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AGW Bushfires of 2019-2020: Bibliography

Posted on: February 4, 2020

Background: The 2019–20 Australian bushfire season began with uncontrolled fires in June 2019. As of January 15 2020, hundreds of fires are burning, mainly in the southeast of the continent with 18.6 million hectares consumed and 6,000 homes and structures destroyed. One billion animals have been killed and some endangered species may be driven to extinction. The cost of these fires is expected to exceed that of the 2009 fires. NASA estimates that 306 million tonnes of CO2 was emitted. The role of ENSO, IOD, and SAM (Southern Annular Mode] in these fires is acknowledged but AGW is claimed as the cause because it is thought that AGW climate change has intensified these climatology cycles and made their impact more severe. It is therefore claimed that the fires are ultimately attributable to fossil fuel emissions of the industrial economy. 

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THIS POST PROVIDES A RELEVANT BIBLIOGRAPHY FOR RESEARCHERS ON THIS TOPIC. SOME VERY RECENT PAPERS ARE MISSING AND WILL BE ADDED ASAP. 

 

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AUSTRALIA: ENSO, IOD, SAM BIBLIOGRAPHY

  1. Ashok, Karumuri, Zhaoyong Guan, and Toshio Yamagata. “Influence of the Indian Ocean Dipole on the Australian winter rainfall.” Geophysical Research Letters 30.15 (2003).  [FULL TEXT]  Using an atmospheric general circulation model and observed datasets of sea surface temperature and rainfall, we studied the influence of the Indian Ocean Dipole (IOD) on the Australian winter rainfall. The IOD has significant negative partial correlations with rainfall over the western and southern regions of Australia. These negative partial correlations extend south‐eastward from Indonesia all the way to south east Australia. Our atmospheric general circulation model sensitivity experiments indicate that cold sea surface temperature anomalies prevailing west of the Indonesian archipelago during the positive IOD events introduce an anomalous anticyclonic circulation at lower levels over the eastern tropical and subtropical Indian Ocean, and over much of the Australian continent. It is also apparent that the response of the atmosphere to the IOD in this region is baroclinic, causing anomalous subsidence and anomalous reduction in the rainfall over the affected regions of Australia.
  2. England, Matthew H., Caroline C. Ummenhofer, and Agus Santoso. “Interannual rainfall extremes over southwest Western Australia linked to Indian Ocean climate variability.” Journal of Climate 19.10 (2006): 1948-1969[FULL TEXT] Interannual rainfall extremes over southwest Western Australia (SWWA) are examined using observations, reanalysis data, and a long-term natural integration of the global coupled climate system. The authors reveal a characteristic dipole pattern of Indian Ocean sea surface temperature (SST) anomalies during extreme rainfall years, remarkably consistent between the reanalysis fields and the coupled climate model but different from most previous definitions of SST dipoles in the region. In particular, the dipole exhibits peak amplitudes in the eastern Indian Ocean adjacent to the west coast of Australia. During dry years, anomalously cool waters appear in the tropical/subtropical eastern Indian Ocean, adjacent to a region of unusually warm water in the subtropics off SWWA. This dipole of anomalous SST seesaws in sign between dry and wet years and appears to occur in phase with a large-scale reorganization of winds over the tropical/subtropical Indian Ocean. The wind field alters SST via anomalous Ekman transport in the tropical Indian Ocean and via anomalous air–sea heat fluxes in the subtropics. The winds also change the large-scale advection of moisture onto the SWWA coast. At the basin scale, the anomalous wind field can be interpreted as an acceleration (deceleration) of the Indian Ocean climatological mean anticyclone during dry (wet) years. In addition, dry (wet) years see a strengthening (weakening) and coinciding southward (northward) shift of the subpolar westerlies, which results in a similar southward (northward) shift of the rain-bearing fronts associated with the subpolar front. A link is also noted between extreme rainfall years and the Indian Ocean Dipole (IOD). Namely, in some years the IOD acts to reinforce the eastern tropical pole of SST described above, and to strengthen wind anomalies along the northern flank of the Indian Ocean anticyclone. In this manner, both tropical and extratropical processes in the Indian Ocean generate SST and wind anomalies off SWWA, which lead to moisture transport and rainfall extremes in the region. An analysis of the seasonal evolution of the climate extremes reveals a progressive amplification of anomalies in SST and atmospheric circulation toward a wintertime maximum, coinciding with the season of highest SWWA rainfall. The anomalies in SST can appear as early as the summertime months, however, which may have important implications for predictability of SWWA rainfall extremes.
  3. Gillett, N. Pꎬ, T. Dꎬ Kell, and P. D. Jones. “Regional climate impacts of the Southern Annular Mode.” Geophysical Research Letters 33.23 (2006)[FULL TEXT]  Previous work on the influence of the Southern Annular Mode (SAM) on surface climate has focused mainly on individual countries. In this study we use station observations of temperature and rainfall to identify the influence of the SAM on land regions over the whole of the Southern Hemisphere. We demonstrate that the positive phase of the SAM is associated with a significant cooling over Antarctica and much of Australia, and a significant warming over the Antarctic Peninsula, Argentina, Tasmania and the south of New Zealand. The positive phase of the SAM is also associated with anomalously dry conditions over southern South America, New Zealand and Tasmania, due to the southward shift of the stormtrack; and to anomalously wet conditions over much of Australia and South Africa. These influences on populated regions of the Southern Hemisphere may have implications for weather and seasonal forecasting, and for future climate change.
  4. A review of recent climate variability and climate change in southeastern Australia, Bradley F. Murphy Bertrand Timbal, First published:15 October 2007 https://doi.org/10.1002/joc.1627 Southeastern Australia (SEA) has suffered from 10 years of low rainfall from 1997 to 2006. A protracted dry spell of this severity has been recorded once before during the 20th century, but current drought conditions are exacerbated by increasing temperatures. Impacts of this dry decade are wide‐ranging, so a major research effort is being directed to better understand the region’s recent climate, its variability and climate change. This review summarizes the conditions of these 10 years and the main mechanisms that affect the climate.Most of the rainfall decline (61%) has occurred in autumn (March–May). Daily maximum temperatures are rising, as are minimum temperatures, except for cooler nights in autumn in the southwest of SEA closely related to lower rainfall. A similar rainfall decline occurred in the southwest of western Australia around 1970 that has many common features with the SEA decline. SEA rainfall is produced by mid‐latitude storms and fronts, interactions with the tropics through continental‐scale cloudbands and cut‐off lows. El Niño‐Southern Oscillation impacts on SEA rainfall, as does the Indian Ocean, but neither has a direct influence in autumn. Trends have been found in both hemispheric (the southern annular mode) and local (sub‐tropical ridge) circulation features that may have played a role in reducing the number and impact of mid‐latitude systems around SEA, and thus reducing rainfall. The role of many of these mechanisms needs to be clarified, but there is likely to be an influence of enhanced greenhouse gas concentrations on SEA climate, at least on temperature. Copyright © 2007 Royal Meteorological Society
  5. Abram, Nerilie J., et al. “Seasonal characteristics of the Indian Ocean Dipole during the Holocene epoch.” Nature 445.7125 (2007): 299-302. The Indian Ocean Dipole1,2 (IOD)—an oscillatory mode of coupled ocean–atmosphere variability—causes climatic extremes and socio-economic hardship throughout the tropical Indian Ocean region1,2,3,4,5. There is much debate about how the IOD interacts with the El Niño/Southern Oscillation (ENSO) and the Asian monsoon, and recent changes in the historic ENSO–monsoon relationship6 raise the possibility that the properties of the IOD may also be evolving. Improving our understanding of IOD events and their climatic impacts thus requires the development of records defining IOD activity in different climatic settings, including prehistoric times when ENSO and the Asian monsoon behaved differently from the present day. Here we use coral geochemical records from the equatorial eastern Indian Ocean to reconstruct surface-ocean cooling and drought during individual IOD events over the past 6,500 years. We find that IOD events during the middle Holocene were characterized by a longer duration of strong surface ocean cooling, together with droughts that peaked later than those expected by El Niño forcing alone. Climate model simulations suggest that this enhanced cooling and drying was the result of strong cross-equatorial winds driven by the strengthened Asian monsoon of the middle Holocene. These IOD–monsoon connections imply that the socioeconomic impacts of projected future changes in Asian monsoon strength may extend throughout Australasia.
  6. Cai, W., T. Cowan, and M. Raupach. “Positive Indian Ocean dipole events precondition southeast Australia bushfires.” Geophysical Research Letters 36.19 (2009). [FULL TEXT] The devastating “Black Saturday” bushfire inferno in the southeast Australian state of Victoria in early February 2009 and the “Ash Wednesday” bushfires in February 1983 were both preceded by a positive Indian Ocean Dipole (pIOD) event. Is there a systematic pIOD linkage beyond these two natural disasters? We show that out of 21 significant bushfires seasons since 1950, 11 were preceded by a pIOD. During Victoria’s wet season, particularly spring, a pIOD contributes to lower rainfall and higher temperatures exacerbating the dry conditions and increasing the fuel load leading into summer. Consequently, pIODs are effective in preconditioning Victoria for bushfires, more so than El Niño events, as seen in the impact on soil moisture on interannual time scales and in multi‐decadal changes since the 1950s. Given that the recent increase in pIOD occurrences is consistent with what is expected from global warming, an increased bushfire risk in the future is likely across southeast Australia.
  7. Cai, W., T. Cowan, and A. Sullivan. “Recent unprecedented skewness towards positive Indian Ocean Dipole occurrences and its impact on Australian rainfall.” Geophysical Research Letters 36.11 (2009)[FULL TEXT]  Is the recent high frequency of positive Indian Ocean Dipole (pIOD) events a consequence of global warming? Using available observations and reanalyses, we show that the pIOD occurrences increase from about four per 30 years early in the 20th century to about 10 over the last 30 years; by contrast, the number of negative Indian Ocean Dipole (nIOD) events decreases from about 10 to two over the same periods, respectively. A skewness measure, defined as the difference in occurrences of pIODs and nIODs, illustrates a systematic trend in this parameter commencing early in the 20th century. After 1950, there are more pIODs than nIODs, with consistent mean circulation changes in the pIOD‐prevalent seasons. Over southeastern Australia (SEA), these changes potentially account for much of the observed austral winter and spring rainfall reduction since 1950. These features are consistent with projected future climate change and hence with what is expected from global warming.
  8. Taschetto, Andrea S., et al. “The contribution of Indian Ocean sea surface temperature anomalies on Australian summer rainfall during El Niño events.” Journal of Climate 24.14 (2011): 3734-3747. [FULL TEXT] This study investigates the impact of Indian Ocean sea surface temperature (SST) anomalies on the atmospheric circulation of the Southern Hemisphere during El Niño events, with a focus on Australian climate. During El Niño episodes, the tropical Indian Ocean exhibits two types of SST response: a uniform “basinwide warming” and a dipole mode—the Indian Ocean dipole (IOD). While the impacts of the IOD on climate have been extensively studied, the effects of the basinwide warming, particularly in the Southern Hemisphere, have received less attention. The interannual basinwide warming response has important implications for Southern Hemisphere atmospheric circulation because 1) it accounts for a greater portion of the Indian Ocean monthly SST variance than the IOD pattern and 2) its maximum amplitude occurs during austral summer to early autumn, when large parts of Australia, South America, and Africa experience their monsoon. Using observations and numerical experiments with an atmospheric general circulation model forced with historical SST from 1949 to 2005 over different tropical domains, the authors show that the basinwide warming leads to a Gill–Matsuno-type response that reinforces the anomalies caused by changes in the Pacific as part of El Niño. In particular, the basinwide warming drives strong subsidence over Australia, prolonging the dry conditions during January–March, when El Niño–related SST starts to decay. In addition to the anomalous circulation in the tropics, the basinwide warming excites a pair of barotropic anomalies in the Indian Ocean extratropics that induces an anomalous anticyclone in the Great Australian Bight.
  9. Werner, Angelika, Angela M. Maharaj, and Neil J. Holbrook. “A new method for extracting the ENSO-independent Indian Ocean Dipole: application to Australian region tropical cyclone counts.” Climate dynamics 38.11-12 (2012): 2503-2511.  We introduce a simple but effective means of removing ENSO-related variations from the Indian Ocean Dipole (IOD) in order to better evaluate the ENSO-independent IOD contribution to Australian climate—specifically here interannual variations in Australian region tropical cyclogensis (TCG) counts. The ENSO time contribution is removed from the Indian Ocean Dipole Mode index (DMI) by first calculating the lagged regression of the DMI on the sea surface temperature anomaly (SSTA) index NINO3.4 to maximum lags of 8 months, and then removing this ENSO portion. The new ENSO-independent time series, DMINOENSO, correlates strongly with the original DMI at r = 0.87 (significant at >99% level). Despite the strength of the correlation between these series, the IOD events classified based on DMINOENSO provide important differences from previously identified IOD events, which are more closely aligned with ENSO phases. IOD event composite maps of SSTAs regressed on DMINOENSO reveal a much greater ENSO-independence than the original DMI-related SSTA pattern. This approach is used to explore relationships between Australian region TCG and IOD from 1968 to 2007. While we show that both the DMI and DMINOENSO have significant hindcast skill (on the 95% level) when used as predictors in a multiple linear regression model for Australian region annual TCG counts, the IOD does not add any significant hindcast skill over an ENSO-only predictor model, based on NINO4. Correlations between the time series of annual TCG count observations and ENSO + IOD model cross-validated hindcasts achieve r = 0.68 (significant at the 99% level).
  10. Pui, Alexander, et al. “Impact of the El Niño–Southern Oscillation, Indian Ocean dipole, and southern annular mode on daily to subdaily rainfall characteristics in east Australia.” Monthly weather review 140.5 (2012): 1665-1682 [FULL TEXT] The relationship between seasonal aggregate rainfall and large-scale climate modes, particularly the El Niño–Southern Oscillation (ENSO), has been the subject of a significant and ongoing research effort. However, relatively little is known about how the character of individual rainfall events varies as a function of each of these climate modes. This study investigates the change in rainfall occurrence, intensity, and storm interevent time at both daily and subdaily time scales in east Australia, as a function of indices for ENSO, the Indian Ocean dipole (IOD), and the southern annular mode (SAM), with a focus on the cool season months. Long-record datasets have been used to sample a large variety of climate events for better statistical significance. Results using both the daily and subdaily rainfall datasets consistently show that it is the occurrence of rainfall events, rather than the average intensity of rainfall during the events, which is most strongly influenced by each of the climate modes. This is shown to be most likely associated with changes to the time between wet spells. Furthermore, it is found that despite the recent attention in the research literature on other climate modes, ENSO remains the leading driver of rainfall variability over east Australia, particularly farther inland during the winter and spring seasons. These results have important implications for how water resources are managed, as well as how the implications of large-scale climate modes are included in rainfall models to best capture interannual and longer-scale variability.
  11. Cai, Wenju, et al. “Projected response of the Indian Ocean Dipole to greenhouse warming.” Nature geoscience 6.12 (2013): 999-1007.  Natural modes of variability centred in the tropics, such as the El Niño/Southern Oscillation and the Indian Ocean Dipole, are a significant source of interannual climate variability across the globe. Future climate warming could alter these modes of variability. For example, with the warming projected for the end of the twenty-first century, the mean climate of the tropical Indian Ocean is expected to change considerably. These changes have the potential to affect the Indian Ocean Dipole, currently characterized by an alternation of anomalous cooling in the eastern tropical Indian Ocean and warming in the west in a positive dipole event, and the reverse pattern for negative events. The amplitude of positive events is generally greater than that of negative events. Mean climate warming in austral spring is expected to lead to stronger easterly winds just south of the Equator, faster warming of sea surface temperatures in the western Indian Ocean compared with the eastern basin, and a shoaling equatorial thermocline. The mean climate conditions that result from these changes more closely resemble a positive dipole state. However, defined relative to the mean state at any given time, the overall frequency of events is not projected to change — but we expect a reduction in the difference in amplitude between positive and negative dipole events.
  12. Abram, Nerilie J., et al. “Evolution of the Southern Annular Mode during the past millennium.” Nature Climate Change 4.7 (2014): 564-569.  The Southern Annular Mode (SAM) is the primary pattern of climate variability in the Southern Hemisphere1,2, influencing latitudinal rainfall distribution and temperatures from the subtropics to Antarctica. The positive summer trend in the SAM over recent decades is widely attributed to stratospheric ozone depletion2; however, the brevity of observational records from Antarctica1—one of the core zones that defines SAM variability—limits our understanding of long-term SAM behaviour. Reconstructed SAM trends before the twentieth century are more prominent than those in radiative-forcing climate experiments and may be associated with a teleconnected response to tropical Pacific climate. Our findings imply that predictions of further greenhouse-driven increases in the SAM over the coming century3 also need to account for the possibility of opposing effects from tropical Pacific climate changes.
  13. Pepler, A., et al. “Indian Ocean Dipole overrides ENSO’s influence on cool season rainfall across the Eastern Seaboard of Australia.” Journal of Climate 27.10 (2014): 3816-3826. [FULL TEXT]  The strong relationship between Eastern Australian winter–spring rainfall and tropical modes of variability such as the El Niño–Southern Oscillation (ENSO) does not extend to the heavily populated coastal strip east of the Great Dividing Range in southeast Australia, where correlations between rainfall and Niño-3.4 are insignificant during June–October. The Indian Ocean dipole (IOD) is found to have a strong influence on zonal wind flow during the winter and spring months, with positive IOD increasing both onshore winds and rainfall over the coastal strip, while decreasing rainfall elsewhere in southeast Australia. The IOD thus opposes the influence of ENSO over the coastal strip, and this is shown to be the primary cause of the breakdown of the ENSO–rainfall relationship in this region.
  14. Sharples, Jason J., et al. “Natural hazards in Australia: extreme bushfire.” Climatic Change 139.1 (2016): 85-99.  Bushfires are one of the most frequent natural hazards experienced in Australia. Fires play an important role in shaping the landscape and its ecological dynamics, but may also have devastating effects that cause human injuries and fatalities, as well as broad-scale environmental damage. While there has been considerable effort to quantify changes in the occurrence of bushfire in Australia, a comprehensive assessment of the most extreme bushfire cases, which exact the greatest economic and environmental impacts, is lacking. In this paper we reflect upon recently developed understanding of bushfire dynamics to consider (i) historical changes in the occurrence of extreme bushfires, and (ii) the potential for increasing frequency in the future under climate change projections. The science of extreme bushfires is still a developing area, thus our conclusions about emerging patterns in their occurrence should be considered tentative. Nonetheless, historical information on noteworthy bushfire events suggests an increased occurrence in recent decades. Based on our best current understanding of how extreme bushfires develop, there is strong potential for them to increase in frequency in the future. As such there is a pressing need for a greater understanding of these powerful and often destructive phenomena.
  15. Mariani, Michela, and Michael‐Shawn Fletcher. “The Southern Annular Mode determines interannual and centennial‐scale fire activity in temperate southwest Tasmania, Australia.” Geophysical Research Letters 43.4 (2016): 1702-1709.  [FULL TEXT] Southern Annular Mode (SAM) is the primary mode of atmospheric variability in the Southern Hemisphere. While it is well established that the current anthropogenic‐driven trend in SAM is responsible for decreased rainfall in southern Australia, its role in driving fire regimes in this region has not been explored. We examined the connection between fire activity and SAM in southwest Tasmania, which lies in the latitudinal band of strongest correlation between SAM and rainfall in the Southern Hemisphere. We reveal that fire activity during a fire season is significantly correlated with the phase of SAM in the preceding year using superposed epoch analysis. We then synthesized new 14 charcoal records from southwest Tasmania spanning the last 1000 years, revealing a tight coupling between fire activity and SAM at centennial timescales, observing a multicentury increase in fire activity over the last 500 years and a spike in fire activity in the 21st century in response to natural and anthropogenic SAM trends.
  16. Dowdy, Andrew J., Michael D. Fromm, and Nicholas McCarthy. “Pyrocumulonimbus lightning and fire ignition on Black Saturday in southeast Australia.” Journal of Geophysical Research: Atmospheres 122.14 (2017): 7342-7354A number of devastating wildfires occurred in southeast Australia on 7 February 2009, colloquially known as Black Saturday. Atmospheric responses to this extreme fire event are investigated here with a focus on convective processes associated with fire activity (i.e., pyroconvection). We examine six different fire complexes on Black Saturday, finding three clearly distinct pyrocumulonimbus storms, the largest of which reached heights of 15 km on that day and generated hundreds of lightning strokes. The first lightning stroke was recorded near the largest fire complex 5 h after fire ignition. One of the pyrocumulonimbus storms was initiated close to midnight due to mesoscale influences, consistent with extreme fire behavior observed at that time for that particular fire. As another example of fire‐atmosphere interactions, a fire that started late on Black Saturday is examined in relation to ignition caused by pyrogenic lightning, with implications for understanding the maximum rate of spread of a wildfire. Results are discussed in relation to another pyrocumulonimbus event associated with the 2003 Canberra fires. Our findings are intended to provide a greater understanding of pyroconvection and fire‐atmosphere feedback processes, as well as help enhance wildfire response capabilities. We also demonstrate the potential for using lightning, radar, and satellite remote sensing in combination with thermodynamic analyses as well as synoptic and mesoscale dynamics to provide enhanced real‐time guidance for dangerous fire conditions associated with pyroconvection, as well as for the risk of new fire ignitions from pyrogenic lightning.

 

 

 

AUSTRALIA PALEOCLIMATE BIBLIOGRAPHY

  1. Heusser, Linda E., and Guus Van de Geer. “Direct correlation of terrestrial and marine paleoclimatic records from four glacial-interglacial cycles—DSDP Site 594 Southwest Pacific.” Quaternary Science Reviews 13.3 (1994): 273-282.  Over the last ∼350 ka, changes in the composition of vegetation on New Zealand (inferred from pollen analysis of the upper 40 m of DSDP Site 594 at ∼2.4 ka sample intervals) reflect regional climatic variations which appear synchronous with implied variations in glacier fluctuation and in global climatostratigraphy described from sedimentary and oxygen isotope records from the same samples (Nelson et al., 1985). Pollen assemblages from Isotope Stages 1, 5e, 7a, 7b and 9 are distinguished by conifer and broadleaf forest taxa which vary in composition between the last four interglacials, suggesting significant differences in precipitation, temperature, and/or migration rates. Glacial pollen assemblages, which imply the expansion of herbland and decline in forest components, show less variation and generally indicate comparatively cool conditions on the east coast of South Island. Interstadial vegetation is composed of a mosaic of shrubland/herbland vegetation. The close correspondence between variations in the amplitude and timing of these continuous records of forest development in the changing vegetation of South Island, New Zealand, and oxygen isotope climatostratigraphy supports previous suggestions that Late Quaternary southern and northern hemisphere climatic fluctuations were essentially synchronous.
  2. Joussaume, S., and K. E. Taylor. “Status of the paleoclimate modeling intercomparison project (PMIP).” World Meteorological Organization-Publications-WMO TD (1995): 425-430[FULL TEXT] Partly inspired by AMIP, the Paleoclimate Modeling Intercomparison Project (PMIP) was initiated in order to coordinate and encourage the systematic study of atmospheric general circulation models (AGCMs) and to assess their ability to simulate large changes of climate such as those that occurred in the distant past. Project goals include identifying common responses of AGCMs to imposed paleoclimate “boundary conditions,” understanding the differences in model responses, comparing model results with paleoclimate data, and providing AGCM results for use in helping in the analysis and interpretation of paleoclimate data. PMIP is initially focussing on the mid-Holocene (6,000 years Before Present) and the last glacial maximum (21,000 yr BP) because climatic conditions were remarkably different at those times and because relatively large amounts of paleoclimate data exist for these periods. The major “forcing” factors are also relatively well known at these times. Some of the paleoclimate features simulated by models in previous studies seem consistent with paleoclimatic data, but others do not. One of the goals of PMIP is to determine which results are model-dependent. The PMIP experiments are limited to studying the equilibrium response of the atmosphere (and such surface characteristics as snow cover) to changes in boundary conditions (e.g., insolation, ice-sheet distribution, CO2 concentration, etc.) PMIP has been endorsed by both IGBP/PAGES and WCRP/WGNE, and more than fifteen modeling groups are participating. Several of these groups have completed one or more of the PMIP simulations. Model output will be archived at the Program for Climate Model Diagnosis and Intercomparison (PCMDI) in a structure similar to the AMIP standard output. A workshop involving a representative of each of the PMIP modeling groups is planned for the Fall of 1995 in which results from the PMIP simulations will be shared and subprojects focussing on specific issues will be formed.
  3. Baldini, J. U. L., F. McDermott, and I. J. Fairchild. “Spatial variability in cave drip water hydrochemistry: Implications for stalagmite paleoclimate records.” Chemical Geology 235.3-4 (2006): 390-404.  The identification of vadose zone hydrological pathways that most accurately transmit climate signals through karst aquifers to stalagmites is critical for accurately interpreting climate proxies contained within individual stalagmites. A three-year cave drip hydrochemical study across a spectrum of drip types in Crag Cave, SW Ireland, reveals substantial variability in drip hydrochemical behaviour. Stalagmites fed by very slow drips (< 0.1 ml/min) may best retain information regarding decadal- through millennial-scale climate because the drip sites’ diffuse recharge minimizes interferences to the long-term pattern produced by isolated meteorological events. Additionally, hydrological routing shifts did not influence these very slow drips. Intermediate flow regimes (0.1–2 ml/min) are apparently most sensitive to water excess, and may best preserve a paleoseasonality signal because of a combination of rapid stalagmite growth, seasonally responsive drip rates, and minimal interferences from stochastic processes within the aquifer. Stochastic drip-rate variability existed at several high-discharge (> 2 ml/min) sites, apparently unconnected with local meteorological events. Water from these drips was typically undersaturated with respect to calcite, and thus did not result in calcite deposition. Data presented here suggest that drips in this flow regime also experience flow re-routing and blocking, and that any stalagmites developed under such drips are unsuitable as mid- to high-resolution paleoclimate proxies. Most drip sites demonstrated seasonal [Ca2+] and [Mg2+] variability that was probably linked to water excess. Prior calcite precipitation along the flowpath affected the chemistry of slowly dripping sites, while dilution predominantly controlled the water chemistry of the more rapidly dripping sites. This research underscores the importance of understanding drip hydrology prior to selecting stalagmites for paleoclimate analysis and before interpreting any subsequent proxy data.
  4. Verdon, Danielle C., and Stewart W. Franks. “Long‐term behaviour of ENSO: Interactions with the PDO over the past 400 years inferred from paleoclimate records.” Geophysical Research Letters 33.6 (2006).  This study uses proxy climate records derived from paleoclimate data to investigate the long‐term behaviour of the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO). During the past 400 years, climate shifts associated with changes in the PDO are shown to have occurred with a similar frequency to those documented in the 20th Century. Importantly, phase changes in the PDO have a propensity to coincide with changes in the relative frequency of ENSO events, where the positive phase of the PDO is associated with an enhanced frequency of El Niño events, while the negative phase is shown to be more favourable for the development of La Niña events.
  5. Verdon**, D., and S. W. Franks. “Long-term drought risk assessment in the Lachlan River Valley–A paleoclimate perspective.” Australasian Journal of Water Resources 11.2 (2007): 145-152.  The frequency and severity of droughts during the past two decades in eastern Australia have caused water resource managers to question the suitability of current drought management practices. For example, water accounting schemes in NSW (and elsewhere) use an estimate of the “worst drought in 100 years” for resource assessment, which is based solely on the instrumental record. However, inflows during the most recent drought (2002–2007) were lower than those recorded in the last 100 years for some of the catchments in NSW. This resulted in an overestimate of expected inflows and critically low storage volumes (ie. failure of the system). It is clear that hydrological drought risk would be better assessed by extending the records beyond the single 100 year instrumental record, so as to capture a larger spectrum of climatic variability. Incorporating paleoclimate information on the major climate drivers for the region may provide the critical insight required to achieve this goal. In this paper, proxy climate records derived from paleoclimate data are used to investigate the long-term behaviour of the Interdecadal Pacific Oscillation (IPO) and the El Niño/Southern Oscillation (ENSO). This information is then used to develop a stochastic framework for generating rainfall replicates to be used in assessing long-term hydrologic drought risk for water resource management in NSW. Importantly, the rainfall replicates demonstrate that this region may have experienced meteorological droughts of longer duration than has been recorded by the instrumental record. This result highlights the possibility that current management practices may fail to meet needs in the future, if history were to be repeated.
  6. Woodhead, Jon, et al. “Speleothem climate records from deep time? Exploring the potential with an example from the Permian.” Geology 38.5 (2010): 455-458.  Speleothems are well-proven archives of terrestrial climate variation, recording mean temperature, rainfall, and surface vegetation data at subannual to millennial resolution. They also form within the generally stable environment of caves, and thus may remain remarkably well preserved for many millions of years and, most important, can be dated radiometrically to provide robust chronologies that do not rely on orbital tuning, ice-flow modeling, or estimates of sediment deposition rates. The recent adaptation of the U-Pb dating technique to speleothems has greatly extended their potential as paleoclimate recorders back into the more distant geological past, well beyond the ∼500 k.y. limit previously imposed by U-series techniques, but the opportunities presented by these new methods have yet to be fully explored. As an extreme example, here we report on samples recovered from Permian cave fills, the oldest radiometrically dated speleothems so far documented. Using state of the art analytical techniques it is possible to determine not only their age and state of preservation, but also to extract apparently nearly pristine climate proxy data. Armed with these methods, it now seems reasonable to apply the lessons learned from more recent speleothems to ancient materials, wherever they can be found, and of whatever age, to generate snapshots of paleoclimate that can be used to greatly refine the records preserved within the sediments and fossils of the time.
  7. Lough, Janice M. “Climate records from corals.” Wiley interdisciplinary reviews: climate change 1.3 (2010): 318-331.  Understanding the nature and causes of climate variability and change in the tropical oceans—the heat engine of the global climate system—is limited by the relatively short length of instrumental records. Certain massive reef‐building corals contain a wealth of historical proxy climate and environmental information locked in their calcium carbonate skeletons. This information is available from living corals that can be up to several hundred years old and from fossil corals, often well preserved after death, for well‐dated windows of the more distant past. Continuous, high‐resolution (annual to seasonal) information from such corals is provided by a range of measures that include growth characteristics which can document coral responses to unusual environmental conditions and various geochemical tracers whose incorporation into the skeleton is mediated by ambient seawater characteristics. The stable oxygen isotope ratio, δ18O, has been the most commonly measured coral environmental tracer and, although reflecting both sea surface temperature and seawater salinity, long records of this variable are providing new insights into interannual (e.g., El Niño‐Southern Oscillation), decadal, and longer time‐scale variability in the tropical oceans—information not accessible from the instrumental records—which complements other sources of high‐resolution proxy climate information (e.g., tree rings, ice cores, documentary records). The contribution of proxy climate records in corals to the global picture of past climates is being enhanced through efforts to reduce the various sources of uncertainty that can confound the interpretation of any source of proxy climate information. Copyright © 2010 John Wiley & Sons, Ltd.
  8. Phipps, Steven J., et al. “Paleoclimate data–model comparison and the role of climate forcings over the past 1500 years.” Journal of Climate 26.18 (2013): 6915-6936[FULL TEXT] The past 1500 years provide a valuable opportunity to study the response of the climate system to external forcings. However, the integration of paleoclimate proxies with climate modeling is critical to improving the understanding of climate dynamics. In this paper, a climate system model and proxy records are therefore used to study the role of natural and anthropogenic forcings in driving the global climate. The inverse and forward approaches to paleoclimate data–model comparison are applied, and sources of uncertainty are identified and discussed. In the first of two case studies, the climate model simulations are compared with multiproxy temperature reconstructions. Robust solar and volcanic signals are detected in Southern Hemisphere temperatures, with a possible volcanic signal detected in the Northern Hemisphere. The anthropogenic signal dominates during the industrial period. It is also found that seasonal and geographical biases may cause multiproxy reconstructions to overestimate the magnitude of the long-term preindustrial cooling trend. In the second case study, the model simulations are compared with a coral δ18O record from the central Pacific Ocean. It is found that greenhouse gases, solar irradiance, and volcanic eruptions all influence the mean state of the central Pacific, but there is no evidence that natural or anthropogenic forcings have any systematic impact on El Niño–Southern Oscillation. The proxy climate relationship is found to change over time, challenging the assumption of stationarity that underlies the interpretation of paleoclimate proxies. These case studies demonstrate the value of paleoclimate data–model comparison but also highlight the limitations of current techniques and demonstrate the need to develop alternative approaches.
  9. Ho, Michelle, Anthony S. Kiem, and Danielle C. Verdon‐Kidd. “A paleoclimate rainfall reconstruction in the Murray‐Darling Basin (MDB), Australia: 2. Assessing hydroclimatic risk using paleoclimate records of wet and dry epochs.” Water Resources Research 51.10 (2015): 8380-8396.  [FULL TEXT] .  Estimates of hydrological risk are crucial to enable adequate planning and preparation for extreme events. However, the accurate estimation of hydrological risk is hampered by relatively short instrumental records in many parts of the world. Information derived from climate‐sensitive paleoclimate proxies provide an opportunity to resolve hydroclimatic variability, but many regions, such as Australia’s Murray‐Darling Basin (MDB), currently lack the suitable in situ proxies necessary to do this. Here new MDB rainfall reconstructions are presented based on a novel method using paleoclimate rainfall proxies in the Australasian region spanning from 749 B.C.E. to 1980 C.E. Our results emphasize the need to develop additional reconstructions and, with the companion paper, demonstrate how this information can be used to benefit water resource management. This study shows that prior to the twentieth century, both dry and wet epochs have persisted for longer periods than observed in the instrumental record—with the probability of both dry and wet periods exceeding a decade at least 10 times more likely prior to 1883 than suggested by the instrumental records. Some reconstructed rainfalls exceeded the instrumental range (i.e., drier dry epochs and wetter wet spells) despite a systematic underestimation of extremes due to a combination of proxy quality and model bias. Importantly, the results demonstrate that the instrumental record does not cover the full range of hydroclimatic variability possible in the MDB. Therefore, hydroclimatic risk assessments based on the instrumental record likely underestimate, or at least misinterpret, the frequency, duration, and magnitude of wet and dry epochs.

 

 

AGW AND WILDFIRES BIBLIOGRAPHY

  1. Goldammer, Johann Georg, and Colin Price. “Potential impacts of climate change on fire regimes in the tropics based on MAGICC and a GISS GCM-derived lightning model.” Climatic Change 39.2-3 (1998): 273-296.  Investigations of the ecological, atmospheric chemical, and climatic impacts of contemporary fires in tropical vegetation have received increasing attention during the last 10 years. Little is known, however, about the impacts of climate changes on tropical vegetation and wildland fires. This paper summarizes the main known interactions of fire, vegetation, and atmosphere. Examples of predictive models on the impacts of climate change on the boreal and temperate zones are given in order to highlight the possible impacts on the tropical forest and savanna biomes and to demonstrate parameters that need to be involved in this process. Response of tropical vegetation to fire is characterized by degradation towards xerophytic and pyrophytic plant communities dominated by grasses and fire-tolerant tree and bush invaders. The potential impacts of climate change on tropical fire regimes are investigated using a GISS GCM-based lightning and fire model and the Model for the Assessment of Greenhouse Gas-Induced Climate Change (MAGICC).
  2. Bond, W. J., G. F. Midgley, and F. I. Woodward. “The importance of low atmospheric CO2 and fire in promoting the spread of grasslands and savannas.” Global Change Biology 9.7 (2003): 973-982.  The distribution and abundance of trees can be strongly affected by disturbance such as fire. In mixed tree/grass ecosystems, recurrent grass‐fuelled fires can strongly suppress tree saplings and therefore control tree dominance. We propose that changes in atmospheric [CO2] could influence tree cover in such metastable ecosystems by altering their postburn recovery rates relative to flammable herbaceous growth forms such as grasses. Slow sapling recovery rates at low [CO2] would favour the spread of grasses and a reduction of tree cover. To test the possible importance of [CO2]/fire interactions, we first used a Dynamic Global Vegetation Model (DGVM) to simulate biomass in grassy ecosystems in South Africa with and without fire. The results indicate that fire has a major effect under higher rainfall conditions suggesting an important role for fire/[CO2] interactions. We then used a demographic model of the effects of fire on mesic savanna trees to test the importance of grass/tree differences in postburn recovery rates. We adjusted grass and tree growth in the model according to the DGVM output of net primary production at different [CO2] relative to current conditions. The simulations predicted elimination of trees at [CO2] typical of the last glacial period (180 ppm) because tree growth rate is too slow (15 years) to grow to a fire‐proof size of ca. 3 m. Simulated grass growth would produce an adequate fuel load for a burn in only 2 years. Simulations of preindustrial [CO2] (270 ppm) predict occurrence of trees but at low densities. The greatest increase in trees occurs from preindustrial to current [CO2] (360 ppm). The simulations are consistent with palaeo‐records which indicate that trees disappeared from sites that are currently savannas in South Africa in the last glacial. Savanna trees reappeared in the Holocene. There has also been a large increase in trees over the last 50–100 years. We suggest that slow tree recovery after fire, rather than differential photosynthetic efficiencies in C3 and C4 plants, might have been the significant factor in the Late Tertiary spread of flammable grasslands under low [CO2] because open, high light environments would have been a prerequisite for the spread of C4 grasses. Our simulations suggest further that low [CO2] could have been a significant factor in the reduction of trees during glacial times, because of their slower regrowth after disturbance, with fire favouring the spread of grasses.
  3. Van Wilgen, B. W., et al. “Response of savanna fire regimes to changing fire‐management policies in a large African national park.” Conservation Biology 18.6 (2004): 1533-1540.  Approaches to fire management in the savanna ecosystems of the 2‐million ha Kruger National Park, South Africa, have changed several times over the past six decades. These approaches have included regular and flexible prescribed burning on fixed areas and a policy that sought to establish a lightning‐dominated fire regime. We sought to establish whether changes in management induced the desired variability in fire regimes over a large area. We used a spatial database of information on all fires in the park between 1957 and 2002 to determine elements of the fire regime associated with each management policy. The area that burned in any given year was independent of the management approach and was strongly related to rainfall (and therefore grass fuels) in the preceding 2 years. On the other hand, management did affect the spatial heterogeneity of fires and their seasonal distribution. Heterogeneity was higher at all scales during the era of prescribed burning, compared with the lightning‐fire interval. The lightning‐fire interval also resulted in a greater proportion (72% vs. 38%) of the area burning in the dry season. Mean fire‐return intervals varied between 5.6 and 7.3 years, and variability in fire‐return intervals was strongly influenced by the sequencing of annual rainfall rather than by management. The attempt at creating a lightning‐dominated fire regime failed because most fires were ignited by humans, and the policy has been replaced by a more pragmatic approach that combines flexible prescribed burning with lightning‐ignited fires.
  4. Beckage, Brian, Louis J. Gross, and William J. Platt. “Modelling responses of pine savannas to climate change and large‐scale disturbance.” Applied Vegetation Science 9.1 (2006): 75-82.  Global warming can potentially influence ecological communities through altered disturbance regimes in addition to increased temperatures. We investigate the response of pine savannas in the southeastern United States to global warming using a simple Lotka‐Volterra competition model together with predicted changes to fire and hurricane disturbance regimes with global climate change. In the southeastern United States, decreased frequency of both fires and hurricanes with global warming will shift pine savannas toward a forested state. A CO2 fertilization effect that increases the growth rate of tree populations will also push southeastern landscapes from open savannas towards closed forests. Transient dynamics associated with climate driven changes in vegetation will last on the order of decades to a century. In our model, the sensitivity of savannas to relative changes in the frequency of fire versus hurricanes is linearly dependent on the growth rate and mortality of trees in fire and hurricane disturbances.
  5. Govender, Navashni, Winston SW Trollope, and Brian W. Van Wilgen. “The effect of fire season, fire frequency, rainfall and management on fire intensity in savanna vegetation in South Africa.” Journal of Applied Ecology 43.4 (2006): 748-758.  Fire is important for the maintenance and conservation of African savanna ecosystems. Despite the importance of fire intensity as a key element of the fire regime, it is seldom measured or included in fire records. We estimated fire intensity in the Kruger National Park, South Africa, by documenting fuel loads, fuel moisture contents, rates of fire spread and the heat yields of fuel in 956 experimental plot burns over 21 years. Individual fires were conducted in five different months (February, April, August, October and December) and at five different return intervals (1, 2, 3, 4 and 6 years). Estimated fire intensities ranged from 28 to 17 905 kW m−1. Fire season had a significant effect on fire intensity. Mean fire intensities were lowest in summer fires (1225 kW m−1), increased in autumn fires (1724 kW m−1) and highest in winter fires (2314 kW m−1); they were associated with a threefold difference between the mean moisture content of grass fuels in winter (28%) and summer (88%). Mean fuel loads increased with post‐fire age, from 2964 kg ha−1 on annually burnt plots to 3972 kg ha−1 on biennial, triennial and quadrennial burnt plots (which did not differ significantly), but decreased to 2881 kg ha−1 on sexennial burnt plots. Fuel loads also increased with increasing rainfall over the previous 2 years. Mean fire intensities showed no significant differences between annual burns and burns in the biennial, triennial and quadrennial categories, despite lower fuel loads in annual burns, suggesting that seasonal fuel moisture effects overrode those of fuel load. Mean fire intensity in sexennial burns was less than half that of other burns (638 vs. 1969 kW m−1). We used relationships between season of fire, fuel loads and fire intensity in conjunction with the park’s fire records to reconstruct broad fire intensity regimes. Changes in management from regular prescribed burning to ‘natural’ fires over the past four decades have resulted in a decrease in moderate‐intensity fires and an increase in high‐intensity fires. The highest fire intensities measured in our study (11 000 – > 17 500 kW m−1) were significantly higher than those previously reported for African savannas, but were similar to those in South American cerrado vegetation. The mean fire intensity for late dry season (winter) fires in our study was less than half that reported for late dry season fires in savannas in northern AustraliaSynthesis and applications. Fire intensity has important effects on savanna vegetation, especially on the dynamics of the tree layer. Fire intensity varies with season (because of differences in fuel moisture) as well as with fuel load. Managers of African savannas can manipulate fire intensity by choosing the season of fire, and further by burning in years with higher or lower fuel loads. The basic relationships described here can also be used to enhance fire records, with a view to building a long‐term data set for the ongoing assessment of the effectiveness of fire management.
  6. Lucas, Chris, et al. “Bushfire weather in southeast Australia: recent trends and projected climate change impacts.” (2007).   [ [FULL TEXT PDF] Bushfires are an inevitable occurrence in Australia. With more than 800 endemic species, Australian vegetation is dominated by fire-adapted eucalypts. Fire is most common over the tropical savannas of the north, where some parts of the land burn on an annual basis. However, the southeast, where the majority of the population resides, is susceptible to large wildfires that threaten life and property. A unique factor in these fires of the southeast is the climate of the region. The southeast experiences a so-called Mediterranean climate, with hot, dry summers and mild, wet winters. The winter and spring rains allow fuel growth, while the dry summers allow fire danger to build. This normal risk is exacerbated by periodic droughts that occur as a part of natural interannual climate variability. Climate change projections indicate that southeastern Australia is likely to become hotter and drier in future. A study conducted in 2005 examined the potential impacts of climate change on fire- eather at 17 sites in southeast Australia. It found that the number of ‘very high’ and ‘extreme’ fire danger days could increase by 4-25% by 2020 and 15-70% by 2050. Tasmania was an exception, showing little increase. This report updates the findings of the 2005 study. A wider range of observations is analysed, with additional sites in New South Wales, South Australia and southeast Queensland included. The baseline dates of the study, commencing in 1973, are extended to include the 2006-07 fire season. The estimated effects of climate change by 2020 and 2050 are recalculated using updated global warming projections from the Intergovernmental Panel on Climate Change (IPCC). Two new fire danger categories are considered: ‘very extreme’ and ‘catastrophic’. This study also differs from the 2005 study in that different analysis methods are used. In addition to the annual changes in fire danger estimated before, changes to individual seasons and season lengths are explicitly examined. There is also a focus on the changes to the upper extremes of fire danger. These projected changes are compared with trends over the past few decades. Climate change projections: The primary source of data for this study is the standard observations made by the Bureau of Meteorology. The locations of the 26 selected observing stations are shown in Figure E1. At these stations, the historical record of Forest Fire Danger index (FFDI) and the likely impacts of future climate change are calculated. There are homogenization issues with the data that could affect the interpretation of the results, particularly the analysis of the current trends. However, estimates of the errors suggest that these are small enough that we can have confidence in the results. Climate change projections over southeastern Australia were generated from two CSIRO climate simulations named CCAM (Mark2) and CCAM (Mark3). Projected changes in daily temperature, humidity, wind and rainfall were generated for the years 2020 and 2050, relative to 1990 (the reference year used by the IPCC). These projections include changes in daily variability. They are expressed as a pattern of change per degree of global warming.
  7. Whitehead, Peter J., et al. “The management of climate change through prescribed savanna burning: emerging contributions of indigenous people in northern Australia.” Public Administration and Development: The International Journal of Management Research and Practice 28.5 (2008): 374-385.  Australia has committed to substantial cuts in greenhouse gas emissions (GHGE) achieved through a national emissions trading system, raising important issues for relatively undeveloped regions of Northern Australia and, in particular, Indigenous lands. Can mostly Indigenous and socio‐economically disadvantaged people living in such regions develop institutions to contribute significantly to the mitigation of GHGE, yet pursue regional development? Will national policies adequately recognise the special needs and potential contributions of such communities? These questions and the challenges inherent in them are addressed in this article with reference to a significant initiative involving the community management of landscape fire to reduce annual GHGE from savanna burning. This initiative appears to offer potential for engagement with global carbon markets, but it will need local, national and international support, along with appropriate changes in attitudes and legal arrangements, to ensure an equitable distribution of tangible rewards, while protecting the cultural and related benefits of customary fire use. Copyright © 2008 John Wiley & Sons, Ltd.
  8. Van Der Werf, Guido R., et al. “Climate controls on the variability of fires in the tropics and subtropics.” Global Biogeochemical Cycles 22.3 (2008).  In the tropics and subtropics, most fires are set by humans for a wide range of purposes. The total amount of burned area and fire emissions reflects a complex interaction between climate, human activities, and ecosystem processes. Here we used satellite‐derived data sets of active fire detections, burned area, precipitation, and the fraction of absorbed photosynthetically active radiation (fAPAR) during 1998–2006 to investigate this interaction. The total number of active fire detections and burned area was highest in areas that had intermediate levels of both net primary production (NPP; 500–1000 g C m−2 year−1) and precipitation (1000–2000 mm year−1), with limits imposed by the length of the fire season in wetter ecosystems and by fuel availability in drier ecosystems. For wet tropical forest ecosystems we developed a metric called the fire‐driven deforestation potential (FDP) that integrated information about the length and intensity of the dry season. FDP partly explained the spatial and interannual pattern of fire‐driven deforestation across tropical forest regions. This climate‐fire link in combination with higher precipitation rates in the interior of the Amazon suggests that a negative feedback on fire‐driven deforestation may exist as the deforestation front moves inward. In Africa, compared to the Amazon, a smaller fraction of the tropical forest area had FDP values sufficiently low to prevent fire use. Tropical forests in mainland Asia were highly vulnerable to fire, whereas forest areas in equatorial Asia had, on average, the lowest FDP values. FDP and active fire detections substantially increased in forests of equatorial Asia, however, during El Niño periods. In contrast to these wet ecosystems we found a positive relationship between precipitation, fAPAR, NPP, and active fire detections in arid ecosystems. This relationship was strongest in northern Australia and arid regions in Africa. Highest levels of fire activity were observed in savanna ecosystems that were limited neither by fuel nor by the length of the fire season. However, relations between annual precipitation or drought extent and active fire detections were often poor here, hinting at the important role of other factors, including land managers, in controlling spatial and temporal variability of fire.
  9. Roy, David P., et al. “The collection 5 MODIS burned area product—Global evaluation by comparison with the MODIS active fire product.” Remote sensing of Environment 112.9 (2008): 3690-3707.  The results of the first consecutive 12 months of the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) global burned area product are presented. Total annual and monthly area burned statistics and missing data statistics are reported at global and continental scale and with respect to different land cover classes. Globally the total area burned labeled by the MODIS burned area product is 3.66 × 106 km2 for July 2001 to June 2002 while the MODIS active fire product detected for the same period a total of 2.78 × 106 km2, i.e., 24% less than the area labeled by the burned area product. A spatio-temporal correlation analysis of the two MODIS fire products stratified globally for pre-fire leaf area index (LAI) and percent tree cover ranges indicate that for low percent tree cover and LAI, the MODIS burned area product defines a greater proportion of the landscape as burned than the active fire product; and with increasing tree cover (> 60%) and LAI (> 5) the MODIS active fire product defines a relatively greater proportion. This pattern is generally observed in product comparisons stratified with respect to land cover. Globally, the burned area product reports a smaller amount of area burned than the active fire product in croplands and evergreen forest and deciduous needleleaf forest classes, comparable areas for mixed and deciduous broadleaf forest classes, and a greater amount of area burned for the non-forest classes. The reasons for these product differences are discussed in terms of environmental spatio-temporal fire characteristics and remote sensing factors, and highlight the planning needs for MODIS burned area product validation.
  10. Archibald, Sally, et al. “What limits fire? An examination of drivers of burnt area in Southern Africa.” Global Change Biology 15.3 (2009): 613-630.  The factors controlling the extent of fire in Africa south of the equator were investigated using moderate resolution (500 m) satellite‐derived burned area maps and spatial data on the environmental factors thought to affect burnt area. A random forest regression tree procedure was used to determine the relative importance of each factor in explaining the burned area fraction and to address hypotheses concerned with human and climatic influences on the drivers of burnt area. The model explained 68% of the variance in burnt area. Tree cover, rainfall in the previous 2 years, and rainfall seasonality were the most important predictors. Human activities – represented by grazing, roads per unit area, population density, and cultivation fraction – were also shown to affect burnt area, but only in parts of the continent with specific climatic conditions, and often in ways counter to the prevailing wisdom that more human activity leads to more fire. The analysis found no indication that ignitions were limiting total burnt area on the continent, and most of the spatial variation was due to variation in fuel load and moisture. Split conditions from the regression tree identified (i) low rainfall regions, where fire is rare; (ii) regions where fire is under human control; and (iii) higher rainfall regions where burnt area is determined by rainfall seasonality. This study provides insights into the physical, climatic, and human drivers of fire and their relative importance across southern Africa, and represents the beginnings of a predictive framework for burnt area.
  11. Archibald, Sally, et al. “Climate and the inter‐annual variability of fire in southern Africa: a meta‐analysis using long‐term field data and satellite‐derived burnt area data.” Global Ecology and Biogeography 19.6 (2010): 794-809.  This study investigates inter‐annual variability in burnt area in southern Africa and the extent to which climate is responsible for this variation. We compare data from long‐term field sites across the region with remotely sensed burnt area data to test whether it is possible to develop a general model. Location Africa south of the equator. Methods Linear mixed effects models were used to determine the effect of rainfall, seasonality and fire weather in driving variation in fire extent between years, and to test whether the effect of these variables changes across the subcontinent and in areas more and less impacted by human activities. Results A simple model including rainfall and seasonality explained 40% of the variance in burnt area between years across 10 different protected areas on the subcontinent, but this model, when applied regionally, indicated that climate had less impact on year‐to‐year variation in burnt area than would be expected. It was possible to demonstrate that the relative importance of rainfall and seasonality changed as one moved from dry to wetter systems, but most noticeable was the reduction in climatically driven variability of fire outside protected areas. Inter‐annual variability is associated with the occurrence of large fires, and large fires are only found in areas with low human impact. Main conclusions This research gives the first data‐driven analysis of fire–climate interactions in southern Africa. The regional analysis shows that human impact on fire regimes is substantial and acts to limit the effect of climate in driving variation between years. This is in contrast to patterns in protected areas, where variation in accumulated rainfall and the length of the dry season influence the annual area burnt. Global models which assume strong links between fire and climate need to be re‐assessed in systems with high human impact.
  12. Archibald, Sally, et al. “Southern African fire regimes as revealed by remote sensing.” International Journal of Wildland Fire 19.7 (2010): 861-878.  Here we integrate spatial information on annual burnt area, fire frequency, fire seasonality, fire radiative power and fire size distributions to produce an integrated picture of fire regimes in southern Africa. The regional patterns are related to gradients of environmental and human controls of fire, and compared with findings from other grass-fuelled fire systems on the globe. The fire regime differs across a gradient of human land use intensity, and can be explained by the differential effect of humans on ignition frequencies and fire spread. Contrary to findings in the savannas of Australia, there is no obvious increase in fire size or fire intensity from the early to the late fire season in southern Africa, presumably because patterns of fire ignition are very different. Similarly, the importance of very large fires in driving the total annual area burnt is not obvious in southern Africa. These results point to the substantial effect that human activities can have on fire in a system with high rural population densities and active fire management. Not all aspects of a fire regime are equally impacted by people: fire-return time and fire radiative power show less response to human activities than fire size and annual burned area.
  13. Heckbert, Scott, et al. “Indigenous Australians fight climate change with fire.” Solutions: For A Sustainable & Desirable Future (2011).  The article focuses on the move of Indigenous people in Australia to implement fire management in an effort to improve landscape condition and reduce greenhouse gas emissions. It highlights the launch of the West Arnhem Land Fire Abatement (WALFA) project, a prime example of scientists, governments, Indigenous land managers, and carbon markets connecting to offer innovative solutions to resource management and economic development. It also highlights ecosystem services in the region.
  14. Bachelet, Dominique, et al. “Climate change impacts on western Pacific Northwest prairies and savannas.” Northwest Science 85.2 (2011): 411-429.  This paper represents a collaboration by conservation practitioners, ecologists, and climate change scientists to provide specific guidance on local and regional adaptation strategies to climate change for conservation planning and restoration activities. Our geographic focus is the Willamette Valley-Puget Trough-Georgia Basin (WPG) ecoregion, comprised of valley lowlands formerly dominated by now-threatened prairies and oak savannas. We review climate model strengths and limitations, and summarize climate change projections and potential impacts on WPG prairies and oak savannas. We identify a set of six climate-smart strategies that do not require abandoning past management approaches but rather reorienting them towards a dynamic and uncertain future. These strategies focus on linking local and regional landscape characteristics to the emerging needs of species, including potentially novel species assemblages, so that prairies and savannas are maintained in locations and conditions that remain well-suited to their persistence. At the regional scale, planning should use the full range of biological and environmental variability. At the local scale, habitat heterogeneity can be used to support species persistence by identifying key refugia. Climate change may marginalize sites currently used for agriculture and forestry, which may become good candidates for restoration. Native grasslands may increasingly provide ecosystem services that may support broader societal needs exacerbated by climate change. Judicious monitoring can help identify biological thresholds and restoration opportunities. To prepare for both future challenges and opportunities brought about by climate change, land managers must incorporate climate change projections and uncertainties into their long-term planning.
  15. Staver, A. Carla, Sally Archibald, and Simon Levin. “Tree cover in sub‐Saharan Africa: rainfall and fire constrain forest and savanna as alternative stable states.” Ecology 92.5 (2011): 1063-1072.  Savannas are known as ecosystems with tree cover below climate‐defined equilibrium values. However, a predictive framework for understanding constraints on tree cover is lacking. We present (a) a spatially extensive analysis of tree cover and fire distribution in sub‐Saharan Africa, and (b) a model, based on empirical results, demonstrating that savanna and forest may be alternative stable states in parts of Africa, with implications for understanding savanna distributions. Tree cover does not increase continuously with rainfall, but rather is constrained to low (<50%, “savanna”) or high tree cover (>75%, “forest”). Intermediate tree cover rarely occurs. Fire, which prevents trees from establishing, differentiates high and low tree cover, especially in areas with rainfall between 1000 mm and 2000 mm. Fire is less important at low rainfall (<1000 mm), where rainfall limits tree cover, and at high rainfall (>2000 mm), where fire is rare. This pattern suggests that complex interactions between climate and disturbance produce emergent alternative states in tree cover. The relationship between tree cover and fire was incorporated into a dynamic model including grass, savanna tree saplings, and savanna trees. Only recruitment from sapling to adult tree varied depending on the amount of grass in the system. Based on our empirical analysis and previous work, fires spread only at tree cover of 40% or less, producing a sigmoidal fire probability distribution as a function of grass cover and therefore a sigmoidal sapling to tree recruitment function. This model demonstrates that, given relatively conservative and empirically supported assumptions about the establishment of trees in savannas, alternative stable states for the same set of environmental conditions (i.e., model parameters) are possible via a fire feedback mechanism. Integrating alternative stable state dynamics into models of biome distributions could improve our ability to predict changes in biome distributions and in carbon storage under climate and global change scenarios.
  16. Price, Owen F., Jeremy Russell-Smith, and Felicity Watt. “The influence of prescribed fire on the extent of wildfire in savanna landscapes of western Arnhem Land, Australia.” International Journal of Wildland Fire 21.3 (2012): 297-305.  Fire regimes in many north Australian savanna regions are today characterised by frequent wildfires occurring in the latter part of the 7-month dry season. A fire management program instigated from 2005 over 24 000 km2 of biodiversity-rich Western Arnhem Land aims to reduce the area and severity of late dry-season fires, and associated greenhouse gas emissions, through targeted early dry-season prescribed burning. This study used fire history mapping derived mostly from Landsat imagery over the period 1990–2009 and statistical modelling to quantify the mitigation of late dry-season wildfire through prescribed burning. From 2005, there has been a reduction in mean annual total proportion burnt (from 38 to 30%), and particularly of late dry-season fires (from 29 to 12.5%). The slope of the relationship between the proportion of early-season prescribed fire and subsequent late dry-season wildfire was ~–1. This means that imposing prescribed early dry-season burning can substantially reduce late dry-season fire area, by direct one-to-one replacement. There is some evidence that the spatially strategic program has achieved even better mitigation than this. The observed reduction in late dry-season fire without concomitant increase in overall area burnt has important ecological and greenhouse gas emissions implications. This efficient mitigation of wildfire contrasts markedly with observations reported from temperate fire-prone forested systems.
  17. Archibald, Sally, A. Carla Staver, and Simon A. Levin. “Evolution of human-driven fire regimes in Africa.” Proceedings of the National Academy of Sciences 109.3 (2012): 847-852.  Human ability to manipulate fire and the landscape has increased over evolutionary time, but the impact of this on fire regimes and consequences for biodiversity and biogeochemistry are hotly debated. Reconstructing historical changes in human-derived fire regimes empirically is challenging, but information is available on the timing of key human innovations and on current human impacts on fire; here we incorporate this knowledge into a spatially explicit fire propagation model. We explore how changes in population density, the ability to create fire, and the expansion of agropastoralism altered the extent and seasonal distribution of fire as modern humans arose and spread through Africa. Much emphasis has been placed on the positive effect of population density on ignition frequency, but our model suggests this is less important than changes in fire spread and connectivity that would have occurred as humans learned to light fires in the dry season and to transform the landscape through grazing and cultivation. Different landscapes show different limitations; we show that substantial human impacts on burned area would only have started ∼4,000 B.P. in open landscapes, whereas they could have altered fire regimes in closed/dissected landscapes by ∼40,000 B.P. Dry season fires have been the norm for the past 200–300 ky across all landscapes. The annual area burned in Africa probably peaked between 4 and 40 kya. These results agree with recent paleocarbon studies that suggest that the biomass burned today is less than in the recent past in subtropical countries.
  18. Russell-Smith, Jeremy, et al. “Managing fire regimes in north Australian savannas: applying Aboriginal approaches to contemporary global problems.” Frontiers in Ecology and the Environment 11.s1 (2013): e55-e63. Savannas constitute the most fire‐prone biome on Earth and annual emissions from savanna‐burning activities are a globally important source of greenhouse‐gas (GHG) emissions. Here, we describe the application of a commercial fire‐management program being implemented over 28 000 km2 of savanna on Aboriginal lands in northern Australia. The project combines the reinstatement of Aboriginal traditional approaches to savanna fire management – in particular a strategic, early dry‐season burning program – with a recently developed emissions accounting methodology for savanna burning. Over the first 7 years of implementation, the project has reduced emissions of accountable GHGs (methane, nitrous oxide) by 37.7%, relative to the pre‐project 10‐year emissions baseline. In addition, the project is delivering social, biodiversity, and long‐term biomass sequestration benefits. This methodological approach may have considerable potential for application in other fire‐prone savanna settings. Savannas – defined broadly as tropical and subtropical grasslands (characterized by grasses with C4 photosynthetic pathway) with varying densities of tree cover – constitute the most fire‐prone ecosystems on Earth. They occupy one‐sixth of the planet’s land surface and support a tenth of the human population, and while rates of land‐use change are uncertain, these systems are likely to experience twice the rate of conversion as compared to tropical forests (White et al. 2000Grace et al. 2006). Almost 60% of savannas, and two‐thirds of the human populations that live in these areas, are located in sub‐Saharan Africa, with other major occurrences (in order of geographic extent) in Australia, South America, and Asia (White et al. 2000Lehmann et al. 2011). The deliberate burning of savannas, for a variety of agricultural, pastoral, and traditional management purposes, contributes as much as 10% of annual total global carbon (C) emissions and 44% of estimated C emissions from all sources of biomass burning (IPCC 2007van der Werf et al. 2010). Savannas constitute the most fire‐prone biome in the world. Although officially banned by government regulations in many countries, use of fire plays important roles in a range of savanna livelihood and biodiversity management applications. This paper discusses the application of a novel fire‐management project being undertaken by Aboriginal people in northern Australia that reduces greenhouse gas emissions from savanna fires.  [FULL TEXT]
  19. Pitman, ARCCSS Director Prof Andy. “Links between global warming and NSW bush fires.”  Submitted by astone on Fri, 10/25/2013 – 11:11, by ARCCSS Director Prof Andy Pitman:  A great deal has been said about the recent New South Wales bush fires and whether there is a link between these bush fires and global warming. An attempt to explain what is and is not known is provided here.First, some context setting. Bush fires have occurred in Australia for a long time. There is a history of fire in Australia exceeding 400,000 years with high variability in fire frequency associated with natural climate variability (Kershaw et al. 2002). A substantial increase in fire frequency occurred about 38,000 years ago. This was probably related to human activity given that there is little evidence for a coincident change in climate. A second peak in fire occurrence was associated with European settlement in 1788 (Kershaw et al. 2002). Currently, around 5% of the Australian land surface is burned annually consuming approximately 10% of the net primary productivity of the continent (Pittock 2003). So, fire is a natural phenomenon in Australia and a specific fire event as seen in the Blue Mountains in the last week is not caused by global warming. I am not aware of anyone who says it is. The questions are more around whether global warming is increasing the risk of bush fires, did global warming make the recent fires more likely and therefore whether there is a global warming link to the fires in the Blue Mountains. The risk of bush fire is driven by the amount and dryness of fuel, ambient weather and ignitions (Archibald et al., 2009). That is, you need fuel, you need hot and dry conditions and you need an ignition source. I’ll deal with what we know for each of these in turn. [FULL TEXT]

 

5 Responses to "AGW Bushfires of 2019-2020: Bibliography"

Thank you sir, as always

[…] AGW Bushfires of 2019-2020: Bibliography The Ocean Heat Waves of AGW […]

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