Why does soil moisture matter?

Soil moisture is one of the key factors in determining volume of spring runoff, forming a link between the previous fall’s weather and the coming season’s streamflow. Once soil freezes in winter, the water in the soil is locked in place until soils thaw in the spring, which typically coincides with the final days of snowmelt. When snowmelt does arrive, dry soils are able to absorb and hold more water than wet soils, meaning that a smaller percentage of snowmelt may become runoff following a wet fall season than a dry one. The graphs below offer a comparison between 2020 soil moisture values and average soil moisture values for soil at an 8in depth across all iRON sites.

About the graphs:

• The x-axis for all graphs represents a water year, so dates run from October of one year through September of the following year.
• Soil moisture values are for a depth of 8in. Soil moisture at an 8in depth captures changes in soil moisture across seasons, drying events, and moderate or heavy rain events. Some light rain events may not penetrate to this soil depth.
• The period of record varies for each site; exact period of record for each station is included in the graph legend. Averages from shorter periods of record may be less likely to represent overall climate/common conditions of the site than longer periods of record.
• Field capacity (wet) and wilting point (dry) are standard values set by soil type based on the force required to draw water out of the soil. They may not be representative of the soil characteristics beyond texture (e.g., root density, rockiness) or of capacity of individual plant species to extract water from the soil.

Further data can be found at: irondataboard.org.