Abstract. Drought is a recurring extreme climate event and among the most
costly natural disasters in the world. This is particularly true over Canada,
where drought is both a frequent and damaging phenomenon with impacts on
regional water resources, agriculture, industry, aquatic ecosystems, and
health. However, nationwide drought assessments are currently lacking and
impacted by limited ground-based observations. This study provides a
comprehensive analysis of historical droughts over the whole of Canada,
including the role of large-scale teleconnections. Drought events are
characterized by the Standardized Precipitation Evapotranspiration Index
(SPEI) over various temporal scales (1, 3, 6, and 12 consecutive months,
6 months from April to September, and 12 months from October to September)
applied to different gridded monthly data sets for the period 1950–2013.
The Mann–Kendall test, rotated empirical orthogonal function, continuous
wavelet transform, and wavelet coherence analyses are used, respectively, to
investigate the trend, spatio-temporal patterns, periodicity, and
teleconnectivity of drought events. Results indicate that southern (northern)
parts of the country experienced significant trends towards drier (wetter)
conditions although substantial variability exists. Two spatially
well-defined regions with different temporal evolution of droughts were
identified – the Canadian Prairies and northern central Canada. The analyses
also revealed the presence of a dominant periodicity of between 8 and 32 months in the Prairie region and between 8 and 40 months in the northern central
region. These cycles of low-frequency variability are found to be associated
principally with the Pacific–North American (PNA) and Multivariate El
Niño/Southern Oscillation Index (MEI) relative to other considered
large-scale climate indices. This study is the first of its kind to identify
dominant periodicities in drought variability over the whole of Canada in
terms of when the drought events occur, their duration, and how often they occur.