Spatiotemporal dynamics of historical droughts over Canada: role of observational uncertainties and teleconnections

Drought is a naturally occurring environmental phenomenon, and a major costly natural hazard that can have devastating impacts on regional water resources, agriculture, energy and other social-ecological systems. Of particular interest here is drought occurrence over Canada, where drought is both a frequent and damaging phenomenon, particularly in the interior Prairie region. However, nation-wide drought assessments are currently lacking and hampered partly by observational uncertainties. Therefore, this study aims to fill these gaps by providing a comprehensive analysis of historical droughts over the whole of Canada, including the role of observational uncertainties and teleconnectivity. This is carried out by analysing different monthly precipitation and temperature products for the period 1950 - 2013. Drought events are characterized by the Standardized Precipitation-Evapotranspiration Index (SPEI) over various temporal scales (1, 3, 6, and 12 consecutive months and 6 months from April to September and 12 months from October to September). First, trends in the SPEI are investigated by means of the Modified Mann Kendall test, while the Pettitt test was used to detect change points/transition years during the period of record. Major spatial patterns of long-term change, inter/intra-annual variability and periodicity of drought events are then characterized using the Rotated Empirical Orthogonal Function, and Continuous Wavelet Transform techniques. In addition, potential key drivers of drought are investigated using Wavelet Coherence Analysis, with a special emphasis on the role played by large-scale modes of climate variability. This provides important insight into the physical and dynamical mechanisms associated with the variability of drought events over different Canadian sub-regions.