INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 22: 1617–1644 (2002) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.813 RECENT VARIATIONS IN SEASONALITY OF TEMPERATURE AND PRECIPITATION IN CANADA, 1976–95 PAUL H. WHITFIELD, a, * KARIN BODTKER b and ALEX J. CANNON a a Meteorological Service of Canada, Environment Canada, 700–1200 West 73rd Avenue, Vancouver, B.C. V6P 6H9, Canada b School of Resource and Environmental Management, Simon Fraser University, Vancouver, B.C., Canada Received 2 November 2001 Revised 20 May 2002 Accepted 23 May 2002 ABSTRACT A previously reported analysis of rehabilitated monthly temperature and precipitation time series for several hundred stations across Canada showed generally spatially coherent patterns of variation between two decades (1976–85 and 1986–95). The present work expands that analysis to finer time scales and a greater number of stations. We demonstrate how the finer temporal resolution, at 5 day or 11 day intervals, increases the separation between clusters of recent variations in seasonal patterns of temperature and precipitation. We also expand the analysis by increasing the number of stations from only rehabilitated monthly data sets to rehabilitated daily sets, then to approximately 1500 daily observation stations. This increases the spatial density of data and allows a finer spatial resolution of patterns between the two decades. We also examine the success of clustering partial records, i.e. sites where the data record is incomplete. The intent of this study was to be consistent with previous work and explore how greater temporal and spatial detail in the climate data affects the resolution of patterns of recent climate variations. The variations we report for temperature and precipitation are taking place at different temporal and spatial scales. Further, the spatial patterns are much broader than local climate regions and ecozones, indicating that the differences observed may be the result of variations in atmospheric circulation. Copyright  2002 Environment Canada. Published by John Wiley & Sons, Ltd. KEY WORDS: k-means clustering; spatial patterns; cohesion; time steps; temperature; precipitation 1. INTRODUCTION Canadian climate varies over time and space. Some areas become warmer or wetter, while others grow cooler or drier. Recent work to analyse trends in temperature and precipitation data during the 20th century has found coherent signals in both annual and seasonal data sets. Vega et al. (1998) described interdecadal climate variations across the USA, and others have examined variations in temperature and precipitation in different regions of the world over recent decades (e.g. Coughlan, 1979; Jones and Conway, 1997; Conway 1998; Lee et al., 2000; Osborn et al., 2000; Zhang et al., 2000). Bonsal et al. (1999) reported interdecadal variability in precipitation on the Canadian Prairies, including a shift in maximum precipitation from June to July. In a similar study of temperature, Bonsal et al. (2001) found that mean annual temperature in southern Canada has increased by an average of 0.9 ° C, with the largest increases in spring and fall. A trend towards earlier spring flowering in Alberta was found to be related to the incidence of El Ni˜ no events and to increases in Pacific sea-surface temperatures (Beaubien and Freeland, 2000). The effect that climate variations have on our environment, society, and economy is a topic that currently generates great interest. Understanding how climate affects natural processes, especially with regard to resources upon which we are dependent, has become increasingly important (e.g. Filon, 2000). * Correspondence to: Paul H. Whitfield, Meteorological Service of Canada, Environment Canada, 700–1200 West 73rd Avenue, Vancouver, BC V6P 6H9, Canada; e-mail: paul.whitfield@ec.gc.ca Copyright  2002 Environment Canada. Published by John Wiley & Sons, Ltd.