Nonlinear Dynamics of Soil Moisture at Climate Scales: 1. Stochastic Analysis

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Abstract
Hydrologic and climatic time series are often characterized by smaller fluctuations around persistent anomalies. Occasional transitions occur between these prolonged runs of above or below average conditions. A statistical‐dynamical model is developed to represent the surface hydrology of large continental regions. The model has physically based components, and it includes a parameterization for the local recycling of precipitation. It is shown that stochastic fluctuations in this equation may give rise to separate and distinct statistical modes with noise‐induced transitions between these modes. In an example situation the characteristic long‐term probability distribution of soil moisture states is shown to be bimodal. The implications of this result are important for the interpreting and the statistical modeling of hydrologic records.