Exploring the dynamic nexus between SDG 7 and SDG 9: A wavelet–quantile perspective in Portugal

This study examines the dynamic and frequency-dependent nexus between Sustainable Development Goal 7 (SDG 7 – Affordable and Clean Energy) and Sustainable Development Goal 9 (SDG 9 – Industry, Innovation and Infrastructure) in Portugal. Despite the growing literature on sustainable transitions, the relationship between clean energy development and industrial innovation, although studied through quantile-based and wavelet-quantile approaches, remains underexplored at the country-specific level, particularly in Portugal from a time–frequency–quantile perspective. Using quarterly series derived from annual data and covering 2000Q1 to 2024Q4, the study employed wavelet-based econometric techniques—specifically wavelet quantile cointegration, wavelet quantile regression, and wavelet quantile correlation—to capture the linkage between the two SDGs across multiple time scales and quantiles. The results indicated that a higher SDG 7 index score was more strongly and positively associated with SDG 9 in the medium to long term, while SDG 9 was significantly associated with SDG 7 across all time periods and quantiles. Moreover, the wavelet quantile correlation showed strong long-term co-movement between the two SDGs, consistent with structural complementarity in Portugal's sustainable development pathway. These findings highlight the importance of integrating clean energy strategies with industrial innovation policies. Enhancing R&D incentives for energy-efficient technologies, promoting green infrastructure, and fostering public–private partnerships can amplify mutual gains between energy and innovation. The results emphasize that aligning energy transition policies with innovation-driven industrial frameworks may help accelerate Portugal's progress toward achieving a resilient, low-carbon, and innovation-oriented economy by 2030.