Temporal variability and time compression of sediment yield in small Mediterranean catchments: impacts for land and water management

Abstract

Increased soil erosion, pressure on agricultural land, and climate change highlight the need for new management methods to mitigate soil loss. Management strategies should utilize comparable data sets of long‐term soil erosion monitoring across multiple environments. Adaptive soil erosion management in regions with intense precipitation requires an understanding of inter‐annual variability in sediment yield (SY) at regional scales. Here, a novel approach is proposed for analysing regional SY. We aimed to (i) investigate factors controlling inter‐ and intra‐annual SY, (ii) combine seasonality and time compression analyses to explore SY variability and (iii) discuss management implications for different Mediterranean environments. Continuous SY measurements totalling 104 years for eight small catchments were used to describe SY variability, which ranged from 0 to 271 t/ha/year and 0 to 116 t/ha/month. Maximum SY occurs in spring to summer for catchments with oceanic climates, while semi‐arid or dry summer climates experience SY minimums. We identified three time compression patterns at each time scale. Time compression was most intense for catchments with minimum SY in spring to summer. Low time compression was linked to very high soil loss, low run‐off and sediment production thresholds, and high connectivity. Reforestation, grassland and terracing changed SY magnitudes and time compression, but failed to reduce SY for large storm events. Periods with a high probability of high SY were identified using a combination of intra‐annual SY variability, seasonality analysis, and time compression analysis. Focusing management practices on monthly flow events, which account for the majority of SY, will optimise returns in Mediterranean catchments.

Relationship of Weather Types on the Seasonal and Spatial Variability of Rainfall, Runoff, and Sediment Yield in the Western Mediterranean Basin

“…Our results are in line with previous studies showing that seasonal patterns of rainfall and runoff are highly variable depending on the study sites [77][78][79]. For example, Smetanova et al [80] performed an analysis of the seasonal distribution of the sediment for different environments in the Mediterranean. The highest SY response occurs in spring and summer for catchments with oceanic climates, while catchments with semi-arid or dry climates experience minimum values in summer.…”

Mesoscale Mapping of Sediment Source Hotspots for Dam Sediment Management in Data-Sparse Semi-Arid Catchments

“…Hereby, sediment production and transport through landscape rather than runoff generation and propagation through landscape are in the focus, without considering the sediment production and transport in permanent streams. The occurrence of high intensity interval rainfall events, which are linked closely to peaks in sediment delivery [34,35]. Density and diversity of above-ground and sub-surface (roots) biomass influence infiltration, while vegetation patterns impact infiltration and connectivity of water and sediments in the landscapes [36][37][38][39][40].…”

“…To our knowledge, this is rarely the case in sediment management. For example, studies showed that amount of sediment leaving a catchment at its outlet (furthermore, sediment yield) is closely related to rainfall seasonality and rainfall extremes in semi-arid catchments (e.g., [35,86]). However, the relation between rainfall amount and sediment yield is not linear, while redistribution of sediment in catchment or in river channel influence sediment yield when the catchment is well connected during the event.…”

“…Despite good understanding of functioning of bio-physical systems in semi-arid areas [37,38,116,117], local eco-hydrological and eco-geomorphological conditions can stimulate specific catchment sediment responses [118,119]. Regional studies showed that rainfall-discharge-sediment response curves and some of the controlling factors varied among catchments and/or seasons [14,35,44,120]. Events of similar magnitude can deliver differing amounts of sediment if intra-or inter-event catchment connectivity changed, or stored sediment was released within an event [121].…”

“…), amount of fertilizer, or number of cattle breeding on semi-natural pastures, which all contribute to land and water quality degradation. Multi-factor character of many environmental problems is well acknowledged in science, but not reflected in institutional structures and institutions' cooperation networks in many countries, and transboundary basins [35,130,131]. The call for transdisciplinary research in the land degradation community has existed for a longer time, all the while acknowledging the need to address societal challenges is evermore present.…”