Hydrologic Dynamics During the Dry Season In a Steep Forested Catchment

We have made coordinated continuous high-frequency observations of the near surface microclimate and soil moisture in a steep forested watershed in Northern California (Angelo Coast Range Reserve) for nearly a year, from a relative mild wet season into a dry summer. The observations reveal several surprises. Soil moisture by the stream decreased more rapidly than that upslope at the start of the dry season, and reached a value that was slightly higher than that upslope as the dry season progressed, even though the ABL was cooler and moister by the stream. The systematics of the spatial and temporal variations in soil moisture cannot be explained by variations in evaporation associated with ABL temperature and relative humidity. This paper presents an estimate of evaporation derived from soil moisture extraction from the catchment and a hypothesis of the processes that maintain soil moisture upslope.