Climatic control of sediment yield in dry lands following climate and land cover change

Abstract

Long‐term climate and short‐term environmental change both affect catchment sediment yield, yet isolating the respective contributions has been difficult. To help separate the different roles, a numerical ecogeomorphic model has been used to explore the erosional impacts of different environmental changes across a gradient of annual rainfall in water‐limited fluvial landscapes. Results demonstrate that following vegetation disturbances, sediment yield is a maximum in arid to semiarid climates, decreasing in dryer climates owing to a paucity of vegetation to disturb and in wetter climates owing to increasingly rapid postdisturbance recovery. The case of sustained changes in annual rainfall is more complicated owing to trade‐offs between changes in vegetation cover and runoff. As climates abruptly become wetter, the barren, arid landscapes produce the greatest sediment, but a secondary peak occurs in semiarid climates where a high proportional increase in runoff coincides with runoff‐limited erosion. Sediment yield drops relative to prechange conditions between these two maxima, where vegetation cover substantially increases and runoff drops. Conversely, as climates become dryer, the effects of vegetation and runoff are transposed: sediment yield peaks become troughs, and troughs become peaks. Together, these results suggest that sediment yield depends both on the nature of the disturbance and on the landscape and climatic contexts in which the disturbance acts. Prechange landscapes and climate set the stage by prescribing whether sediment yield is vegetation limited or runoff limited. Environmental changes then affect erosion by augmenting or diminishing the prevailing geomorphic limitation.