For the January to December calendar year (CY) or the October to September Hydrologic Year (HY), rainfall has been nearly level over the past 55 years.

Note, the Hydrologic Year is often used when examining rainfall, flow in rivers or elevation of groundwater tables. For the Southeast, the hydrologic year begins at the normal end of the low rainfall period, which is also the time when trees and plants begin to decrease water use. Thereafter, water tends to accumulate in soil, groundwater tables rise, and river flow increases, as net rainfall exceeds net evaporation. In the latter half of the hydrologic year the opposite occurs.