Widespread Wildfires Research Articles

Enhanced magnetization of the Marlboro Clay as a product of soil pyrogenesis at the Paleocene–Eocene boundary?

The kaolinite-rich Marlboro Clay was deposited on the inner shelf in the Salisbury Embayment of the U.S. Atlantic margin at the onset of the carbon isotope excursion marking the 56 Ma Paleocene–Eocene boundary and is characterized by an anomalously high concentration of magnetic nanoparticles of enigmatic origin that give rise to notably intense bulk magnetization. Recent studies point to a magnetic assemblage that is dominated by single-domain magnetite particles that tend to be isolated rather than arranged in chains, the most distinguishing feature of magnetotactic bacteria fossils. On the other hand, it is very unlikely that the nanoparticles can be condensates of an impact plume given the meter-scale thickness of the Marlboro Clay. We obtained new data from a landward proximal site at Wilson Lake on the New Jersey Coastal Plain and find that the abrupt increase in magnetite nanoparticles is virtually coincident stratigraphically with the recently reported impact spherule layer at the base of the Marlboro Clay in the same core. Yet the high field magnetic susceptibility, a measure of total iron concentration, and strontium isotope values on bulk sediment, an indicator of sediment weathering provenance, are not different in the Marlboro Clay from the immediately underlying Vincentown Formation. We suggest that the distinctive magnetic properties of the Marlboro Clay originated from pyromagnetic soil enhancement by widespread wildfires on the adjoining drainage area. The pyrogenetic products were soon washed from the denuded landscape and rapidly deposited as mud-waves across the shelf, becoming the Marlboro Clay. A few percent of incinerated biomass ends up as calcite known as wood ash stone and can inherit its light carbon isotope composition. Disseminated wood ash stone entrained in the Marlboro Clay could contribute to the landward increase in amplitude of the carbon isotope excursion in bulk carbonate data. A plausible trigger for the initial conflagration is a fireball from the impact of a sizable extraterrestrial object at moderate range.

Evidence of widespread wildfires in a coal seam from the middle Permian of the North China Basin

The North China Basin is the largest coal-bearing basin in China, and has an areal extent of 800,000 km2. We analyzed 138 coal samples and in situ pillar coal samples of the middle Permian from this basin by macropetrography, microscope, scanning electron microscope, gas chromatography, and gas chromatography–mass spectrometer in order to study wildfires. High contents of inertinite (charcoal) and natural coke particles observed in coal samples indicate that vegetation in precursor mires and peats of the middle Permian coal from north China was exposed to far-ranging wildfires. In addition, high-molecular-weight polycyclic aromatic hydrocarbons were detected in the coal samples. These aromatic compounds were formed under high temperatures and provide further evidence of wildfire. These wildfires would have discharged significant CO and CO2 gases into the atmosphere and affected the paleoclimate and paleoecosystem.

Accounting for hominins’ fast exit from Africa (“The Out of Africa Event 1”) due to widespread wildfires, accidently and inevitably ignited by them, c.a. 1.8 – 1.6 mya

Accounting for hominins’ fast exit from Africa (“The Out of Africa Event 1”) due to widespread wildfires, accidently and inevitably ignited by them, c.a. 1.8 – 1.6 mya Michael Iannicelli Abstract An established hypothesis explaining “The Out of Africa Event1” says that the cold climate or very arid conditions of the Pleistocene Epoch were most probably the driving-force of the H. erectus‟ migration out of Africa and into Eurasia, 1.8 – 1.6 mya, but a perspective is offered here which blames frequent, lightning-strikes and misusage of fire by hominins as the agents that led to uncontrolled, widespread wildfires. Paleo-winds advanced the wildfires according to wind direction, thus intensifying the widespread threat to the chagrin of the hominins. A Pleistocene, temporary, land bridge, enabled some hominins to escape the threat of widespread wildfires by allowing them to cross over from east Africa to Eurasia. One anomaly noted is that either the wildfires or some vast impediment prevented H. erectus from climbing latitudinal lines to north Africa at that time, but that delay to the mid-latitudes may have ended coincidently with Eurasian travel on the eastern coastline of the juxtaposed Red Sea. The sea would have acted as a natural fire-retardant allowing hominins to finally move up to the mid-latitudes. The northbound migration would have also forced tropically-derived hominins to quickly adapt to environmental change and low temperatures while a rationalization is proposed concerning how they may have tackled their newest challenges. Full Text: PDF DOI: 10.15640/jaa.v5n2a4

Cumulative Effects of Environmental Change on Culturally Significant Ecosystems in the Inuvialuit Settlement Region + Supplementary Appendices 1 to 3 (See Article Tools)

The Inuvialuit Settlement Region (ISR) in the western Canadian Arctic is experiencing environmental changes that affect subsistence harvesting practices and are of concern to local communities. In order to assess the impacts of multiple disturbances on culturally important ecosystems in the ISR, we created a cumulative disturbance map that represents relative intensity of terrestrial disturbances across the study region. We then assessed the relative level of environmental disturbance in important harvesting areas and management zones. Subsequently, we modeled nine future disturbance scenarios that included combinations of increased human impacts and more frequent and widespread wildfires. Using the conservation planning software Marxan, we assessed the potential to conserve large, contiguous areas of unaffected harvesting lands across all scenarios. Our results show that important management zones, wildlife harvesting areas, and community planning zones are all affected by environmental disturbances. Marxan optimizations show that existing disturbance levels create thresholds for current conservation potential and indicate that future disturbances will further limit conservation potential. These results suggest that conservation planners in the region must take steps to anticipate more widespread natural and human-caused disturbance in the ISR and work to maintain large contiguous landscapes that can support wildlife harvesting in the face of ongoing environmental disturbance.

Air quality in Singapore during the 2013 smoke-haze episode over the Strait of Malacca: Lessons learned

The widespread wildfires that raged across Indonesia's island of Sumatra in June 2013 triggered the worst air pollution episode ever recorded in Singapore. The highest 24-h moving average PM2.5 concentration reported by the authorities reached a whopping 310μgm−3 on June 20, 2013. However, a top 3-h moving average Pollutant Standard Index (PSI) of 401 (index ceiling is 500) based only in PM10 concentration data occurred the following day, and a maximum 24-h moving average PSI of 246 with an associated 24-h PM10 concentration of 382μgm−3 was reported on June 22, 2013. The decoupling between these air quality health advisories evidences the flaw in informing to the public on the hour when the air quality was at its worst. Up until now, despite the positive changes on the public dissemination of air quality information, the real hourly pollution levels experienced in Singapore during the 2013 smoke-haze episode are still unknown. To unveil the hourly PM2.5 concentrations this work applies a set of statistical models to the available air quality data during the episode and the lately 1-h PM2.5 concentration records published since April 2014 on a day-by-day bases. Results suggest maximum likelihood hourly PM2.5 concentrations over 600μgm−3, twice the maximum 24-h moving average reported by the authorities.

Seedbank dynamics after masting in mulga (Acacia aptaneura): Implications for post-fire regeneration

Members of the arid Australian mulga (Acacia aneura) complex are fire-sensitive shrubs that produce mast seed crops after exceptionally high rainfall years. Such years also drive widespread wildfires in inland Australia, as high rainfall causes grassy fuels to accumulate, thereby enabling fuel contiguity to occur. Despite seedling regeneration playing an important role in mulga post-fire recovery, a dearth of information exists on the dynamics of its seedbanks. Here we examine the temporal and spatial dynamics of mulga seedbanks after a region-wide masting event at Laycock's Sandplain, central Australia. Masting had a profound effect on seedbanks, producing massive but short-lived pulses of seed in upper soil layers. After seed fall, seedbanks declined rapidly, and within 18 months had been reduced by predator depredations to low pre-mast levels. Our results suggest that mulga masting should enhance resilience to burning by providing transient seed pulses during periods of high flammability (i.e. after heavy rainfalls). The results also suggest that burn intensity will influence post-fire regeneration, by interacting with seed germination biology and post-mast seedbank dynamics. In our discussion, we examine possible evolutionary drivers behind mulga seeding periodicity, and hypothesize that rain-driven masting in mulga is a fire-related form of environmentally predictive masting.

Climatic influences on fire regimes in ponderosa pine forests of the Zuni Mountains, NM, USA

We characterized fire history and examined climate–fire relationships in dry ponderosa pine (Pinus ponderosa) forests in the Zuni Mountains of northwestern New Mexico. Our findings indicate that the historical wildfire regime for the study area was typified by high-frequency, low-severity surface fires. Climate–wildfire relationships were assessed using both Superposed Epoch Analysis (SEA) and Bivariate Event Analysis (BEA). SEA revealed that interannual variability of the El Niño–Southern Oscillation (ENSO) and the Palmer Drought Severity Index (PDSI) was a strong driver of widespread wildfires; wetter conditions often occurred one to two years prior to fire and were followed by drought during the fire year. BEA revealed statistically significant relationships only in the case of extreme PDSI events and widespread wildfire in the year of fire (t=0). No relationship was found between either the Pacific Decadal Oscillation (PDO) or the Atlantic Multidecadal Oscillation (AMO) and widespread fire occurrence, signifying that shorter-term (i.e. interannual) oscillations between wet and dry conditions, rather than longer-term climatic variability, were historically most conducive to fire. Contextualizing these findings under ongoing climate and land-use change is challenging. Full restoration to historical conditions may be neither possible nor desired, but targeted efforts to promote a frequent, low-severity wildfire regime are generally consistent with our understanding of historical fire activity in this forest type and may foster ecological, economic, and/or societal goals.

Assessing possible shifts in wildfire regimes under a changing climate in mountainous landscapes

Climate change may affect the probability of extreme events such as wildfires. Although wildfires are some of the most important ecological processes in forest ecosystems, large-scale wildfires are often perceived as an environmental disaster. Since failure to include the dynamic nature of ecosystems in planning will inevitably lead to unexpected outcomes, we need to enhance our ability to cope with future extreme events coupled with climate change. This study presents several future scenarios in three different time periods for Canada’s Columbia Montane Cordillera Ecoprovince, which is prone to wildfires. These scenarios predict the probability of occurrence of widespread wildfires based on the hierarchical Bayesian model. The model was based on the relationships between wildfires and the Monthly Drought Code (MDC). The MDC is a generalized monthly version of the Daily Drought Code widely used across Canada by forest fire management agencies for monitoring of wildfire risk. To calculate future MDC values, we relied on different possible future conditions of climate, given by the Global Circulation Models. We found a regime shift in drought intensity with abrupt decreases in lightning-caused wildfire activity around 1940, suggesting that future wildfire risks can be inferred primarily from the summer drought code. For future periods, we found increasing trends in the probabilities of large-scale fires with time in most areas. It should be notable that, by the 2080s, there is a probability of some areas having more than 50% of large-scale wildfires under the “average” climatic conditions in the future, indicating that, even without “extreme” weather conditions, some ecosystems will have a fundamental probability of experiencing catastrophic fires under the condition of average summer. However, the rate of progression toward a fire-prone condition is quite different among the three climate change scenarios and among the region analyzed. Given such scenario-sensitive, spatially-heterogeneous patterns of wildfire probability in response to climate variability, management strategy should be flexible and more localized. By drawing on this knowledge, it may be possible to mitigate climate change impacts both before they arise and once they have occurred. These considerations are critical for maintaining the integrity of systems shaped by large-scale natural disturbances to increase their resilience to the changing climate while protecting human society and infrastructures. Working with alternative scenarios will facilitate our adaptation to climate change in managing fire-prone forest ecosystems.

Soil Seed Banks of the Exotic Annual Grass Bromus rubens on a Burned Desert Landscape

Red brome (Bromus rubens), an exotic annual grass, can dominate soil seed banks and poses serious threats to mature native plant communities in the Mojave Desert by competing with native species and providing fine fuels that facilitate widespread wildfire. By exploring how seed bank density and composition in burned areas change over time since fire (TSF), we can improve our understanding of how the seed banks are affected by fire. Samples of the 5-cm-deep soil seed bank were collected from two microsites (under shrubs, in open interspaces) within paired burned and unburned areas on 12 fires ranging from 5–31yr TSF. Seed bank samples were assayed using the emergence method and seed densities were compared among TSFs, burn status (burned, unburned), and microsites for the species that emerged. Red brome soil seed bank density was spatially variable and TSF rarely predicted abundance. Overall, undershrub seed densities did not differ between burned and unburned areas. However, at some fire sites, seed densities in interspaces were greater in burned than unburned areas. Although native seed densities were low overall, they did not appear to differ according to burn status. Studies have shown that red brome plant and seed bank densities can be greatly reduced immediately after fire. Management efforts that focus on this initial colonization window may be able to take advantage of diminished red brome seed densities to limit its reestablishment while facilitating the establishment of native species. However, this window is brief, as our findings indicate that once reestablished, red brome soil seed densities in burned areas can be similar to those in unburned areas within 5yr.

Fire Severity Filters Regeneration Traits to Shape Community Assembly in Alaska’s Boreal Forest

Disturbance can both initiate and shape patterns of secondary succession by affecting processes of community assembly. Thus, understanding assembly rules is a key element of predicting ecological responses to changing disturbance regimes. We measured the composition and trait characteristics of plant communities early after widespread wildfires in Alaska to assess how variations in disturbance characteristics influenced the relative success of different plant regeneration strategies. We compared patterns of post-fire community composition and abundance of regeneration traits across a range of fire severities within a single pre-fire forest type– black spruce forests of Interior Alaska. Patterns of community composition, as captured by multivariate ordination with nonmetric multidimensional scaling, were primarily related to gradients in fire severity (biomass combustion and residual vegetation) and secondarily to gradients in soil pH and regional climate. This pattern was apparent in both the full dataset (n = 87 sites) and for a reduced subset of sites (n = 49) that minimized the correlation between site moisture and fire severity. Changes in community composition across the fire-severity gradient in Alaska were strongly correlated to variations in plant regeneration strategy and rooting depth. The tight coupling of fire severity with regeneration traits and vegetation composition after fire supports the hypothesis that disturbance characteristics influence patterns of community assembly by affecting the relative success of different regeneration strategies. This study further demonstrated that variations in disturbance characteristics can dominate over environmental constraints in determining early patterns of community assembly. By affecting the success of regeneration traits, changes in fire regime directly shape the outcomes of community assembly, and thus may override the effects of slower environmental change on boreal forest composition.

Synchronous Wildfire Activity Rise and Mire Deforestation at the Triassic–Jurassic Boundary

The end-Triassic mass extinction event (∼201.4 million years ago) caused major faunal and floral turnovers in both the marine and terrestrial realms. The biotic changes have been attributed to extreme greenhouse warming across the Triassic–Jurassic (T–J) boundary caused by massive release of carbon dioxide and/or methane related to extensive volcanism in the Central Atlantic Magmatic Province (CAMP), resulting in a more humid climate with increased storminess and lightning activity. Lightning strikes are considered the primary source of wildfires, producing charcoal, microscopically recognized as inertinite macerals. The presence of polycyclic aromatic hydrocarbons (PAHs) of pyrolytic origin and allochthonous charcoal in siliciclastic T–J boundary strata has suggested widespread wildfire activity at the time. We have investigated largely autochthonous coal and coaly beds across the T–J boundary in Sweden and Denmark. These beds consist of predominantly organic material from the in situ vegetation in the mires, and as the coaly beds represent a substantial period of time they are excellent environmental archives. We document a remarkable increase in inertinite content in the coal and coaly beds across the T–J boundary. We show estimated burning temperatures derived from inertinite reflectance measurements coupled with palynological data and conclude that pre-boundary late Rhaetian mire wildfires included high-temperature crown fires, whereas latest Rhaetian–Sinemurian mire wildfires were more frequent but dominated by lower temperature surface fires. Our results suggest a major change in the mire ecosystems across the T–J boundary from forested, conifer dominated mires to mires with a predominantly herbaceous and shrubby vegetation. Contrary to the overall regional vegetation for which onset of recovery commenced in the early Hettangian, the sensitive mire ecosystem remained affected during the Hettangian and did not start to recover until around the Hettangian–Sinemurian boundary. Decreasing inertinite content through the Lower Jurassic suggests that fire activity gradually resumed to considerable lower levels.

Wildfire Consumption and Interannual Impacts by Land Cover in Alaskan Boreal Forest

AbstractBoreal forest fires are an important source of terrestrial carbon emissions, particularly during years of widespread wildfires. Most carbon emission models parameterize wildfire impacts and carbon flux to area burned by fires, therein making the assumption that fires consume a spatiotemporally homogeneous landscape composed of predominantly spruce forests and peat bogs with deep duff layers. While recent efforts have demonstrated that boreal forest fires heterogeneously consume aboveground vegetation, little remains known about the vegetation consumed during such fires. We examined climate, land cover, area burned, and fire impacts for large fires (2002 to 2009) across the Alaskan boreal landscape to address the validity of assumptions made by carbon emissions models for boreal fires. Results indicated that while coniferous vegetation, particularly spruce forests and spruce bogs, comprised the majority of the area burned in all years, shrub land cover comprised a substantial proportion (up to 35 %) of the area burned during warmer years of the study period. Interannual climate variability significantly influenced both the proportion of vegetation classes burned and the distribution of fire impacts across years and vegetation classes. We found that surface fuel modifications were sensitive to both the vegetation type that burned and climatic conditions. Area burned is an inadequate input metric for increasingly refined carbon emissions models, and consideration of heterogeneous fire impacts may improve carbon emissions modeling.

Research Spotlight: Deadly 2010 Russian heat wave not a consequence of climate change

Although some people may try to ascribe specific extreme weather events to climate change, global warming cannot be held responsible for recent weather events such as the 2010 Russian heat wave. Using climate simulations and a comparison against historical conditions, Dole et al. assess the influence of greenhouse gases, aerosols, anomalous sea surface temperatures, and other potential climate forcings on the likelihood and magnitude of the 2010 Russian heat wave. The authors suggest that the heat wave—which lasted from late June to mid‐August and was responsible for thousands of deaths, widespread wildfires, and devastating crop loss—fell well within the bounds of natural climate variability. The authors find that none of the tested climate factors showed appreciable ability to predict the extreme temperatures seen throughout the heat wave. Additionally, the researchers' historical analysis revealed that July temperatures, as well as the temperature variability, for the affected region of western Russia showed no significant trend over the past 130 years. They note that the top 10 hottest July days for the region were distributed randomly across the historical period, although global averages do show clustering in the past 2 decades. (Geophysical Research Letters, doi:10.1029/2010GL046582, 2011)

Self-shielding of thermal radiation by Chicxulub impact ejecta: Firestorm or fizzle?

As hypervelocity ejecta from the Chicxulub (Yucatan, Mexico) impact fell back to Earth, the surface may have received a deadly dose of thermal radiation sufficient to ignite global wildfires. Using a two-phase fluid flow code, which includes ejecta and air opacities in a radiative transfer calculation, we modeled the atmospheric reentry of spherules arriving at distal sites. The models predict a pulse of thermal radiation at the surface peaking at 5–15 kW/m 2 , analogous to an oven set on “broil” (~260° C). Previous calculations, which ignored spherule opacity, yielded >10 kW/m 2 sustained over >20 min and such an extended pulse is thought to be required for wood ignition. However, the new modeling suggests that fluxes only exceed the solar norm for ~30 min and are only >5 kW/m 2 for a few minutes. Previous models failed to consider the self-shielding effect of settling spherules, which block an increasing proportion of downward thermal radiation emitted by the later-arriving spherules. Such self-shielding may have prevented widespread wildfire ignition, although the thermal pulse may have been sufficient to ignite localized fires and kill fauna lacking temporary shelter. An opaque cap of submicron dust in the upper atmosphere could, however, override the self-shielding effect.

Comparison of fire patterns and fire frequency in two tropical savanna bioregions

Abstract Fire is a significant determinant of vegetation structure in Australia’s savannas and has been implicated in the decline of many species. Identifying the patterns of fire in the landscape is fundamental to understanding vegetation dynamics but variation over time and space makes generalization difficult and specific management recommendations elusive. In order to improve the knowledge base for fire management in tropical savannas, we investigated interregional variation in fire patterns in two Queensland bioregions, the Mount Isa Inlier (MII) and Cape York Peninsula (CYP), over a 5‐year period (1999–2003). Remotely sensed satellite data were used to identify burnt areas on a monthly basis for the western half of the CYP bioregion and about two‐thirds of the smaller MII. Fire scars were mapped from JPEG‐compressed, low‐resolution Landsat images using geographical information system technology and data were investigated to determine annual burning patterns. Patterns were interpreted with regard to meteorological information and recent fire history. The area burnt per annum on western CYP was generally an order of magnitude greater than the area burnt on the MII. In the biggest fire year, nearly 74% (5 295 098 ha) of the CYP landscape burnt, compared with 35% (1 770 771 ha) of the MII landscape. The minimum percentage of the CYP study area burnt in 1 year between 1999 and 2003 was 43.1%, compared with 1.6% for the MII. The reliability and amount of seasonal rainfall was a strong determinant of differences in time of fire occurrence and area burnt between regions. Widespread wildfires were significantly related to above average rainfall in the preceding 12 months in the Mt. Isa area but not in CYP. Rainfall also affected fire frequency. Predictable wet season rainfall on CYP allowed for a biennial fire return interval, while on the semiarid MII, the average fire return interval was 5 years or longer. We conclude that the fire patterns in the semiarid MII are similar to those reported for arid Australia, while fire patterns in western CYP are comparable with other mesic savanna areas.

Climate, Lightning, and Wildfire in the National Forests of the Southeastern United States: 1989-1998

We compiled the record of wildfires from each national forest unit in the southeastern United States for the period 1989 to 1998, then regressed annual fire numbers against lightning flash densities (as recorded by the National Lightning Detection Network) and measures of climatic drought (seasonal precipitation and Palmer Drought Severity Index [PDSI] values). Lightning-caused fires were most common in Florida, where seasonally-dry winters and high lightning-flash density elevate fire risk. Overall regression models consistently identified fire-season PDSI as the most influential explanatory variable in accounting for the spatial and temporal pattern of fires, whereas the contribution of lightning-flash density to regional patterns of wildfires is muted. Lightning density only enters the overall model when a single outlier forest unit from Florida is included in the regression analysis. With respect to physiographically defined regional regression models, lightning density was only a significant influence in the Coastal Plain-East, which included Florida. Some measure of climatic drought was uniformly present in all other regions, except in the driest portion of the study region, the Ozark-Ouachita Uplands. Elsewhere, geographic variation in effective moisture is highlighted. Drought for periods of up to 12 months is necessary to promote burning in the wetter forests of the Appalachian Highlands, but periods of antecedent drought necessary to trigger widespread wildfires are shorter in the warmer and drier Piedmont and Coastal Plain.

Reanalysis of tropospheric CO trends: Effects of the 1997–1998 wildfires

For the past decade NOAA/CMDL has measured tropospheric carbon monoxide from a global network of sampling sites. The resulting data set provides an internally consistent picture of CO in the lower troposphere that is used to study its distribution, trends and budget. All measurements were referenced to the so‐called CMDL Reference Scale (WMO 88), which was based on two sets of primary standards produced at CMDL during the late 1980s and early 1990s. A long‐term downward trend in tropospheric CO during the 1990s, overlaid with shorter periods of increase and decrease, was indicated from the air measurements. Primary standards prepared in 1999 and 2000 suggested that the scale had drifted upward over time, and that mixing ratios determined in field samples were underestimated. We have applied a time dependent correction to our CO measurements based upon four sets of primary standards. In this paper, we describe the revision of the CO scale and our atmospheric measurements. A reanalysis of tropospheric trends through 2001 was based on the revised global data set. The results support previous reports of a decline in tropospheric CO. This decrease is now found largely confined to the Northern Hemisphere, where dramatic reductions in fossil fuel emissions have reportedly occurred. In contrast, no significant trend is determined in the Southern Hemisphere between 1991 and 2001. Globally averaged CO exhibits large interannual variability, primarily reflecting year to year changes in emissions from biomass burning. Dramatic enhancements of tropospheric CO in 1997 and 1998 resulted from exceptionally widespread wildfires which provided a strong pulse of CO to the atmosphere. In years of extensive boreal biomass burning, fire emissions can perturb CO levels over regional and global scales, disturbing oxidation/reduction chemistry in the troposphere.

Microscopic charcoal in sediments: Quaternary fire history of the grassland and savanna regions in South Africa

AbstractThe microscopic charcoal content of several Quaternary pollen sequences is used to investigate fire history in South Africa both during the Holocene and the Late Pleistocene. Although fluctuations in charcoal composition are recorded, it is difficult to link them directly to either human‐made or natural fires. Strong long‐term variations in microscopic charcoal of Middle and Upper Pleistocene layers are independent of pollen indications of past temperature and moisture conditions. Holocene charcoal sequences from different areas show no correlation, so no phases of regional burning are found. Some fluctuations in charcoal probably are the result of local burning in the various regions. The arrival of Iron Age people some 2000 yr ago apparently did not coincide with widespread wild fires, as these events do not consistently appear in regional microscopic charcoal records. The only exception appears to be the Wonderkrater spring deposit. Relatively open savanna environments, which are implied by pollen analysis at some sites during this period and the generally low microscopic charcoal contents, were either caused by climate change or controlled burning by Iron Age people. Copyright © 2002 John Wiley & Sons, Ltd.

Climate Assessment for 2000

The global climate in 2000 was again influenced by the long-running Pacific cold episode (La Niña) that began in mid-1998. Consistent with past cold episodes, enhanced convection occurred across the climatologically convective regions of Indonesia and the western equatorial Pacific, while convection was suppressed in the central Pacific. The La Niña was also associated with a well-defined African easterly jet located north of its climatological mean position and low vertical wind shear in the tropical Atlantic and Caribbean, both of which contributed to an active North Atlantic hurricane season. Precipitation patterns influenced by typical La Niña conditions included 1) above-average rainfall in southeastern Africa, 2) unusually heavy rainfall in northern and central regions of Australia, 3) enhanced precipitation in the tropical Indian Ocean and western tropical Pacific, 4) little rainfall in the central tropical Pacific, 5) below-normal precipitation over equatorial east Africa, and 6) drier-than-normal conditions along the Gulf coast of the United States. Although no hurricanes made landfall in the United States in 2000, another active North Atlantic hurricane season featured 14 named storms, 8 of which became hurricanes, with 3 growing to major hurricane strength. All of the named storms over the North Atlantic formed during the August–October period with the first hurricane of the season, Hurricane Alberto, notable as the third-longest-lived tropical system since reliable records began in 1945. The primary human loss during the 2000 season occurred in Central America, where Hurricane Gordon killed 19 in Guatemala, and Hurricane Keith killed 19 in Belize and caused $200 million dollars of damage. Other regional events included 1) record warm January–October temperatures followed by record cold November–December temperatures in the United States, 2) extreme drought and widespread wildfires in the southern and western Unites States, 3) continued long-term drought in the Hawaiian Islands throughout the year with record 24-h rainfall totals in November, 4) deadly storms and flooding in western Europe in October, 5) a summer heat wave and drought in southern Europe, 6) monsoon flooding in parts of Southeast Asia and India, 7) extreme winter conditions in Mongolia, 8) extreme long-term drought in the Middle East and Southwest Asia, and 9) severe flooding in southern Africa. Global mean temperatures remained much above average in 2000. The average land and ocean temperature was 0.39°C above the 1880–1999 long-term mean, continuing a trend to warmer-than-average temperatures that made the 1990s the warmest decade on record. While the persistence of La Niña conditions in 2000 was associated with somewhat cooler temperatures in the Tropics, temperatures in the extratropics remained near record levels. Land surface temperatures in the high latitudes of the Northern Hemisphere were notably warmer than normal, with annually averaged anomalies greater than 2°C in parts of Alaska, Canada, Asia, and northern Europe.

Inter‐hemispheric synchrony of forest fires and the El Niño‐Southern Oscillation

AbstractFire histories were compared between the south‐western United States and northern Patagonia, Argentina using both documentary records (1914–87 and 1938–96, respectively) and tree‐ring reconstructions over the past several centuries. The two regions share similar fire–climate relationships and similar relationships of climatic anomalies to the El Niño–Southern Oscillation (ENSO). In both regions, El Niño events coincide with above‐average cool season precipitation and increased moisture availability to plants during the growing season. Conversely, La Niña events correspond with drought conditions. Monthly patterns of ENSO indicators (southern oscillation indices and tropical Pacific sea surface temperatures) preceding years of exceptionally widespread fires are highly similar in both regions during the 20th century. Major fire years tend to follow the switching from El Niño to La Niña conditions. El Niño conditions enhance the production of fine fuels, which when desiccated by La Niña conditions create conditions for widespread wildfires. Decadal‐scale patterns of fire occurrence since the mid‐17th century are highly similar in both regions. A period of decreased fire occurrence in both regions from c. 1780–1830 coincides with decreased amplitude and/or frequency of ENSO events. The interhemispheric synchrony of fire regimes in these two distant regions is tentatively interpreted to be a response to decadal‐scale changes in ENSO activity. The ENSO–fire relationships of the south‐western USA and northern Patagonia document the importance of high‐frequency climatic variation to fire hazard. Thus, in addition to long‐term trends in mean climatic conditions, multi‐decadal scale changes in year‐to‐year variability need to be considered in assessments of the potential influence of climatic change on fire regimes.