The month of October is, for most of the country, the start of a new water year. The term water year is used by climatologists and hydrologists to track the use of water resources over its cycle of utilization. October is used as the beginning of the water year because across much of the United States this is the time of year when water inputs begin to exceed loss to evaporation.
During the cooler months, evaporation rates are very low, storms tend to be widespread and snow moisture will be reserved for later use. These factors allow for soil moisture to be recharged after the depletion during the warm season. In summer, evaporation and plant use usually exceeds the amount of moisture received because of the warmer temps and the more spotty nature of precipitation.
Although our wet cycle has on several occasions allowed for summer precipitation to exceed evaporation, historically, late fall and winter precipitation was an important recharge time for area soils.