The Multi-Sectoral Water Circularity Assessment (MSWCA) is a methodological framework developed for circularity assessment of the Water-Energy-Food-Ecosystems nexus. It involves five methodological steps and includes an indicators list for the selection of case-specific indicators. This study expands the MSWCA to provide a systematic approach for selecting indicators, considering system's circular actions and multi-functionality, the capture of implemented changes, the three CE principles and the sustainable development goals. Furthermore, this study differentiates between benchmark and dynamic circularity assessment and applies the expanded MSWCA in a water system of the HYDROUSA H2020 project. The benchmark assessment indicates that the HYDROUSA system achieves a 75% increase of water circularity, 76-80% increase of nutrients circularity and 14% reduction of operational `carbon footprint compared to the baseline scenario. The dynamic assessment highlights that additional measures can improve the system's circularity performance (e.g. water circularity can reach 94%) and mitigate risks occurring from uncontrollable changes.

Desertification in Mediterranean drylands threatens food security. This study evaluated biochar–compost amendments on drought-affected sandy–calcareous soils, focusing on carbon (C) and nitrogen (N) dynamics. Laboratory soil incubations revealed that biochar reduced C mineralization, aiding long-term storage, but also decreased N mineralization, signaling potential short-term immobilization. However, leaching experiments showed that incorporating 2%, 5%, 10%, and 20% biochar into compost significantly reduced C losses by 22, 26, 36, and 48%, respectively, and N losses by 37, 67%, 45%, and 65%, respectively. In water-stressed lettuce trials, the use of compost alone could only yield 30% of the yield obtained in unstressed lettuce treated with compost. While the addition of 2–5% biochar to compost enabled the conservation of 44–45% of the yield of unstressed lettuce, a 10% biochar amendment doubled this number (88%). Nonetheless, a higher dose of 20% biochar in the compost offered no additional benefit with 84% of the yield of unstressed lettuce amended with compost. These findings position biochar–compost as a key strategy to enhance soil fertility and water-use efficiency. To counteract short-term N immobilization, the study recommends further investigation of early application combined with supplemental fertilization or fractionated biochar supply (over 2–3 years). Ultimately, tailoring biochar formulations to specific local conditions is essential to balance immediate crop productivity with long-term soil health.