Trends and periodicities in the Canadian Drought Code and their relationships with atmospheric circulation for the southern Canadian boreal forest (original) (raw)
Related papers
2006
Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstruction of the mean July-August temperature were developed using a network of 120 well-replicated tree-ring chronologies covering the area of the eastern Boreal Plains to the eastern Boreal Shield of Canada. The reconstructions were performed using 54 time-varying reconstruction submodels that explained up to 50% of the regional drought variance during the period of 1919-84. Spatial correlation fields on the six reconstructions revealed that the meridional component of the climate system from central to eastern Canada increased since the mid-nineteenth century. The most obvious change was observed in the decadal scale of variability. Using 500-hPa geopotential height and wind composites, this zonal to meridional transition was interpreted as a response to an amplification of long waves flowing over the eastern North Pacific into boreal Canada, from approximately 1851 to 1940. Composites with NOAA Extended Reconstructed SSTs indicated a coupling between the meridional component and tropical and North Pacific SST for a period covering at least the past 150 yr, supporting previous findings of a summertime global ocean-atmosphereland surface coupling. This change in the global atmospheric circulation could be a key element toward understanding the observed temporal changes in the Canadian boreal forest fire regimes over the past 150 yr.
Journal of Climate, 2006
Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstruction of the mean July-August temperature were developed using a network of 120 well-replicated tree-ring chronologies covering the area of the eastern Boreal Plains to the eastern Boreal Shield of Canada. The reconstructions were performed using 54 time-varying reconstruction submodels that explained up to 50% of the regional drought variance during the period of 1919-84. Spatial correlation fields on the six reconstructions revealed that the meridional component of the climate system from central to eastern Canada increased since the mid-nineteenth century. The most obvious change was observed in the decadal scale of variability. Using 500-hPa geopotential height and wind composites, this zonal to meridional transition was interpreted as a response to an amplification of long waves flowing over the eastern North Pacific into boreal Canada, from approximately 1851 to 1940. Composites with NOAA Extended Reconstructed SSTs indicated a coupling between the meridional component and tropical and North Pacific SST for a period covering at least the past 150 yr, supporting previous findings of a summertime global ocean-atmosphereland surface coupling. This change in the global atmospheric circulation could be a key element toward understanding the observed temporal changes in the Canadian boreal forest fire regimes over the past 150 yr.
Atmospheric and oceanic variability related to dry regimes in Canada
This study documents and assesses the atmospheric and oceanic variability associated with growing season (May to August) droughts over the Canadian Prairies. For comparison, extreme wet seasons or pluvials are also examined. Using the Palmer Z-Index as a drought indicator, extreme dry and wet seasons are firstly identified for the period 1950 to 2007. Inter-relationships among several atmospheric parameters including large to synoptic-scale circulation patterns, low-level moisture transport, moisture convergence, precipitable water content, and cyclone frequency are then assessed during extreme drought and pluvial periods. In addition, links to the previous winter's global sea-surface temperature (SST) patterns are identified using the multivariate technique of singular value decomposition. These circulation patterns over western North America and their associated moisture transport anomalies into the Prairies show some linkages to previous winter SST patterns both globally, and...
Atmosphere-Ocean
We identify Dry and Wet months for the Canadian Prairies during the 40-year period 1946-1985 and investigate their relationship to the Northern Hemisphere circulation at the 50-and 100-kPa levels. The target area is first subdivided into five zones on the basis of characteristic differences in precipitation climatology, and for each zone the dates of occurrence of dry and wet months are determined. These events are then stratified into five "seasons". Much of the analysis focuses on the two growing seasons: Spring, defined as April and May, and Early Summer, June and July. Composite anomaly fields for the Northern Hemisphere are constructed for the 50-kPa level by "season" and zone, and for the Dry and Wet groupings. For each zone, the two 50-kPa anomaly fields Dry and Wet are clearly distinguishable, not only over North America but in many instances, upstream and downstream of the continent. Composite anomalies are shown to be zone-sensitive. The 100-and 50-kPa anomalous wind fields associated with the Dry and Wet regimes, respectively, are found to be consistent with dynamic and thermodynamic processes that control the production of precipitation. Anomaly field structures over the oceans and North America are related to Northern Hemisphere tropospheric circulation modes, including the PNA, NPO and NAO. High-latitude blocking over the North Atlantic and North Pacific is often associated with Wet months, particularly in Spring, whereas "in situ" blocking over western Canada or simply amplified ridging extending northward from the western United States is almost invariably associated with the Dry months. RÉSUMÉ Après avoir identifié les mois humides et secs pour lapériode de 1946 à 1985, dans les Prairies canadiennes, on étudie la relation avec la circulation hémisphérique septentrio
Canadian Water Resources Journal, 2006
Forest fires in Canada are directly influenced by the state of the climate system. The strong connection between climate and fire, along with the dynamic nature of the climate system, causes the extent, severity and frequency of fires to change over time. For instance, many reconstructions of the history of forest fires across boreal Canada report a general decrease in fire activity since ~1850 which could, in part, result from changes in climate. This paper describes progress in characterizing the variability in fire-conducive droughts in the central and eastern Canadian boreal forests during the past three centuries. An extensive network of drought-sensitive tree-ring records from Manitoba, Ontario and Quebec was used to develop five multi-century reconstructions of the mean July Canadian Drought Code and one reconstruction of mean July and August temperatures. Correlation analyses with regional fire statistics (common period 1959−1998) showed that drought estimates are accurate enough to approximate fire activity and, hence, the estimates are relevant for the study of climate change impacts on Canadian forests. Spatial correlation analysis over the period 1768−1998 revealed that variability between the west and east has increased since the mid−19th century, specifically the decade-to-decade variability and the frequency of extreme events. Based on the synoptic characteristics of recent droughts, we interpret this change in variability as a response to an increasing frequency of upper level ridging and troughing over western and eastern Canada, respectively. The increasing horizontal movement of humid air masses over eastern Canada since ~1850 could have contributed to the creation of moister conditions that are less suitable for fire.
Canadian Journal of Forest Research, 2005
This paper investigates the influence of surface climate and atmospheric circulation on radial growth of eight boreal tree species growing in the Duck Mountain Provincial Forest, Manitoba, Canada. Tree-ring residual chronologies were built, transformed into principal components (PCs), and analysed through correlation and response functions to reveal their associations to climate (temperature, precipitation, and drought data for the period 1912-1999, as well as local geopotential height data for the period 1948-1999). Geopotential height correlation and composite charts for the Northern Hemisphere were also constructed. Correlation and response function coefficients indicated that radial growth of all species was negatively affected by temperature-induced drought stresses from the summers previous and current to ring formation. The summer drought stress alone explained nearly 28% of the variance in PC1. Warm spring temperature was also a positive factor for Pinus banksiana Lamb. and Picea glauca (Moench) Voss, but a negative one for all hardwoods. Analyses performed on geopotential height highlighted the importance of the Northern Hemispheric atmospheric circulation in the species' response to climate. The variability within the 500-hPa level over southern Manitoba explained 39% and 58% of the variability in PC1 and PC2, respectively. The relationships were highly significant with the middle and high troposphere during spring and late summer (determinant factor for growing season length) and with the troposphere and stratosphere during summer. The sensitivity of tree growth to atmospheric circulation exceeded the synoptic scale, with a response associated with yearly variations in the amplitude of the mid-tropospheric longwaves.
Atmosphere-Ocean, 2010
We assessed the impacts of some key Pacific ocean-atmosphere circulation patterns on annual cycles of temperature and precipitation across British Columbia, Yukon, and southeast Alaska. The El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and ENSO conditional on PDO states were considered in composite analyses of 71 long, high-quality datasets from surface meteorological stations. Month-bymonth, station-by-station Monte Carlo bootstrap tests were employed to assess statistical significance. The results trace precipitation and temperature responses as a function of location, season, and climate mode. In summary, temperature responses were relatively uniform, with higher (lower) temperatures during the warm (cool) phases of these circulation patterns. Nevertheless, strength and seasonal persistence varied considerably with location and climate mode. Impacts were generally most consistent in winter and spring but could extend through most of the year. Overall spatiotemporal patterns in precipitation response were decoupled from those in temperature and were far more heterogeneous. Complexities in precipitation signals included north-south inverse teleconnectivity along the Pacific coast, with a zero-response hinge point in the approximate vicinity of northern Vancouver Island; seasonally opposite anomalies in several interior regions, which might conceivably reflect contrasting effects of Pacific climate modes on wintertime frontal storms versus summertime convective storms; and a consistent lack of substantial response in northwestern British Columbia and possibly southwestern Yukon, conjectured to reflect complications associated with the Icefield Ranges. The product is intended primarily as a basic-level set of climate response maps for hydrologists, biologists, foresters, and others who require empirical assessments of relatively local-scale, year-round ENSO and PDO effects across this broad region. réSuMé [Traduit par la rédaction] Nous avons évalué les répercussions de certaines configurations de circulation océan Pacifique-atmosphère clés sur les cycles annuels de température et de précipitations en Colombie-Britannique, au Yukon et dans le sud-est de l'Alaska. Nous avons examiné l'El Niño-oscillation australe (ENSO), l'Oscillation décennale du Pacifique (ODP) et la sensibilité de l'ENSO à l'égard des états de l'ODP dans des analyses composites de 71 ensembles de données longs et de bonne qualité de stations météorologiques de surface. Nous avons employé des tests d'amorçage de Monte Carlo mois par mois, station par station, pour mesurer la signification statistique. Les résultats tracent les réponses des précipitations et de la température en fonction de l'endroit, de la saison et du mode climatique. En résumé, les réponses de la température étaient relativement uniformes, avec les températures les plus élevées (basses) durant les phases chaudes (froides) de ces configurations de circulation. Néanmoins, la force et la persistance saisonnière variaient considérablement selon l'endroit et le mode climatique. Les répercussions étaient généralement plus cohérentes en hiver et au printemps mais pouvaient se faire sentir durant la majeure partie de l'année. Généralement, les configurations spatiotemporelles générales dans la réponse des précipitations étaient dissociées de celles de la température et étaient beaucoup plus hétérogènes. Les complexités dans les signaux de précipitations comprenaient une téléconnexion nord-sud inverse le long de la côte du Pacifique, avec un point charnière de réponse nulle dans le voisinage approximatif du nord de l'île de Vancouver; des anomalies saisonnièrement opposées dans plusieurs régions intérieures, qui pourraient refléter des effets contrastants de modes climatiques du Pacifique sur les tempêtes frontales hivernales par rapport aux tempêtes convectives estivales; et un manque constant de réponse marquée dans le nord-ouest de la Colombie-Britannique et possiblement le sud-ouest du Yukon, que l'on croit attribuables aux complications liées aux chaînons des Glaciers. Le produit est principalement destiné à servir d'ensemble de base de cartes de réponse climatique pour les hydrologistes, les biologistes, les forestiers, etc. qui ont besoin d'évaluations empiriques des effets de l'ENSO et de l'ODP à une échelle assez locale, toute l'année, dans cette grande région.
Canadian Precipitation Patterns Associated with the Southern Oscillation
Journal of Climate, 1997
Precipitation responses over Canada associated with the two extreme phases of the Southern Oscillation (SO), namely El Niño and La Niña, are identified. Using the best available precipitation data from 1911 to 1994, both the spatial and temporal behavior of the responses are analyzed from the El Niño/La Niña onset to several seasons afterward. Composite and correlation analyses indicate that precipitation over a large region of southern Canada extending from British Columbia, through the prairies, and into the Great Lakes region is significantly influenced by the SO phenomenon. The results show a distinct pattern of negative (positive) precipitation anomalies in this region during the first winter following the onset of El Niño (La Niña) events. During this same period, significant positive precipitation anomalies occur over the northern prairies and southeastern Northwest Territories in association with El Niño events. Statistical significance of the responses is tested by the Student's t-test and the Wilcoxon rank-sum test, while field significance is established through the Monte Carlo procedure. All of the significant precipitation anomalies can be explained by the associated upper-atmospheric flow patterns, which during the first winter following the onset of El Niño (La Niña) events resemble the positive (negative) phase of the Pacific-North American (PNA) pattern. Significant correlations between Southern Oscillation index (SOI) values and the observed precipitation anomalies over southern Canada suggest the possibility of developing a long-range forecasting technique for Canadian precipitation based on the occurrence and evolution of the various phases of the SO.