Search

The relations between groundwater level fluctuations and past climatic variations are explored using available data from the provincial observation well network, climate data and hydrometric data from the two major hydro-climatic zones of British Columbia. The majority of these well records start in the late 1970s or 1980s, providing only 20 to 30 years of record at most, and only a few of these wells monitor aquifers in “pristine” areas that reflect natural variability; the others have been influenced by human activity. Mean monthly groundwater levels were used to manually classify the wells into rainfall- and snowmelt-dominated seasonal cycles. Temporal trends of groundwater levels and a simple recharge measure were calculated using the non-parametric Spearman’s rank correlation coefficient over a common period from 1976–1999. This period was selected to coincide with the positive phase of the Pacific Decadal Oscillation (PDO) so as to eliminate the potential impact a shift in the PDO might have on groundwater levels and recharge trends. Overall, late summer groundwater levels appear to have lowered across the province. Trends in recharge were more variable with both positive and negative trends. However, most of the trend results were non-significant. This assessment was complicated by the varied nature of the climate in different parts of the province, which determines the hydrologic regime (pluvial, nival, glacierized, mixed), the complexity of the groundwater system as it relates to the connection between groundwater and surface water, and the remote sources of many rivers in the mountainous regions of the province. Les relations entre les fluctuations des niveaux des eaux souterraine et les variations climatiques passées sont explorées à l’aide des données disponibles provenant du réseau piézométrique provincial, des données climatiques et des données hydrométriques des deux principales zones hydroclimatiques de la Colombie-Britannique. Ces registres de puits ont été lancés pour la plupart vers la fin des années 1970 ou dans les années 1980, ce qui nous donne seulement entre 20 et 30 années d’enregistrements tout au plus, et seuls quelques-uns de ces puits permettent de surveiller les aquifères dans des zones « vierges » qui reflètent la variabilité naturelle; les autres ayant subi l’influence de l’activité humaine. Les niveaux mensuels moyens des eaux souterraines ont été utilisés pour classer manuellement les puits en cycles saisonniers dominés par les précipitations et la fonte des neiges. Les tendances temporelles des niveaux des eaux souterraines et une simple mesure de l’alimentation en eau souterraine ont été calculées à l’aide du coefficient de corrélation de rang de Spearman non paramétrique sur une période commune allant de 1976 à 1999. Cette période a été sélectionnée afin qu’elle coïncide avec la phase positive de l’oscillation décennale du Pacifique (ODP) de façon à éliminer l’incidence éventuelle qu’un changement dans l’ODP pourrait avoir sur les niveaux des eaux souterraines et sur les tendances en matière d’alimentation. Dans l’ensemble, les niveaux des eaux souterraines vers la fin de l’été semblent avoir diminué partout dans la province. Les tendances en matière d’alimentation de la nappe souterraine étaient plus variables, celles-ci pouvant être tant positives que négatives. Cependant, la plupart des résultats liés aux tendances étaient non significatifs. Cette évaluation a été compliquée par des facteurs comme la nature variée du climat dans différentes parties de la province, lequel détermine le régime hydrologique (pluvial, nival, englacé, mixte), la complexité du système aquifère en ce qu’il se rapporte à la relation entre les eaux souterraines et les eaux de surface, et les sources éloignées de nombreuses rivières dans les régions montagneuses de la province. [ABSTRACT FROM AUTHOR]

The hydrology of ecosystem succession gives rise to new challenges for the analysis and modelling of water balance components. Recent large-scale alterations of forest cover across the globe suggest that a significant portion of new biophysical environments will influence the longterm dynamics and limits of water fluxes compared to presuccession conditions. This study assesses the estimation of summer evapotranspiration along three FLUXNET sites at Campbell River, British Columbia, Canada using a data-driven soil water balance model validated by Eddy Covariance measurements. It explores the sensitivity of the model to different forest succession states, a wide range of computational time steps, rooting depths, and canopy interception capacity values. Uncertainty in the measured EC fluxes resulting in an energy imbalance was consistent with previous studies and does not affect the validation of the model. The agreement between observations and model estimates proves that the usefulness of the method to predict summer AET over mid- and long-term periods is independent of stand age. However, an optimal combination of the parameters rooting depth, time step and interception capacity threshold is needed to avoid an underestimation of AET as seen in past studies. The study suggests that summer AET could be estimated and monitored in many more places than those equipped with Eddy Covariance or sap-flow measurements to advance the understanding of water balance changes in different successional ecosystems. [ABSTRACT FROM AUTHOR]

A recent epidemic of mountain pine beetles (MPB) has caused mortality in extensive stands of pine trees in British Columbia, Canada. The epidemic has been attributed, in part, to the recent warming trend in winter in western Canada, as MPB experience mortality during extreme cold spells. This study aimed to clarify the roles of synoptic-scale circulation and large-scale climate modes in these recent trends. Potential cold-mortality events were identified by comparing recorded daily minimum air temperatures with experimentally determined critical thresholds. Annual event frequency has declined over past decades, and between 1998 and 2001 temperatures did not reach the 100% MPB mortality thresholds at the stations analysed. Event frequencies depended on the phase of the teleconnection indices. In particular, after the shift to a predominantly positive phase of the Pacific Decadal Oscillation (PDO) following 1976, cold-mortality events occurred mainly during strongly negative Arctic Oscillation (AO) years. The dominant synoptic-scale circulation pattern causing widespread low temperatures is Arctic Outbreak, although other circulation types can be important, depending on location. The frequencies of these cold circulation types varied with the teleconnection indices. In addition, the conditional probability of temperatures cold enough to cause MPB mortality for a given synoptic type varies with the teleconnection phase, particularly for the Pacific North America circulation pattern and PDO. [ABSTRACT FROM AUTHOR]