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Wageningen Universiteit Pays Bas (2007)

Soil moisture dynamics and land surface-atmosphere interaction

Teuling, A.J

Titre : Soil moisture dynamics and land surface-atmosphere interaction

Auteur : Teuling, A.J.

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 2007

This thesis deals with aspects of the spatial and temporal variability of soil moisture in relation to atmospheric conditions. It is first illustrated that the combination of seasonality in atmospheric forcing and non-linearity in the relation between soil moisture and the losses from the soil moisture reservoir result in a bimodal temporal distribution. Next, the impact of root water uptake on the coupled dynamics of soil moisture and evapotranspiration is investigated by a dimensionless analytical model. Subsequently, observations of evapotranspiration are used to study characteristic soil moisture response times under water-limited conditions for different biomes. Typically, these values are in the order of 15–25 days. In order to investigate the accuracy with which areal soil moisture can be estimated from a limited number of point-scale observations, rank stability analysis is applied to different field- or catchment-scale soil moisture datasets. It is shown that temporal changes in the spatial soil moisture distribution prevent perfect rank stability. Covariance analysis of Monte-Carlo simulations reveals that these changes in spatial soil moisture variability are caused by spatially variable root water uptake during drydrown, and drainage during (re)wetting. These simulations also reveal that the nonlinear relation between soil moisture and evapotranpiration in combination with climate variability induces hysteresis (i.e., non-uniqueness) in the relation between mean soil moisture and its variability. A linear analytical model is used to characterize space-time variability of surface soil moisture fields in response to minor rainfall events. The results are in good agreement with observations made during a recent field experiment conducted under very dry conditions.

Mots clés : soil water / moisture / atmosphere / soil air / plant water relations / mathematical models / temporal variation

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