Preferential states of seasonal soil moisture: The impact of climate fluctuations

The impact of climate fluctuations on the dynamics of soil moisture is stud ied through a stochastic model of soil water balance. The analysis focuses on the changes of soil water content induced by the interannual variability of rainfall observed at the decade-to-century timescale. Extensive data an alyses have been performed to characterize the statistical properties of su ch a variability. Particular attention is paid to the year-to-year variabil ity of the average value of soil moisture during the growing season because of its relevance to the mechanisms affecting the physiology of plants and the dynamics of ecosystems. It is found that the probability distribution o f the average seasonal soil moisture may be either unimodal or bimodal depe nding on the different combinations of climate, soil, and vegetation parame ters. The possible occurrence of a double mode has both hydrologic and ecol ogic implications that are analyzed here.