Biomass burning and deforestation as drivers of regional climate change in Amazônia Maria Assunção F Silva Dias IAG/USP & CPTEC/INPE

Amazon Basin Rainfall External forcing –Natural long term variability –Easterlies and westerlies Regional deforestation –Boundary forcing – change in land cover Biomass burning –Boundary forcing – change in land cover –Internal forcing – change in atmospheric composition

OCEAN, LAND SPACE SPACE SOLAR RADIATION SOLAR RADIATION UPWARD INFRARED IINCOMING REFLECTED RADIATION Short Wave Long Wave ATMOSPHERE ATMOSPHERE SCATTERED BY AIR ABSORBED BY H2O, AEROS OZONE 16 RELECTED BY CLOUDS ABSORPTION BY CLOUDS 3 REFLECTED BY SURFACE NET EMISSION BY H2O E CO2 ABSORPTION CLOUD BY H20 & CO2 EMISSION NET SURFACE SENSIBLE LATENT EMISSION HEAT FLUX

SPACE SPACE SOLAR RADIATION SOLAR RADIATION UPWARD INFRARED IINCOMING REFLECTED RADIATION Short Wave Long Wave ATMOSPHERE ATMOSPHERE SCATTERED BY AIR ABSORBED BY H2O, AEROS OZONE 20 RELECTED BY CLOUDS ABSORPTION BY CLOUDS 3 REFLECTED BY SURFACE NET EMISSION BY H2O E CO2 ABSORPTION CLOUD BY H20 & CO2 EMISSION NET SURFACE SENSIBLE LATENT EMISSION HEAT FLUX OCEAN, LAND

Surface forcing

What is the effect of changes in the surface forcing on rainfall?

Durieux, Machado & Laurent, 2003: The effect of deforestation on cloud cover... Deforest (D) Florest (R)

Dry Season More shallow clouds over deforested areas during the afternoon, and less deep convection at night Low Cloud Cover High Cloud Cover

Wet Season Convection stronger at night over deforested areas High Cloud Cover

"More precipitation over deforested areas in the wet season, less in the dry season: increased seasonality - may be a norhtward shift of the equatorial-tropical transition zone" savanization... Durieux et al,

Negri et al, 2004 The Impact of Amazonian Deforestation on Dry Season Rainfall Analysis of 14 years of monthly estimates from the Special Sensor Microwave Imager revealed that only in August did the pattern of rainfall show increases over the deforested region.

Travelling Mesoscale Convective Systems are a main source of precipitation in the Amazon Basin: initial development is a function of surface but MCS “forgets” its origin during the lifetime Satellite IR image Wet Season cm Radar Dry to Wet season 2002

External Forcing

Marengo, 2003 El Niño

Composite annual rainfall departures from the mean for El Niño years for Amazonia

Easterlies and westerlies Intraseasonal oscillations

Jones and Carvalho, 2002 Wet Seasons Easterlies and Westerlies are two modes of the continental scale circulation and are part of the intraseasonal oscillations

W W W W E E E 26 Feb 21 Feb 16 Feb 11 Feb 6 Feb 1 Feb 26 Jan 21 Jan 16 Jan 11 Jan 6 Jan 1999 Low level wind

Blakeslee, 2000 More lightning during the easterlies = deep convective systems with large Ice Water Content Petersen & Rutledge, 2000 Blakeslee,2000 E E E E

Solid line= total rain, dotted line = convective dashed line = stratiform Westerlies Easterlies Rickenbach et al Diurnal cycle more pronounced during easterlies, systems are larger and with larger convective rain fraction

Westerly case “maritime” Easterly case “continental” S-pol Rondônia Petersen, Rutledge 2000 Convective systems are deeper during easterlies

Williams et al, 2002 Easterlies Westerlies Dry to Wet The atmosphere has more aerosol, and more Cloud Condensation Nuclei, during easterlies

Question: what is the role of aerosol in the production of rainfall in the Amazon? Dry to Wet season campaign (September/October 2002) designed to answer this question. Focus on the season when biomass burning increases by a factor of 10 the concentration of Cloud Condensation Nuclei and at the same time there is the onset of the rainy season.

Change in land cover

Aerosol and cloud microphysics interactions

UECE Aircraft in cloud measurements during the DRY to WET season campaign 2002 Reduced cloud droplet size in polluted airmass and a shift of rainfall to upper levels Andreae et al 2004

Aerosol effects Radiation –Colder surface, warmer lower troposphere =stabilizing effect – less clouds → less rainfall? Cloud microphysics –Inhibit rainfall in warm clouds –Deep clouds? Longo et al, 2003 Aerosol Concentration Rainfall accumulation Warm clouds Cold clouds Khain et al, 2003

Monitoring the onset of the rainy season in the Amazon during the DRY to WET transition in 2002 Indicators of the meteorological shift –Change in the upper and low level flow –Change in the intraseasonal oscillations Indicators from the local observations –Widespread deep convection and generalized rainfall –Clean atmosphere

Dynamic/thermodynamic effects Aerosol effects Surface processes (soil moisture, vegetation feedback)

LBA-Dry to Wet Season Campaing Aerosol Concentration September October November

RADAR Vendrasco,, M. Silva Dias, Morales 2004

Daily rainfall (mm)

Daily temperature amplitude Average sensible heat flux Average accumulated rainfall in Rondônia “Onset and End of the Rainy Season in the Brazilian Amazon Basin” – Marengo et al 2001 Onset is defined when rainfall exceeds a given threshold,(2 mm/day during 5 days) provided that average rainfall was well below the threshold before the onset. Ji-Paraná pasture site Dry to Wet transitio 2002 onset

September 2002, 200 hPa December 2002, 200 hPa Upper level shift from westerlies (dry season) to easterlies (rainy season) – Kousky & Kagano, 1981

20 Oct Upper level winds

14 Oct 850 mb LOW LEVEL WINDS

Vitorino & P. Silva Dias 2004 Wavelet analysis of intraseasonal oscillations of low level wind: change in behaviour ~ 10 October

Onset of the rainy season in the Amazon Change in intra seasonal oscillations 10 October Low Level flow14 October Upper level flow20 October ONSET of rainfall~28 October Clean atmosphere1 November

Li & Fu, 2004 Transition of the Large-Scale Atmospheric and Land Surface Conditions from the Dry to the Wet Season over Amazonia as Diagnosed by the ECMWF Re-Analysis LH Lower LH in the observations: may be an indication of the aerosol effect… OBS Rebio Jaru ECMWF

SPACE SPACE SOLAR RADIATION SOLAR RADIATION UPWARD INFRARED IINCOMING REFLECTED RADIATION Short Wave Long Wave ATMOSPHERE ATMOSPHERE SCATTERED BY AIR ABSORBED BY H2O, AEROS OZONE 20 RELECTED BY CLOUDS ABSORPTION BY CLOUDS 3 REFLECTED BY SURFACE NET EMISSION BY H2O E CO2 ABSORPTION CLOUD BY H20 & CO2 EMISSION NET SURFACE SENSIBLE LATENT EMISSION HEAT FLUX OCEAN, LAND

Conclusions Changes in rainfall in the Amazon Basin are very difficult to detect Rainfall is the end product of a very complex system with external and local influences Deforestation has an impact on cloudiness There are indications that regional deforestation may increase rainfall seasonality. Biomass burning aerosol changes the microstructure of clouds. Biomass burning may have an impact on the onset of the rainy season.