What feedbacks do fires affect?
- Biogeochemical cycles
- Vegetation composition and structure
- Land-atmosphere water and heat exchanges
- Atmospheric chemistry and composition
- Human health and property
What do fires depend on?
- Vegetation characteristics
- Climate
- Human activities
Give 2 examples of major wildfire events
- 2019-2020 Australian bushfires
- 2015 - Southeast Asian Haze - likely due to strong 2015 El Nino - caused drier-than-usual conditions
Why is it difficult to observe fires?
- Due to high temporal and spatial variability in emissions
- Difficulties involved in conducting measurements in remote forested regions
So observations are predominantly taken using satellites
What are polar satellites - what are strengths/weaknesses?
Most fire estimates are based on polar satellites
Strengths:
- Global coverage
- Frequency of global coverage depends on scan width
- Higher spatial resolution - moderate (1km) - MODIS / High (30m) - Landsat/ASTER
Weaknesses:
- Fewer opportunities for cloud-free observations
- Time resolution - 4 per 24 hours for MODIS Terra/Aqua
- Temporal sampling issues related to diurnal fire cycle
What are the two types of satellites used to observe fires?
- Polar
- Geospatial
What are the strengths and weaknesses of geospatial satellites?
Strengths:
- Hemispheric fire monitoring
- Near real-time data for fire management
- Few/no temporal sampling issues related to diurnal fire cycle
- Broad Direct Broadcast capability
Weaknesses:
- Gaps in global spatial coverage
- Spatial biases in envelope of detectable fires
Where are most fires throughout the year?
- December - Mainly Africa
- April - mostly agricultural fires in southern Russia
- July - southern hemisphere - tropical africa
- September - African fires + south america - Amazon - big fire season
What is the GFED and what does it provide?
Global Fire Emissions Database
- Combine satellite observations with models
- Provide global pictures - estimate emissions
- Emission = Fuel consumption x burned area x emission factor
- Provide info on CO, NOx, VOCs, aerosols etc
- Can provide average carbon emissions from fires - e.g., 2017 - 2.2 PgC/year
- Can also show what types of fires contribute the most
What types of fires dominate contribution to fires?
- Grassland and savannahs are largest contributors : 44%
- Deforestation have substantial contribution
- Peat fires are most variable - coefficient of variation - 176%
What is GFAS, and what does it do?
Global Fire Assimilation System
- Uses fire radiative power (FRP) satellite observations to produce daily estimates of wildfire and biomass burning emissions
- Slight decline overtime - potentially due to land use change - declining savanna fires
- Fires in amazon and Europe increasing
What does fire activity require?
- Biomass resources to burn
- Atmospheric conditions conducive to combustion - dry, hot, windy
- Ignitions - e.g., lightning/human-caused patterns
All 3 affecred by climate in complex ways - over multiple timesclaes
How have fires in Europe been affected by climate?
e.g., 2017 fires in Portugal, France, Italy, Croatia
Caused by:
- Increased temperatures have:
- Extended traditional wildfire season
- Increased the frequency of blazes
How do we try and predict fires in the future and what are the largest sources of uncertainty?
Use models:
- Try and predict how fires will change depending on the change of climate factors in future
- E.g., 16 models ensemble mean change and agreement - Moritz et al., 2012
- But large uncertainty - signal to noise ratio - need signal to be stronger
- Largest source of uncertaintly is precipitation - how this will evolve in future years - temperature also a large uncertainty
What is predicted about fires for the end of the century?
By end of century, likelihood of catastrophic wildfire events will increase by factor of 1.31 to 1.57
- Due to more favourable conditions for fires in future climate
How can humans affect fires? + / -
Start:
- Fire ignition
- Agricultural burning
- Deforestation / land changes
Stop:
- Fire suppression
- Fragmentation of fuel load - through road building, agriculture etc
How can humans use fires for agriculture - e.g., MODIS in indonesia?
- Most fires timed with land cover change - fire used to clear forests
- Little fires in years before land cover change - natural forest has little fire
- Fires after forest loss due to agricultural use
Indicates fires are used to manage regions - to clear land for new agricultural plantations
How can fires affect humans?
- Particulate matter < 2.5 micrometres - PM2.5
- Can cause adverse health affects - respiratory/heart problems
How has wildfire deforestation rate changed in Brazil over time and how has this affected human health - study method?
- Reddington et al., 2015
- Atmospheric model and GFED3 emissions to quantify PM2.5 concs from fires and impact on human health
- 40% reduction in Brazils deforestation rate estimate to prevent ~1060 premature mortalities annually over South America
- Opposite case in Indonesia - more deaths associated with poor air quality
What is the Brazilian Cerrdo and how has it been affected by fires?
- Cerrado is Brazilian tropical savanna - covering ~2 million km^2
- Considered most botanically diverse savanna
- Biodiversity hotspot
- Only 3% of original area is protected
- Historically accounts for more than half of Brazil’s annual burnt area
- 60% of all fires come from savannas
How do fires affect radiation regime?
- Fire emissions include aerosols - very small particles suspended in air
- They affect solar radiation through: Scattering and Absorption
- Observed that they produce reductions in radiation comparable to those resulting from persistent cloud cover
- The net effect on photosynthesis of radiation changes depends on a balance between the reduction in total radiation and increase in its diffuse fraction
- So with diffuse radiation - trees at top receive slightly less radiation, but trees in shade will gain much more GPP - more photosynthesis
- Overall: more diffuse radiation - increases total photosynthesis and GPP
What was found about fires and plant productivity in the Amazon?
- Due to fires = more diffuse radiation = more efficient photosynthesis = higher GPP/NPP
- Effects offset 30-60% of Amazon biomasss burning carbon emissions
- Accounts for 8-16% of the observed Amazon carbon sink
- Rap et al., 2015
