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Abstract: Climate, lithology, soil and especially, intense land use/cover changes, make SE Spain very vulnerable to runoff generation and water erosion leading to loss of nutrients and organic matter and to infrequent but devastating floods, reservoir siltation and mass failures. This susceptibility has led to heavy economic investment and research efforts since the 1980s, making this region a worldwide reference for understanding the hydrology and geomorphology of semiarid ecosystems. Runoff and soil erosion have been intensively studied throughout the last decades in various natural ecosystems as well as in abandoned farmlands. Research has considered a wide range of methods and spatial and temporal scales. This paper reviews the methods and data describing runoff generation and water erosion, synthesising the key processes involved, rates, thresholds and controlling factors from a scale-dependent perspective. It also identifies the major gaps in current knowledge to provide recommendations for further research towards solutions that reduce the negative impacts of erosion. Research in SE Spain has contributed significantly to a better understanding of the effect of spatial and temporal scale on runoff and sediment yield measurements, and highlighted the important role of distinct erosion and sediment transport processes, hydrologic connectivity, spatial and temporal patterns of rainfall, the occurrence of extreme events and the impacts of land use changes. The most effective ways and challenges to predict runoff, soil erosion and sediment yield at the catchment scale are also discussed. [Copyright &y& Elsevier]

It is likely that climate change will increase irrigation water demand and, consequently, reduces water security in the Mediterranean Basin if current irrigation supply and demand conditions are maintained. Climate change adaptation can be achieved by (1) decreasing irrigation water demand through more efficient irrigation techniques, (2) increasing irrigation water supply by adopting new technological advances, (3) converting to rainfed agriculture, and (4) implementation of Nature-based Solutions for water retention. The aim of this study was to assess the effectiveness of different combinations of these adaptation options on water security through analysis of contrasting scenarios of socio-economic development. We defined plausible scenarios of climate change, land use change and adaptation measures for an intensively irrigated catchment in south-eastern Spain under three Shared Socioeconomic Pathways (SSP), representing different storylines of socio-economic development. We considered three SSP scenarios, including the Sustainability pathway (SSP1), the Middle of the Road pathway (SSP2) and the Fossil-fueled Development pathway (SSP5). Future land use distributions were obtained with the iClue land use change model by accounting for differences in irrigation water demand and supply, resulting in a decrease (SSP1), a constant (SSP2) and an increase (SSP5) in irrigated agriculture. The impact of each scenario on a series of water security indicators was quantified using the SPHY-MMF hydrology-soil erosion model. The SSP2 scenario, which considers very limited climate change adaptation, projects the most severe impacts on water security, including an increase in plant water stress, flood discharge, hillslope erosion and sediment yield. Under SSP1, which accounts for most climate change adaptation strategies, irrigation water demand is significantly reduced due to a shift from irrigated to rainfed agriculture and the implementation of reduced deficit irrigation, while Nature-based Solutions reduce the impact on other water security indicators. Under SSP5, a conversion from rainfed to irrigated agriculture causes a significant increase in irrigation water demand, which is met by increasing irrigation water supply from desalination. SSP5 shows intermediate impacts on other water security indicators, which is explained by a strong decrease in annual precipitation. This study helps exploring how different future socio-economic pathways affect water security and thereby supports evidence-based policy development. [Display omitted] • We considered contrasting Shared Socioeconomic Pathways in a Mediterranean catchment. • Future irrigation water supply and demand define the socio-economic scenarios. • The impact on water security was assessed using the SPHY hydrology-soil erosion model. • Climate change adaptation alleviates the impact on water security. • Policymakers should consider the benefits and trade-offs of each socio-economic path. [ABSTRACT FROM AUTHOR]

To get a full understanding of the impacts of global change on the catchment-scale sediment balance, models are needed that combine hillslope soil erosion processes with channel morphodynamics. Here we present a modification to the SPHY-MMF model that includes a novel channel morphodynamics module, which determines erosion and deposition in rills and channels. We applied the model to a Mediterranean study area in southeast Spain, in which we show that channel erosion contributes substantially (35%–40%) to the total sediment yield, highlighting the importance of accounting for channel erosion in catchment-scale sediment budget estimations. The climate change scenarios show that the different erosional processes (i.e. sheet, rill, channel) are projected to decrease or increase, depending on the projected change in annual and extreme precipitation. From this we conclude that interactions between different erosional and depositional processes should be considered when studying the impact of global change on the catchment-scale sediment balance. [Display omitted] • We present a novel channel morphodynamics module for the SPHY-MMF model. • The new module determines erosion and deposition in rills and channels. • We assessed the impacts of land use and climate change on the sediment balance. • Channel erosion contributes substantially (35%–40%) to the catchment sediment yield. • Differences in future annual and extreme precipitation control the sediment balance. [ABSTRACT FROM AUTHOR]

Agroecological practices have been shown to control erosion, increase soil fertility, carbon stocks, pollination and biodiversity. As a consequence, these ecosystem services can contribute to a better farm economic resilience on the long-term; however, empirical evidence is scarce. In this study we aim to understand the economic performance of agroecological practices in almond orchards and the relevance of different economic and policy scenarios to incentivise the upscaling of agroecological practices. We investigated the development of the net present value (NPV) of several agroecological practices (no tillage (NT), green manure (GM) and compost (CM)) as compared to conventional tillage (CT), as well as the effect of internalising externalities through payments for soil carbon sequestration and by costs of erosion. Finally, we explored the effects of price premiums and public greening payments, on farm NPV. We found that all management regimes were profitable and that CM had a 17.2% higher NPV than CT, while both GM and NT had lower NPV than CT (69% for GM and 90.1% for NT). We found that despite NT and GM have higher soil organic carbon stocks, these provided a negligible additional income via carbon markets. CT had the highest externality costs of erosion but still its NPV was higher than NT and GM, despite the strong reductions in costs of erosion in NT and GM conferred by vegetation covers. We found that a price premium of 45% was necessary to make NT's economic performance comparable to that of CT, while a 27% price premium would be needed to make GM comparable to CT. Compensation through public greening payments would be in the order of €644 ha−1 y−1 for NT and €387 ha−1 y−1 for GM to have a similar NPV as CT. Our results suggest a trade-off between income from yield and costs from unaccounted externalities. We also find that private and public policy incentives could reverse this outcome, but requiring a large investment. Of the analysed agroecological practices, compost application appears the most promising to be scaled-up to improve both economic and environmental performance, and further research is needed to determine the outcomes of a combination of compost and vegetation covers. • Agroecological practices in rainfed almonds can be profitable • Compost application resulted in higher profitability than conventional tillage • No tillage and green manure had lower profitability than conventional tillage • Public greening payments and price premiums do not fully compensate for opportunity costs • Payments for soil-based environmental services do not compensate for opportunity costs [ABSTRACT FROM AUTHOR]