Seasonal and spatial variations in infiltration rates in badland surfaces under Mediterranean climatic conditions

This paper investigates the spatial and temporal variations of infiltration rates on badland landscapes under Mediterranean climatic conditions of the eastern Iberian Peninsula. Soil infiltration was measured under simulated rainfall and by cylinder infiltrometer for typical winter, spring, summer, and autumn conditions. The spatial variability of infiltration within the badland landscapes is determined by the two main geomorphological units: slopes and pediments. Slopes show greater steady state infiltration rates than pediments (averaging 6.6 and 11.9 mm h(-1), respectively), but they generate faster runoff and the runoff curves are steeper than on the slopes. For short thunderstorms, pediments generate more runoff because soils on the slopes have a wider and deeper crack network, which favors higher infiltration rates at the beginning of the rainfall. However, for simulated storms of 40 min duration, the runoff rate on the slopes (74.3%) is slightly greater than on the pediments (72.5%) due to their lower steady state infiltration rate. For both slopes and pediments, greater steady state infiltration rates were measured under simulated rainfall (fc) for summer (18.9 and 11.6 mm h(-1)) than for winter (11.8 and 6.8 mm h(-1)), spring (3.8 and 8.7 mm h(-1)), and autumn (4.1 and 8.3 mm h(-1)) for slope and pediment positions, respectively. Measurements by means of cylinder infiltrometer (ifc) confirm these seasonal trends. On the pediment plots, ifc varies from 43 mm h(-1) in winter to 26 mm h(-1) in spring, rises to 62 mm h(-1) in summer, and finally drops to 26 mm h(-1) in autumn. For the slope positions, ifc has a similar seasonal trend: 18 mm h(-1) in winter, 9 mm h(-1) in spring, 52 mm h(-1) in summer, and 10 mm h(-1) in autumn. Measurements by means of cylinder infiltrometer results in 3 times greater steady state infiltration rates due to the effect of water depth pressure and crust development under simulated rainfall. In summer the development of wide and deep cracks results in macropore flow, and these are important factors in pipe initiation.