On the dynamics of soil moisture, vegetation, and erosion: Implications of climate variability and change

[ 1] We couple a shear-stress-dependent fluvial erosion and sediment transport rule with stochastic models of ecohydrological soil moisture and vegetation dynamics. Rainfall is simulated by the Poisson rectangular pulses rainfall model with three parameters: mean rainfall intensity, duration, and interstorm period. These parameters are related to mean annual precipitation on the basis of published data. The model is used to investigate the sensitivity of grass cover and erosion potential to drought length, changes in storm frequency under fixed mean seasonal rainfall, and variations in mean annual precipitation. Three fundamental factors, amount of precipitation, storm frequency, and soil type, are predicted to control the system response. Variation in storm frequency is predicted to have a significant influence on sediment transport capacity because of its influence on vegetation dynamics. Our results predict soil loss potential to be more sensitive to a reduction in storm frequency ( under fixed mean annual precipitation) in humid ecosystems than in arid and semiarid regions. The well-known dependence between mean annual sediment yields and precipitation ( e. g., Langbein and Schumm, 1958) is reproduced by the model. Numerical experiments using different soil types underscore the importance of soil texture in controlling the magnitude and shape of such dependence. Coupling abiotic and biotic Earth surface processes under random climatic forcing is the salient aspect of our approach, opening new avenues for research in the emerging field of complex climate-soil-vegetation-landscape dynamics.