Climatic variability and change can have profound impacts on the hydrologic regime of a watershed, especially in regions that are sensitive to changes in climate, such as the northern latitudes and alpine-fed regions of western Canada. Quantifying historical spatial and temporal changes in hydrological data can provide useful information as to how water resources are affected by climatic and atmospheric forcings, as well as create an understanding of potential future variability. Trends in western Canadian runoff are examined for the period of 1976–2010. Regional patterns of spatial variability are quantified using a principal component analysis (PCA) that results in the identification of three hydrological regions. Both watershed-scale and PCA trend results show increased runoff in the northern-most watersheds, while decreased water availability has generally affected the mid-latitude basins. The southern watersheds show increases and decreases in runoff with no significant trends. Runoff is shown to be positively correlated with precipitation. Runoff in some regions of western Canada is shown to be influenced by the Pacific Decadal Oscillation and Pacific North American (PNA) modes of atmospheric variability. The results of this analysis provide water managers with an indication of the direction and magnitude of changing water availability in western Canada.