RAINSTORM STATISTICS CONDITIONAL ON SOIL-MOISTURE INDEX - TEMPORAL AND SPATIAL CHARACTERISTICS

Soil moisture is the primary hydrological state variable that controls and it is controlled by land surface processes. Assessment of feedbac k mechanisms between land surface and the atmosphere must involve soil moisture. The Midwestern region of the United States is used as a cas e example in the preliminary investigations on the hypothesis that the structure and development of storm events are influenced by soil mois ture conditions. In particular we deal with the antecedent soil moistu re condition influence on storm precipitation amounts and interstorm d urations. The analysis based on observations indicates that when the s oil moisture is low, the ensuing interstorm duration and drying period is anomalously long. We also show that storm precipitation amounts ar e larger when the antecedent soil moisture is anomalously high. This f inding supports the hypotheses that the Summer 1993 floods over Midwes tern United States were partially forced by moist antecedent condition s.