Hydrological calibration in data-scarce catchments is challenged by non-stationary regimes, fragmented data, and systematic measurement errors. Conventional calibration approaches often assume continuous records and rely on standard performance metrics, which can bias calibration toward high flows and exacerbate parameter equifinality—ultimately reducing robustness under data limitations. This study provides a systematic comparison of three calibration strategies—Kling–Gupta Efficiency (KGE), a non-parametric variant (R_NP), and Flow Duration Curve (FDC)-based calibration—together with their time-consistent counterparts (SKGE, SR_NP, and SRMSE). All schemes are implemented for the lumped HBV-type TUW model across nine catchments in southern Italy and evaluated using independent metrics targeting overall hydrograph agreement, high-flow behavior, and FDC quantile matching (Q5–Q95). The results reveal that the time-consistent KGE-based strategy excels during in calibration (NSE = 0.56, RMSE = 4.65 m³/s) but shows notable declines in validation (NSE = 0.40, RMSE = 3.91 m³/s), indicating sensitivity to non-stationarity. The R_NP-based approach demonstrates enhanced validation robustness (NSE = 0.51, RMSE = 3.60 m³/s) and low-flow accuracy, with NSE_lnQ = 0.30 and low-flow accuracy, leveraging its non-parametric structure. The SR_NP variant further enhances performance in validation (NSE = 0.52, RMSE = 3.42 m³/s), along with superior low-flow performance (NSE_lnQ = 0.48). The FDC-based strategy effectively reproduces flow distributions during calibration (NSE = 0.41, minimal PBIAS = −0.03%) but exhibits limited temporal transferability (validation NSE = 0.25, RMSE = 4.50 m³/s). Time-consistent variants reduce parameter dispersion by approximately 2–8% (relative to full-period calibration) and improve validation metrics by 5–15% across all catchments. Overall, time-consistent calibration provides a practical pathway to increase robustness under non-stationary, data-scarce Mediterranean conditions, highlighting a systematic trade-off between calibration accuracy and validation reliability.

Nature-based solutions (NbS) have been increasingly recognized as beneficial tools for addressing various environmental and societal challenges. However, despite their growing importance, NbS are primarily funded through public finance, with significant funding gaps hindering their widespread implementation. This gap is projected to widen due to increasing multisectoral interaction of environmental systems. NbS face several barriers that prevent their scalability, including limited financing, technical challenges, and a lack of integrated, multi-disciplinary approaches. Existing research on NbS predominantly employs a single-disciplinary framework, limiting the development of comprehensive, multisectoral, and multi-scale business models that integrate private sector participation, as public funding alone is insufficient.This study proposes a novel methodology to bridge this gap by outlining a five-step process for the implementation of NbS, including: i) Local context analysis, ii) NbS Co-design, iii) NbS Impacts, iv) Business models, and v) Monitoring and evaluation. The methodology employs a circular process, designed for iterative application, ensuring that local contexts and identified societal challenges remain addressed throughout each cycle of implementation. This approach aims to develop a robust, integrative framework for NbS, ensuring that all stakeholders and local players, particularly the private sector, are engaged and that the true value of ecosystem services is internalized.By quantifying and valuating the impacts of NbS on landscapes and stakeholders, this methodology enables a better understanding of the full value of natural spaces. It promotes a shift in stakeholder perception, viewing nature not just as a public good but also as a valuable investment for the private sector. The financial participation of stakeholders helps internalize the externalities associated with natural ecosystems, such as water quality degradation and carbon sequestration. The implementation of this methodology can significantly bridge the research gap in NbS finance, leading to improved financial mechanisms, new opportunities for private finance, increased private sector involvement, and ultimately, a more sustainable and scalable approach for long-term implementation. The methodology will be presented and discussed.Acknowledgment: This work was supported by the OurMED PRIMA Program project funded by the European Union’s Horizon 2020 research and innovation under grant agreement No. 2222.