A growing-season hydroclimatology, focusing on soil moisture deficits, forthe Ohio Valley region

A hydroclimatology, or description of long-term means and interannual varia tion, that focuses on soil moisture deficits was constructed for the period of 1895-1998 for a six-state region composing the Ohio Valley. The term "d eficit'' is considered from an agricultural point of view whereby moisture- induced crop stress is a combination of insufficient precipitation and soil moisture. Of particular concern are deficits that occur during the growing season (May-September) when vegetation is most susceptible to moisture-ind uced stress. Evidence suggests that there is considerable temporal variabil ity but no long-term trend toward either wetter or drier conditions in the Ohio Valley. The pattern of growing-season deficit is characterized by mult iyear and multidecadal cycles of wet and dry periods. Decreases in precipit ation during years with anomalously large growing-season deficits, however, are associated more with the reduced frequency of precipitation events tha n with any changes in intensity. These variations in precipitation frequenc y and the conditions conducive to droughts are intimately linked with large -scale atmospheric conditions, including the low-level and upper-level flow patterns.