Intra and inter-annual variability of runoff and sediment yield of an olive micro-catchment with soil protection by natural ground cover in Southern Spain

• Hydrological-erosive patterns are explored in an olive grove catchment with a grass cover.
• Despite the cover, high soil losses are expected from events of a larger 5-year-return period.
• Although few events mostly determined annual balances, different patterns were described.
• The dense cover and the low soil moisture determined low sediment discharges in spring.

Despite the fact that the microcatchment scale allows us to evaluate the real complexity of soil protection in fields, few studies have been carried out in olive groves. This paper explores, on annual and event scales, the hydrological and erosive patterns observed in an olive microcatchment of about 6 ha under non-tillage with spontaneous grass cover, where data series of runoff and sediment load have been measured in a contrasting hydrological period of over 5 years. Firstly, the features of the data series acquired in the study station and its temporal context were explored through statistical analysis (statistics, histograms and correlation test), the intensity–duration–frequency relationships and the annual values of MOPREDAS dataset (1946–2005). In addition, annual and seasonal patterns were checked through Principal Components Analysis (PCA) to characterize the impact of rainfall variability and management techniques. Events with return periods of under 3 years caused sediment loads between 7.2 and 17.0 Mg., which implies that very high soil losses can be expected from frequent events. Although the contribution of a few events to the annual runoff and sediment load is substantial, a different distribution characterized by prolonged rainfall periods and very high soil losses was observed for a “rainy year” 2009–2010 (with an accumulated frequency of annual rainfall close to 79%). The PCA illustrated a seasonal pattern of events where low values of soil losses and sediment concentration were observed in spring. This is probably associated to lower soil moisture and to sediment being trapped by the grass cover. Finally, the minimal cost of the spontaneous cover for soil protection encourages its use, despite the fact that could be inefficient when inter-rill erosion is either not the main source of sediment in the catchment or it is not well-established.