The role of vegetation covers on soil wetting processes at rainfall event scale in scattered tree woodland of Mediterranean climate

- We study the role of vegetation on soil hydrological response at high time resolution.
- The soil hydrological response decreased as initial states became drier.
- The soil hydrological response was different between vegetation covers.
- The re-wetting cycles seem to be more important than precipitation amount.
- We observed rainfall threshold between covers to trigger soil hydrological response.

SummarySoil water is recognized as the key factor that controls the organization and functioning of dryland ecosystems. However, in spite of its great importance in ecohydrological processes as well as in modelling applications, most of the studies focus on daily or longer timescales, while its dynamics at shorter timescales are very little known. The main objective of this work was to determine the role of vegetation covers (grassland and tree canopy) in the soil hydrological response using measurements with high temporal resolution in evergreen oak woodland with Mediterranean climate. For this, soil water content was measured with capacitive sensors installed in the soil profile at different depths registering continuously with a high time resolution. Three study areas were monitored for two and half hydrological years. Results obtained revealed that rainwater amounts reaching the soil may temporarily be modified by covers according to precipitation properties and antecedent conditions (from dry to wet) before the rain episode. Rainfall amounts triggering a positive soil hydrological response decreased as initial states became drier, being more accentuated below tree canopies. The frequency of re-wetting cycles and the antecedent states seem to be as important or even more than either the duration or the precipitation amount. Therefore, the role of vegetation was more decisive under drier environmental conditions, where events lower than 6 mm and 2 mm never caused soil hydrological response either below tree canopy or grassland, respectively. This is important because initial conditions were independent of seasonality and because more than half of all rainfall events registered amounts smaller than 5 mm. If changes on precipitation patterns turn out in drier conditions, the predominance of such situations could have important ecohydrological consequences in semiarid ecosystems.