Variability Of Biomass Burning Research Articles

Determinants of savanna-fire dynamics in the eastern Lake Victoria catchment (western Kenya) during the last 1200 years

In tropical ecosystems, climate and human impact are generally considered the main determinants of savanna fire distribution, but their relative roles in controlling fire dynamics over the long-term are difficult to assess, due to scarcity of multi-proxy, long-term data. We combined pollen, charcoal and sedimentological data obtained from the 1200-year sediment record of Lake Simbi, a small crater lake near Lake Victoria in western Kenya, to assess the main drivers of century-scale variability in biomass burning, and its long-term effects on local vegetation dynamics. The effect of climate variability was inferred through comparison of the Simbi charcoal time series with an independent reconstruction of the region's moisture-balance history, from the sediment record of nearby Lake Victoria. Our data show that decade-scale climate variability exerted a primary control over burning, with intermediate levels of moisture maximizing the occurrence of fire, in accordance with both spatial and temporal patterns of biomass burning at regional to sub-continental scales. Despite the challenge to identify pre-colonial human impact unambiguously, our data also suggest that human disturbances between 1000 and 1200 AD likely amplified the effect of climate on biomass burning, in contrast to today's situation, where fire prevalence is mostly suppressed due to agricultural landscape fragmentation. Finally, combination of the pollen and charcoal data allowed to quantitatively estimate the effect of fire on vegetation, with fire explaining up to one third of the reconstructed vegetation changes through time. This variability is mostly related to the expansion/contraction of savanna ecosystems, showing that before the 20th century (i.e., the colonial and post-independence periods), fire mediated this region's vegetation changes at century and millennial time scales. Our results produce a long-term historical perspective on the variability of biomass burning in tropical savanna ecosystems, with relevance for assessing future trends resulting from ongoing climate and land-use changes.

Millennial-scale variability in biomass burning covering the interval ~ 41,000–7050 cal BP in the tropical Leizhou Peninsula (south China)

Abstract Here, we present a well-dated terrestrial charcoal chronology covering the interval ~ 41,000–7050 cal BP and identifying the millennial-scale variability in biomass burning for the tropical Leizhou Peninsula, south China. Our results show that changes in biomass burning closely followed regional temperature and precipitation variations on orbital timescales, i.e., more biomass burning occurred during the warm/wet Marine Isotope Stage (MIS) 3, and less biomass burning occurred during the cold/dry MIS 2. Superimposed on this general trend, our charcoal record shows millennial-scale variability in biomass burning corresponding to the rapid climate changes associated with Dansgaard–Oeschger (D–O) cycles, i.e., biomass burning increased during D–O warming events, whereas biomass burning decreased during intervals of rapid cooling terminated by Heinrich events. During the cooler/drier periods, low biomass burning can be explained by the decline of vegetation productivity, whereas the warmer/wetter periods are characterized by higher biomass burning related to increasing fuel availability. Therefore, climate control can be considered as the major forcing factor of biomass burning from 41,000–7050 cal BP on both orbital and millennial timescales in the northern Leizhou Peninsula.

The variability of biomass burning and its influence on regional aerosol properties during the wheat harvest season in North China

The spatial–temporal variation of biomass burning in June during the wheat harvest season in the North China (32–41°N, 111–120°E) and its influence on the regional aerosol optical depth (AOD) and the chemical compositions of size-segregated aerosols in the urban environment were investigated to evaluate the effectiveness of the burn ban policy and the influence on regional pollution. Fire events that occurred in early and middle June accounted for approximately 89% of the events during the month, and fire points located in mid-eastern China (32.5–35.5°N, 114–120°E) comprised 71%. The occurrences exhibit oscillatory changes with a minimum in 2008 (during the Beijing Olympics) and a peak and explosive growth in 2012. Under high relative humidity and south winds, fire emissions from straw burning combined with high urban/industrial emissions to produce intensive regional haze pollution in the North Plain. The formation of secondary inorganic particles was intensified due to the interactions of smoke plumes and urban/industrial pollutants in an urban environment. Higher concentrations and percentages (79%) of sulfate, nitrate, ammonium, and organic carbon in the fine particles under high relative humidity conditions contributed to a deteriorated urban visibility. Therefore, stronger management and a comprehensive ban on wheat straw burning in June are urgently needed, especially during years when the south wind is dominant.

Holocene fire in Fennoscandia and Denmark

Natural disturbance dynamics, such as fire, have a fundamental control on forest composition and structure. Knowledge of fire history and the dominant drivers of fire are becoming increasingly important for conservation and management practice. Temporal and spatial variability in biomass burning is examined here using 170 charcoal and 15 fire scar records collated throughout Fennoscandia and Denmark. The changing fire regime is discussed in relation to local biogeographical controls, regional climatic change, anthropogenic land use and fire suppression. The region has experienced episodic variability in the dominant drivers of biomass burning throughout the Holocene, creating a frequently changing fire regime. Early Holocene biomass burning appears to be driven by fuel availability. Increased continentality during the mid-Holocene Thermal Maximum coincides with an increase in fire. The mid–late Holocene front-like spread of Picea abies (Norway spruce) and cooler, wetter climatic conditions reduce local biomass burning before the onset of intensified anthropogenic land use, and the late Holocene increase in anthropogenic activity created artificially high records of biomass burning that overshadowed the natural fire signal. An economic shift from extensive subsistence land use to agriculture and forestry as well as active fire suppression has reduced regional biomass burning. However, it is proposed that without anthropogenic fire suppression, the underlying natural fire signal would remain low because of the now widespread dominance of P. abies.

Long-term in situ observations of biomass burning aerosol at a high altitude station in Venezuela – sources, impacts and interannual variability

Abstract. First long-term observations of South American biomass burning aerosol within the tropical lower free troposphere are presented. The observations were conducted between 2007 and 2009 at a high altitude station (4765 m a.s.l.) on the Pico Espejo, Venezuela. Sub-micron particle volume, number concentrations of primary particles and particle absorption were observed. Orographic lifting and shallow convection leads to a distinct diurnal cycle at the station. It enables measurements within the lower free troposphere during night-time and observations of boundary layer air masses during daytime and at their transitional regions. The seasonal cycle is defined by a wet rainy season and a dry biomass burning season. The particle load of biomass burning aerosol is dominated by fires in the Venezuelan savannah. Increases of aerosol concentrations could not be linked to long-range transport of biomass burning plumes from the Amazon basin or Africa due to effective wet scavenging of particles. Highest particle concentrations were observed within boundary layer air masses during the dry season. Ambient sub-micron particle volume reached 1.4±1.3 μm3 cm−3, refractory particle number concentrations (at 300 °C) 510±420 cm−3 and the absorption coefficient 0.91±1.2 Mm−1. The respective concentrations were lowest within the lower free troposphere during the wet season and averaged at 0.19±0.25 μm3 cm−3, 150±94 cm−3 and 0.15±0.26 Mm−1. A decrease of particle concentrations during the dry seasons from 2007–2009 could be connected to a decrease in fire activity in the wider region of Venezuela using MODIS satellite observations. The variability of biomass burning is most likely linked to the El Niño–Southern Oscillation (ENSO). Low biomass burning activity in the Venezuelan savannah was observed to follow La Niña conditions, high biomass burning activity followed El Niño conditions.

Predictability of biomass burning in response to climate changes

Climate is an important control on biomass burning, but the sensitivity of fire to changes in temperature and moisture balance has not been quantified. We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo‐ fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote‐sensing observations of month‐by‐month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.

Recent trends in atmospheric methyl bromide: analysis of post-Montreal Protocol variability

Abstract. The atmospheric methyl bromide (CH3Br) burden has declined in recent years, in response to the phaseout of agricultural and structural fumigation consumption under the amendments to the Montreal Protocol. The timing and magnitude of this decrease represents an opportunity to examine our current understanding of atmospheric CH3Br and its budget, response to the phaseout, and response to interannual variability in biomass burning and global OH. In this study, simulations obtained from a time-dependent global model of atmospheric CH3Br emissions and uptake are compared to observations from the NOAA flask network. The model includes a detailed gridded ocean model coupled to a time-dependant atmospheric 2-box model. The phaseout of CH3Br production for agricultural uses began in 1998, concurrent with the pulse in biomass burning associated with the 1998 El Niño. The combined effects of three factors (biomass burning, global OH, and anthropogenic phaseout) appear to explain most of the observed atmospheric methyl bromide variability over the 1997–2008 period. The global budget remains imbalanced, with a large missing source indicated. The missing source does not exhibit a systematic decline during the phaseout period, and therefore, is not the result of significantly underestimating non-QPS agricultural CH3Br emissions. The model results suggest that the oceans should be less undersaturated than before the phaseout began.

Tropospheric ozone and its precursors: reanalysis over the past 45 years and projections for 2030

Within the European Union project RETRO a reconstruction is made of the chemical composition of the troposphere since 1960 with the focus on ozone and its precursors. Long-term simulations are currently being performed using several global chemistry-transport and chemistry-climate models. Meteorological input is provided by the 45-year reanalysis ERA-40, which has recently been completed by the European Centre for Medium-Range Weather Forecasts (ECMWF). Changes in anthropogenic emissions are taken into account by a new inventory covering the whole period; estimates of the interannual variability of biomass burning and biogenic emissions are also included in the models. In this paper we present some preliminary results of this chemical reanalysis, which eventually should include changes in tropospheric ozone and precursor gases as well as in the associated radiative forcing. The results of the reconstruction will also be discussed in the context of future changes to be expected on the basis of the ‘2030 Photcomp’ experiment, which has recently been performed as a contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). In this experiment, projections are made of the air quality and the tropospheric composition for the year 2030 based on the new International Institute for Applied Systems Analysis (IIASA) emission scenarios ‘Current Legislation’ and ‘Maximum Technically Feasible Reduction’ as well as the IPCC Special Report on Emission Scenarios (SRES) scenario A2.

Interannual and seasonal variability of biomass burning emissions constrained by satellite observations

We present a methodology for estimating the seasonal and interannual variation of biomass burning designed for use in global chemical transport models. The average seasonal variation is estimated from 4 years of fire‐count data from the Along Track Scanning Radiometer (ATSR) and 1–2 years of similar data from the Advanced Very High Resolution Radiometer (AVHRR) World Fire Atlases. We use the Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) data product as a surrogate to estimate interannual variability in biomass burning for six regions: Southeast Asia, Indonesia and Malaysia, Brazil, Central America and Mexico, Canada and Alaska, and Asiatic Russia. The AI data set is available from 1979 to the present with an interruption in satellite observations from mid‐1993 to mid‐1996; this data gap is filled where possible with estimates of area burned from the literature for different regions. Between August 1996 and July 2000, the ATSR fire‐counts are used to provide specific locations of emissions and a record of interannual variability throughout the world. We use our methodology to estimate mean seasonal and interannual variations for emissions of carbon monoxide from biomass burning, and we find that no trend is apparent in these emissions over the last two decades, but that there is significant interannual variability.

Biomass dynamics associated with deforestation, fire, and, conversion to cattle pasture in a Mexican tropical dry forest

Few studies have described losses of biomass and structure arising from the conversion of tropical dry forest (TDF) to pasture, a common land-use practice in the most widespread forest type in the Neotropics. We sampled total aboveground biomass (TAGB) at five distinct periods during the process of forest conversion to pasture. TAGB was measured after the primary forests were cut, after the initial forest slash fires, and 1 year after pasture establishment. After 2 years, TAGB was quantified before and after the first pasture fire conducted on site. To capture the variability in biomass burning, two treatments (Baja and Alta) based upon degree of biomass consumed were established in a randomized block design with three treatment blocks. Mean TAGB of the slashed primary forest was 118 Mg ha −1 in the Baja plots and 135 Mg ha −1 in the Alta plots. The slash fires resulted in biomass loss of 62% of the TAGB (75 Mg ha −1) in the Baja treatment and 80% (108 Mg ha −1) in the Alta treatment. The greatest treatment differences in consumption occurred in the large wood (>7.6 cm diameter). Fires in the Baja treatment consumed ∼31% of the large wood, but only 7% in the Alta treatment. Prior to the first pasture fire, TAGB was 40.3 Mg ha −1 in the Baja treatment, and 20.9 Mg ha −1 in the Alta treatment. The pasture fires consumed 63% of the TAGB in the Baja sites and 75% of the TAGB in the Alta treatment. Following the pasture fires, the TAGB was 14.8 Mg ha −1 in the Baja treatment and 7.6 Mg ha −1 in the Alta treatment. In the first 2 years of land cover change from dry forest to pasture there was a dramatic decline in TAGB (and hence aboveground C pools) totaling 87 and 94% of that of pre-disturbance forests. The total biomass lost via fire and decomposition was 113 and 132 Mg ha −1; fire accounted for 89–92% of the loss while decomposition/disappearance comprised 2–11% of the total biomass loss. The widespread distribution of tropical dry forests, their high rates of deforestation, and their high rates of biomass consumption during fires suggest that they are significant anthropogenic sources of atmospheric C. The dramatic loss of biomass and associated high degree of fire severity may also affect future site productivity and the capacity for these sites to function as C pools in the future.