Dynamic Hillslope Soil Moisture in a Mediterranean Montane Watershed

Salli F. Dymond, Joseph W. Wagenbrenner, Elizabeth T. Keppeler, Kevin D. Bladon

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Variations in hillslope soil moisture control forest hydrologic fluxes and storage pools, yet sparse observations combined with the complexity and heterogeneity of water movement and storage in the vadose zone can make temporal and spatial patterns and processes difficult to predict. We used two years of field observations of volumetric soil moisture at three depths (15, 30, and 100 cm) across five topographic positions (riparian, toeslope, sideslope, shoulder, and ridge) along three hillslope transects to better understand how soil moisture changes with hillslope position and through time. As expected, we found higher values of soil moisture at all depths at the riparian and toeslope positions. Unexpectedly, we found that ridges were particularly wet during the wet winter months and dried quickly during the summer months, indicating that topography alone cannot account for mean wet season soil moisture in our Mediterranean climate field site. The variability in soil moisture across all soil depths and topographic positions was greatest when soils were dry and decreased under wet soil conditions; this variability remained high in the deeper soil horizons, regardless of season. Lastly, event analysis suggests that the response to early season rainfall was highly variable along the hillslopes and was likely dominated by localized controls such as microtopography and vegetation as well as soil texture, antecedent moisture conditions, and rainfall characteristics. Our results suggest that the drivers of wet and dry season soil moisture dynamics can vary across topographic positions along a hillslope and do not always follow topographic controls.

Original languageEnglish (US)
Article numbere2020WR029170
JournalWater Resources Research
Volume57
Issue number11
DOIs
StatePublished - Nov 2021

Bibliographical note

Funding Information:
Funding and support for this research was provided by the California Department of Forestry and Fire Protection, the USDA Forest Service Pacific Southwest Research Station (PSW), and National Science Foundation (NSF) (NSF‐EAR‐1807165). We thank Brian Storms, Megan Arnold, and the Caspar Creek Watershed Experiment field team for field and technical assistance. Special thanks to Chris Faubion (PSW) for soil sampling, Ryan Cole (ORISE‐PSW), Caroline Ristuccia, and Diane Sutherland (PSW) for processing soil samples, and Shelby Hammerschmidt (PSW) for reviewing data and making maps. Thank you to Dave Longstreth and Patrick Brand (California Geological Survey) for assistance with interpreting the underlying geologic formations at Caspar Creek.

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.

Keywords

  • forest soils
  • hillslope hydrology
  • soil drawdown
  • soil water
  • soil wetness
  • topography

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