dry SeasonPrecipitation (DFO – CTL)

Rainy SeasonPrecipitation (DFO – CTL)

Thermodynamics of circulation : Difference (DFO–CTL) q (g/kg) (colour filled); Θ (K) (contour) wind(VH;w×10) (m s-1)

• (A) vortex counter-flow

•Upwd motion downwind the patch

• (C) ascending motion centered over patch

• (D) strongest upward motion

CTL DFO

Horizontal slice 4392

m

vertical profile in 7°S

Impacts on clouds

• processed with grid spacing = 1 km

•hydrometeors:

(cloud + pristine + snow + aggregates + graupel + hail),

(g kg-1)

21:50 UTC

deforestation

• Cloud strenghtening over deforestation

CTL DFO

Aligned N-SAligned with prevailing wind

CONCLUSION

• Simulated pattern of deforestation circulation

• inflow to deforestation accelerates (reduces drag)

•Temperature gradient & cell much stronger in dry season

•increases rainfall extensively along deforestationReduces upwind abruptly Stronger upwd motionTend to Increase net rainfall

•depend on the alignment with the prevailing wind •Cross wind;

•increases rainfall downwind and reduces upwind the deforestation

• tend to decrease net rainfall