Rainfall interception loss by pebble mulch in the semiarid region of China

Pebble mulches have been used to conserve soil moisture in the semiarid regions of China for over 300 years. However, little work has been carried out on rainfall interception loss by a pebble mulch layer. A field study was conducted to measure interception loss by pebble mulches during individual rainfall events, determine the rainfall-storage capacity of pebble mulch, and discuss the relationships between interception and rainfall parameters. The study showed that pebble size could affect interception loss. A 5 cm-thick pebble mulch layer, with pebbles 7.5–14.0 cm in the long dimension and 5.0–9.0 cm in the short dimension (larger pebble), had a saturation value of 0.281 mm, an average interception of 0.481 mm, and an average percentage interception of 11.5% during individual rainfall events. In contrast, a similar layer, with pebbles 2.0–6.5 cm in the long dimension and 2.0–6.0 cm in the short dimension (smaller pebble), had a saturation value of 0.526 mm, and an average interception of 0.742 mm, or 17.4% gross rainfall per storm. The correlation between interception by pebble mulch and gross rainfall was poor. The proportion of gross rainfall intercepted by pebble mulch tended to decrease as gross rainfall increased. The reduction in percentage was very marked for rains over 10 mm. Interception showed a tendency to decline with increasing rain intensity (I30). There was a broad variability in interception for intensities under 6 mm h−1. Interception tended to remain constant at about 0.25 mm for larger pebble and 0.40 mm for smaller pebble when intensity was over 6 mm h−1. Antecedent water content of pebble before a storm significantly affected interception loss, with about 50% interception occurring in the initial stage of a rainfall event. Rainfall duration and wind factors should, therefore, also be considered in future interception analysis.