No abstract

No abstract

Abstract:Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy-covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration (E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB-06, an 85-year-old almost pure stand of pine trees, was first attacked in 2006, and by 2010,~80% of the trees had been killed. MPB-03, a 110-year-old stand with an overstory consisting of over 90% pine and a developed sub-canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB-06 and in March 2007 at MPB-03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB-06, and from 280 to 297 mm at MPB-03, showing relatively little year-to-year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley-Taylor (a), and the canopy-atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s À1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit-dependent a obtained at high soil water content. Calculated water deficits indicated some water-supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation.

Abstract. Thermal and surface offsets describe mean annual ground temperature relative to mean annual air temperature, and for permafrost modelling they are often predicted as a function of surface characteristics and topography. As macroclimatic conditions influence the effectiveness of the underlying processes, knowledge of surface- and topography-specific offsets is not easily transferable between regions, limiting the applicability of empirical permafrost distribution models over areas with strong macroclimatic gradients. In this paper we describe surface and thermal offsets derived from distributed measurements at seven field sites in British Columbia. Key findings are (i) a surprisingly small variation of the surface offsets between different surface types; (ii) small thermal offsets at all sites (excluding wetlands and peat); (iii) a clear influence of the micro-topography at wind exposed sites (snow-cover erosion); (iv) a north–south difference of the surface offset of 4 °C in vertical bedrock and of 1.5–3 °C on open (no canopy) gentle slopes; (v) only small macroclimatic differences possibly caused by the inverse influence of snow cover and annual air temperature amplitude. These findings suggest that topoclimatic factors strongly influence the mountain permafrost distribution in British Columbia.

Water resources from the Columbia River Basin are intensely used for domestic, agricultural, industrial, and hydroelectric generation needs. Water availability in the Pacific Northwest is influenced by several ocean-atmosphere modes of climate variability that occur in the Pacific Ocean. Climate change has the potential to alter these relationships and influence both the volume and timing of streamflow in the snowmelt-dominated tributaries to the Columbia River. Here, the historical influence of climate variability and recent climate warming on the volume and timing of streamflow for 40 tributary streams in the Columbia River Basin of Canada were evaluated. Regional relationships were found between streamflow and several Pacific Ocean Climate Indices, including the already established relationships with the Pacific Decadal Oscillation (PDO) and El Nino/Southern Oscillation (ENSO). However, in recent decades the statistical relationship between streamflow and climate indices has become weaker, which has implications for managers using these indices as decision-making tools. A comparison of the average annual streamflow for the cool PDO phase, which occurred from 1947-1976, to the more recent cool phase from 1999-2011 indicated a 11% decline across the Canadian portion of the basin. Removing the influence of these climate indices on historical streamflow revealed decreases in the residual streamflow beginning sometime in the 1980's. The potential role of increased temperatures on streamflow was investigated and statistically significant relationships between decreased streamflow and increased temperatures in the summer months were found, particularly to the number of days over 18°C. The results suggest that climate change may be altering the historical relationship between climate indices and streamflow in the Canadian portion of the Columbia Basin.