A central challenge in global change research is the projection of the future behavior of a system based upon past observations. Tree-ring data have been used increasingly over the last decade to project tree growth and forest ecosystem vulnerability under future climate conditions. But how can the response of tree growth to past climate variation predict the future, when the future does not look like the past? Space-for-time substitution (SFTS) is one way to overcome the problem of extrapolation: the response at a given location in a warmer future is assumed to follow the response at a warmer location today. Here we evaluated an SFTS approach to projecting future growth of Douglas-fir (Pseudotsuga menziesii), a species that occupies an exceptionally large environmental | 5147 KLESSE Et aL.

[1] Thirty one hydrological time series of shallow groundwater levels, precipitation, and moisture-sensitive tree ring chronologies were analyzed and related to two climate indices: Niño 3.4 and PDO. Spearman rank correlation and spectral analyses (multitaper method, continuous wavelet transform, and wavelet coherence) were used to document the influence of El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) on shallow (depth < 20 m) groundwater level records from the Canadian Prairies. Modes of variability in the 2-7, 7-10, and 18-22 year bands were detected and reconstructed. Correlations and wavelet coherence between these oscillation modes and the climate indices suggest that variability in the 2-7 and 7-10 year bands is highly influenced by ENSO. The oscillation modes in the 18-22 year band reflect a negative correlation with the PDO index. When either of these teleconnections (ENSO/PDO) is in their respective positive phases, groundwater levels reflect the effect of associated warmer and drier winters experienced over much of interior Canada and the US, affecting important resource inputs to the hydrological cycle and groundwater recharge.

No abstract

ABSTRACT:The Canadian Prairies have experienced severe and extended droughts that have had significant impacts on agriculture, energy and other socio-economic sectors; it is therefore desirable to assess future changes to drought characteristics in this drought prone region, in the context of a changing climate. This study addresses validation and projected changes to short-and long-term drought characteristics, i.e. severity, frequency and duration, over the Canadian Prairies, using an ensemble of ten Canadian RCM (CRCM) simulations, of which five correspond to the current 1971-2000 period and the other five are the matching simulations for the future 2041-2070 period. These five pairs of current and future CRCM simulations were driven by five different members of a Canadian Global Climate Model ensemble. Validation of CRCM simulated precipitation suggests that the model reproduces the observed precipitation distribution for all seasons, except summer, across a large portion of the Canadian Prairies. However, comparison of CRCM simulated drought characteristics with those observed suggests that the model has difficulties in reproducing observed severity, frequency and duration of drought events, particularly those associated with longer events, possibly due to the overestimation of summer precipitation by the model. Analysis of projected changes to precipitation and drought characteristics between the 1971-2000 and 2041-2070 periods suggests a decrease in mean precipitation in summer and an increase for the other seasons, while the severity, frequency and maximum duration of both short-and long-term droughts are projected to increase over the southern Prairies, with the largest projected changes associated with longer drought events. Classification of the watersheds spanning the southern Prairies based on changes to both severity and frequency further reveal the vulnerability of this region in a changing climate.

Annual area burned (AAB) variability in northwestern North America was inferred from 38 tree-ring width chronologies widely distributed across boreal regions and spanning the past 300 years and the minimum 1833—1998 interval. AAB estimates accounted for up to 61% of the variance in AAB observed from 1959 to 1998, and were verified using a split sample calibration-verification scheme. Spatial correlation maps of gridded temperature and precipitation data provided an indication of the reliability of the reconstruction to approximate fire-conducive climate variability beyond the period of calibration. Singular spectrum analysis and analysis of variance suggested that AAB has significantly changed during the course of the past 150 years toward increasing variance. Recent 1959—1998 decadal changes in AAB of northwestern North America fitted well within an oscillatory mode centred on 26.7 years and accounting for 21.1% of the variance in the reconstruction. As in previous studies, the current findings suggest that AAB is correlated to seasonal land/ocean temperature variability and that future warming could lead to greater AAB. However, the study has the weakness of not accounting for complex interactions between climate and ecosystem processes and thus its results should be interpreted with caution. We suggest that a calibration model conducted on multiple types of fire proxies (tree rings, charcoal data, fire scars and stand-establishment records) could be relevant for addressing these weaknesses.