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4.8.2: Soil Moisture Seasons

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    The Four Soil Moisture Seasons 

    Four soil moisture seasons can be defined by the soil moisture conditions. 

    Soil moisture seasons for Rockford, Illinois, including recharge, surplus, utilization, and deficit.
    Figure \(\PageIndex{1}\): Soil Moisture Seasons for Rockford, Illinois (CC BY-SA 4.0 ; Courtesy Michael E Ritter via The Physical Environment) 

    Figure \(\PageIndex{1}\) illustrates the seasonal soil-water budget for Rockford, Illinois, by comparing monthly precipitation (P) with potential evapotranspiration (PE). The graph identifies four distinct phases of the annual water cycle based on the balance between water supply and water demand. During the surplus season, precipitation exceeds potential evapotranspiration while the soil is already at field capacity, resulting in excess water that may contribute to runoff and groundwater recharge. As temperatures rise in late spring and summer, the utilization season begins, during which plants rely on stored soil moisture because potential evapotranspiration exceeds precipitation. When the stored soil moisture has been depleted, a deficit season develops, indicating that water demand exceeds the available supply and that additional irrigation may be necessary to support crops. In autumn and early winter, decreasing evapotranspiration and increasing moisture availability produce the recharge season, during which precipitation replenishes soil moisture and refills pore spaces until field capacity is reached once again.

    Recharge

    The recharge season is a time when water is added to soil moisture storage (+ΔST). The recharge period occurs when precipitation exceeds potential evapotranspiration but the soil has yet to reach its field capacity.

    Surplus

    The surplus season occurs when precipitation exceeds potential evapotranspiration and the soil has reached its field capacity. Any additional water applied to the soil runs off. If this water runs off into nearby streams and rivers it could cause flooding. Thus, the intensity (amount) and duration (length of season) of surplus can be used to predict the severity of potential flooding.

    Utilization

    The utilization season is a time when water is withdrawn from soil moisture storage (-ΔST). The utilization period occurs when potential evapotranspiration exceeds precipitation but soil storage has yet to reach 0 (dry soil).

    Deficit

    The deficit season occurs when occurs when potential evapotranspiration exceeds precipitation and soil storage has reached 0. This is a time when there is essentially no water for plants. Farmers then tap ground water reserves or water in nearby streams and lakes to irrigate their crops. Thus, the intensity (amount) and duration (length of season) of deficit can be used to predict the need for irrigation water.

    Whether a place experiences all four seasons depends on the climate and soil properties. Wet climate and those places with soils having high field capacities are less likely to experience a deficit period. Likewise the duration and intensity of any season will be determined by the climate and soil properties. Given equal amounts of precipitation, coarse textured soils will generate runoff faster than fine textured soils and may experience more intense surplus

    This page titled 4.8.2: Soil Moisture Seasons was last modified on Fri, 31 Jul 2026 20:24:35 GMT and is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Michael E. Ritter (The Physical Environment) via source content that was edited to the style and standards of the LibreTexts platform.