Characterizing the spatial and temporal variability of June–July moisture conditions in the Canadian prairies

Abstract

AbstractPalmer's moisture anomaly index (Z‐index) was used to characterize the frequency, severity, and spatial extent of June–July moisture anomalies for 43 crop districts across the Canadian prairies during 1920–99. In addition, the main modes of spatial and temporal variability in moisture conditions were identified and used to elucidate the physical mechanisms responsible for causing these moisture anomalies to occur. The crop districts were divided into five relatively homogeneous moisture regions using cluster analysis, and moisture anomaly statistics were analysed for each region.The single most severe June–July drought on the Canadian prairies occurred in 1961. This drought covered more than 86% of the study region and had a mean severity (Z‐index) of −5.67. Other severe June–July droughts occurred in the Canadian prairies (in order of severity) in 1988, 1936, 1929, and 1937. The results demonstrated that the severity and spatial extent of moisture anomalies on the Canadian prairies are strongly correlated, indicating that the more severe events tend to affect larger areas. The most drought‐prone regions experienced moisture conditions detrimental to crop production in approximately one year out of every six years.The spatial analysis revealed the existence of three preferred spatial patterns of moisture variability on the Canadian prairies and each pattern can be attributed to a unique set of atmospheric and oceanic forcings. The temporal analysis verified the presence of coherent periodicities (in particular quasi‐2, ‐4, and ‐10–15 year oscillations) in the moisture time series. Copyright © 2005 Royal Meteorological Society