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- Title
Dynamic Hillslope Soil Moisture in a Mediterranean Montane Watershed.
- Authors
Dymond, Salli F.; Wagenbrenner, Joseph W.; Keppeler, Elizabeth T.; Bladon, Kevin D.
- 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. Plain Language Summary: In Mediterranean climates, the amount of water stored in a soil is extremely important for plant transpiration and growth during the dry season and for streamflow generation during the wet season. During wet periods, the patterns of wet and dry soil across a hillslope generally correlate to topography and precipitation magnitude and frequency, with soils nearest the stream staying wetter and soils furthest from the stream staying drier. In contrast, during dry periods, soil wetness across the landscape is generally variable and largely determined by how much water the plants are using in a particular location. This study looked at the patterns of soil moisture across a hillslope over wet and dry periods to explore the dominant controls on soil moisture. We found that sites nearest the stream generally stayed wet during the wet and dry seasons, but that ridgetops located far from the stream channel were consistently wetter than mid‐slope positions during the rainy season. We also found little difference in soil moisture within the rooting zone among topographic positions. The transition from wet to dry conditions was highly variable among hillslope positions and depths and this likely reflected unmeasured factors such as small differences in local topography and vegetation. Key Points: Seasonal soil moisture largely manifested into relative wet and dry statesCounter to our expectations, ridgetops remained one of the wettest topographic positions on the landscape during the wet seasonThere was greater homogeneity in dry season soil moisture along the hillslopes
- Subjects
PLANT-water relationships; SOIL moisture; MEDITERRANEAN climate; PLANT transpiration; RIVER channels; SOIL dynamics
- Publication
Water Resources Research, 2021, Vol 57, Issue 11, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2020WR029170