Repeated and random components in Oklahoma's monthly precipitation record

Precipitation across Oklahoma exhibits a high degree of spatial and temporal variability and creates numerous water resources management challenges. Risk-based decision making in agricultural and water resources management may find value in knowing the extent to which historical precipitation can provide guidance for inferring expectations of future monthly precipitation. A 123-year long monthly precipitation record from the central Oklahoma climate division was evaluated, in a proof-of-concept analysis, to establish whether a simple monthly precipitation decomposition into repeatable (expected) and random (unexpected) components could identify the odds of encountering repeatable or random monthly precipitation in the future. The metric for identifying precipitation kind was based on it falling within or outside of a predetermined range, defined by the relative difference between random and a percentage of repeatable precipitation. For climate conditions in central Oklahoma, the odds of future precipitation being repeatable were between 18% and 33%, depending on the month of the year. The corresponding odds of precipitation being random were 67–82%. Thus, management decisions that rely solely on historical precipitation records to anticipate future monthly precipitation have a low probability of success in central Oklahoma.