Spatial patterns of drought in the interior plains of North America

A long‐period data set (1975–1978) of monthly growing season (April‐September) rainfall totals for over 400 stations in the Interior Plains of North America is used to derive a Bhalme‐and‐Mooley‐type drought index. A map‐pattern correlation technique is used to stratify the time period into distinct drought severity patterns, and maps of the mean drought patterns for each year are generated by SYMAP and examined for consistency. Based on the analyses, there are four patterns of moisture anomaly with distinct differences between the eastern, western, southern and extreme northern parts of the study region. In general, large‐scale droughts do not frequently cover the region as a whole. Indeed it seems to be the exception rather than the rule, with distinct spatial differences dominating the wet and dry years. The length and severity of drought varies from subarea to subarea, and although discrete areas do catch the brunt of drought on a year‐by‐year basis, drought occurrence in the region is largely spatially incoherent. It can therefore be concluded that drougth in the Interior Plains of North America is predominantly a non‐continental phenomenon.